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NOD32

2007-09-27T05:56:00.000-07:00

NOD32 is an antivirus package made by the Slovak company Eset. Versions are available for Microsoft Windows, Linux, FreeBSD, and other platforms. Remote administration tools for multiuser installations are also available at extra cost. A NOD32 Enterprise Edition is available that consists of NOD32 AntiVirus and NOD32 Remote Administrator. The NOD32 Remote Administrator program allows a network administrator to monitor anti-virus functions, push installations and upgrades to unprotected PCs on the network, and update configuration files from a central location.

History

NOD32 was born in the early 1990s when computer viruses were becoming increasingly prevalent.

Initially the program gained popularity with IT workers in Eastern European countries, as Eset was based in Slovakia. Though the program's abbreviation was originally pronounced as individual letters, recent worldwide use of the program has led to the more common single-word pronunciation, sounding like the English word "nod".

Current versions of NOD32 are very different from the original NOD software. Several generations of the program have been developed as a response to a rapidly changing attack pattern by increasingly complex viruses. The program, now for both 32-bit and 64-bit systems^[, is known as NOD32, replacing the older 16-bit flagship product, NOD-ICE.

Naming

At the time of its creation, the popular television program Nemocnica na Okraji Mesta, or "Hospital at the Edge of the City" was broadcasting on many European television networks. Early viruses often targeted hard disk boot sectors, located near the edge of the disk. As a pun, the program's creators named their new anti-virus program the "Nemocnica na Okraji Disku", "Hospital at the Edge of the Disk", giving it the initials NOD.

Technical information

NOD32 consists of an on-demand scanner and four different real-time monitors. The on-demand scanner (somewhat confusingly referred to as NOD32) can be invoked by the scheduler or by the user. Each real-time monitor covers a different virus entry point:

AMON (Antivirus MONitor) - scans files as they are accessed by the system, preventing a virus from executing on the system.

DMON (Document MONitor) - scans Microsoft Office documents and files for macro viruses as they are opened and saved by Office applications.

IMON (Internet MONitor) - intercepts traffic on common protocols such as POP3 and HTTP to detect and intercept viruses before they are saved to discs.

EMON (E-mail MONitor) - An auxiliary module for scanning incoming/outgoing e-mails via the MAPI interface, such as Microsoft Outlook and Microsoft Exchange.

XMON (MS eXchange MONitor) - scans incoming and outgoing mail when NOD32 is running and licensed for Microsoft Exchange Server - ie, running on a server environment. This module is not present on workstations at all.

NOD32 AMON Virus Detection Alert

NOD32 is written largely in assembly code , which contributes to its low use of system resources and scanning speed. NOD32 can process more than 23MB per second while scanning on a P4 based PC and, on average, uses less than 20MB of memory in total. The physical RAM used is often just a third of that.

According to a 2005 Virus Bulletin test, NOD32 performs scans two to five times faster than other antivirus competitors.

In a networked environment NOD32 clients can update from a central "mirror server" on the network, reducing bandwidth usage since new definitions need only be downloaded once by the mirror server as opposed to once for each client.

In addition to signature files, NOD32's scan engine uses heuristic detection (called "ThreatSense" by Eset) to provide better protection against newly released viruses.

Future Development

Screenshot of NOD32 v3 (Beta 2)

Eset has released beta versions of a new version (version 3) of NOD32 Anti-Virus. NOD32 Version 3 will include a redesigned graphical interface, intended to be more user friendly.

Eset Smart Security

Eset is also currently in the beta stages of developing an internet security suite, called Eset Smart Security. Eset Smart Security is intended to compete with other internet security suites, such as Norton Internet Security and Kaspersky Internet Security.

Eset Smart Security is planned to include the following features:

NOD32 Anti-Virus engine (the next version of Eset's anti-malware engine (NOD32 v3.0))
Firewall (with port stealthing and advanced filtering features)
Anti-Spam (filtering with Bayesian filter, whitelisting and blacklisting)

Antivirus software

2007-09-27T05:50:00.000-07:00

Antivirus software consists of computer programs that attempt to identify, thwart and eliminate computer viruses and other malicious software (malware).

Antivirus software typically uses two different techniques to accomplish this:

Examining (scanning) files to look for known viruses matching definitions in a virus dictionary
Identifying suspicious behavior from any computer program which might indicate infection. Such analysis may include data captures, port monitoring and other methods.

Most commercial antivirus software uses both of these approaches, with an emphasis on the virus dictionary approach.

Approaches

Dictionary

In the virus dictionary approach, when the antivirus software looks at a file, it refers to a dictionary of known viruses that the authors of the antivirus software have identified. If a piece of code in the file matches any virus identified in the dictionary, then the antivirus software can take one of the following actions:

attempt to repair the file by removing the virus itself from the file
quarantine the file (such that the file remains inaccessible to other programs and its virus can no longer spread)
delete the infected file

To achieve consistent success in the medium and long term, the virus dictionary approach requires periodic (generally online) downloads of updated virus dictionary entries. As civically minded and technically inclined users identify new viruses "in the wild", they can send their infected files to the authors of antivirus software, who then include information about the new viruses in their dictionaries.

Dictionary-based antivirus software typically examines files when the computer's operating system creates, opens, closes or e-mails them. In this way it can detect a known virus immediately upon receipt. Note too that a System Administrator can typically schedule the antivirus software to examine (scan) all files on the computer's hard disk on a regular basis.

Although the dictionary approach can effectively contain virus outbreaks in the right circumstances, virus authors have tried to stay a step ahead of such software by writing "oligomorphic", "polymorphic" and more recently "metamorphic" viruses, which encrypt parts of themselves or otherwise modify themselves as a method of disguise, so as to not match the virus's signature in the dictionary.

Suspicious behavior

The suspicious behavior approach, by contrast, doesn't attempt to identify known viruses, but instead monitors the behavior of all programs. If one program tries to write data to an executable program, for example, the antivirus software can flag this suspicious behavior, alert a user and ask what to do.

Unlike the dictionary approach, the suspicious behavior approach therefore provides protection against brand-new viruses that do not yet exist in any virus dictionaries. However, it can also sound a large number of false positives, and users probably become desensitized to all the warnings. If the user clicks "Accept" on every such warning, then the antivirus software obviously gives no benefit to that user. This problem has worsened since 1997^{[citation needed]}, since many more nonmalicious program designs came to modify other .exe files without regard to this false positive issue. Thus, most modern antivirus software uses this technique less and less.

Other approaches

Some antivirus software use other types of heuristic analysis. For example, it could try to emulate the beginning of the code of each new executable that the system invokes before transferring control to that executable. If the program seems to use self-modifying code or otherwise appears as a virus (if it immediately tries to find other executables, for example), one could assume that a virus has infected the executable. However, this method could result in a lot of false positives.

Yet another detection method involves using a sandbox. A sandbox emulates the operating system and runs the executable in this simulation. After the program has terminated, software analyzes the sandbox for any changes which might indicate a virus. Because of performance issues, this type of detection normally only takes place during on-demand scans. Also this method may fail as viruses can be nondeterministic and result in different actions or no actions at all done when run - so it will be impossible to detect it from one run.

Some virus scanners can also warn a user if a file is likely to contain a virus based on the file type.

An emerging technique to deal with malware in general is whitelisting. Rather than looking for only known bad software, this technique prevents execution of all computer code except that which has been previously identified as trustworthy by the system administrator. By following this default deny approach, the limitations inherent in keeping virus signatures up to date are avoided. Additionally, computer applications that are unwanted by the system administrator are prevented from executing since they are not on the whitelist. Since modern enterprise organizations have large quantities of trusted applications, the limitations of adopting this technique rest with the system administrators' ability to properly inventory and maintain the whitelist of trusted applications. As such, viable implementations of this technique include tools for automating the inventory and whitelist maintenance processes.

Issues of concern

The ongoing writing and spreading of viruses and of panic about them gives the vendors of commercial antivirus software a financial interest in the ongoing existence of viruses. Some theorize that antivirus companies have financial ties to virus writers, to generate their own market, though there is currently no evidence for this.
Some antivirus software can considerably reduce performance. Users may disable the antivirus protection to overcome the performance loss, thus increasing the risk of infection. For maximum protection the antivirus software needs to be enabled all the time — often at the cost of slower performance (see also software bloat).
It is important to note that one should not have more than one antivirus software installed on a single computer at any given time. This can seriously cripple the computer and cause further damage.
It is sometimes necessary to temporarily disable virus protection when installing major updates such as Windows Service Packs or updating graphics card drivers.^{[citation needed]} Having antivirus protection running at the same time as installing a major update may prevent the update installing properly or at all.
When purchasing antivirus software, the agreement may include a clause that your subscription will be automatically renewed, and your credit card automatically billed at the renewal time without your approval. For example, McAfee requires one to unsubscribe at least 60 days before the expiration of the present subscription.^{[citation needed]} In that case, the subscriber may contest the charges with the credit card issuer, but this recourse is likely to fail if in fact the subscriber had authorised such a "continuous payment authority".
Some antivirus programmes are actually spyware masquerading as antivirus software. It is best to double-check that the antivirus software which is being downloaded is actually a real antivirus program.
Some commercial antivirus software programs contain adware. For example, the home/small business version of CA Anti-Virus 2008 displays an advert for CA products whenever the desktop is unlocked after a period of inactivity.

Antivirus, mobile devices and innovative solutions

It would be no surprise when viruses that plague the desktop and laptop world quickly migrate to mobile devices. More and more vendors in this space are offering solutions to combat secure mobile handsets with antivirus solutions. Mobile devices present significant challenges for antivirus software, such as:

Processor Constraints
Memory Constraints
Definitions and new signature updates to these mobile handsets

SIM, flash based and USB based antivirus products

Mobile handsets are now offered with a variety of interfaces and data connection capabilities. Consumers should carefully evaluate security products before deploying on small form factor devices.

Solutions that are hardware-based, perhaps USB devices or SIM-based antivirus solutions, might work better in meeting the needs of mobile handset consumers. Technical evaluation and review on how deploying an antivirus solution on cellular mobile handsets should be considered as scanning process might impact other legitimate applications on the handheld.

SIM-based solutions with antivirus integrated on the small memory footprint might provide a basic solution to combat malware/viruses in protecting PIM and mobile user data. USB and Flash memory-based solutions give the user an advantage to swap and use these products with a range of hardware devices.

History

There are competing claims for the innovator of the first antivirus product. Perhaps the first publicly known neutralization of a wild PC virus was performed by European Bernt Fix (also Bernd) in early 1987. Fix neutralized an infection of the Vienna virus. First edition of Polish antivirus software mks_vir started in 1987. Program was only available in Polish language version. Fall 1988 also saw antivirus software Dr. Solomon's Anti-Virus Toolkit released by Briton Alan Solomon. By December 1990 the market had matured to the point of nineteen separate antivirus products being on sale including Norton AntiVirus and ViruScan from McAfee.

Peter Tippett made a number of contributions to the budding field of virus detection.^{[citation needed]} He was an emergency room doctor who also ran a computer software company. He had read an article about the Lehigh virus and questioned whether they would have similar characteristics to biological viruses that attack organisms. From an epidemiological viewpoint, he was able to determine how these viruses were affecting systems within the computer (the boot-sector was affected by the Brain virus, the .com files were affected by the Lehigh virus, and both .com and .exe files were affected by the Jerusalem virus). Tippett’s company Certus International Corp. then began to create anti-virus software programs. The company was sold in 1992 to Symantec Corp, and Tippett went to work for them, incorporating the software he had developed into Symantec’s product, Norton AntiVirus.^{[citation needed]}

A very uncommon use of the term "antivirus" is to apply it to benign viruses that spread and combated malicious viruses. This was common on the Amiga computer platform.^{[citation needed]}

Random Access Memory

2007-09-27T05:41:00.000-07:00

Random access memory (usually known by its acronym, RAM) is a type of data storage used in computers. It takes the form of integrated circuits that allow the stored data to be accessed in any order — that is, at random and without the physical movement of the storage medium or a physical reading head. RAM is a volatile memory as the information or instructions stored in it will be lost if the power is switched off.

The word "random" refers to the fact that any piece of data can be returned in a constant time, regardless of its physical location and whether or not it is related to the previous piece of data.This contrasts with storage mechanisms such as tapes, magnetic discs and optical discs, which rely on the physical movement of the recording medium or a reading head. In these devices, the movement takes longer than the data transfer, and the retrieval time varies depending on the physical location of the next item.

Terminology

A 1GB DDR RAM memory

Originally, RAM referred to a type of solid-state memory, and the majority of this article deals with that, but physical devices which can emulate true RAM (or, at least, are used in a similar way) can have "RAM" in their names: for example, DVD-RAM.

RAM is usually writable as well as readable, so "RAM" is often used interchangeably with "read-write memory". The alternative to this is "ROM", or Read Only Memory. Most types of RAM lose their data when the computer powers down. "Flash memory" is a ROM/RAM hybrid that can be written to, but which does not require power to maintain its contents. RAM is not strictly the opposite of ROM, however. The word random indicates a contrast with serial access or sequential access memory.

"Random access" is also the name of an indexing method: hence, disk storage is often called "random access" because the reading head can move relatively quickly from one piece of data to another, and does not have to read all the data in between. However the final "M" is crucial: "RAM" (provided there is no additional term as in "DVD-RAM") always refers to a solid-state device.

Many CPU-based designs actually have a memory hierarchy consisting of registers, on-die SRAM caches, DRAM, paging systems, and virtual memory or swap space on a hard-drive. This entire pool of memory may be referred to as "RAM" by many developers, even though the various subsystems can have very different access times, violating the original concept behind the "random access" term in RAM. Even within a hierarchy level such as DRAM, the specific row/column/bank/rank/channel/interleave organization of the components make the access time variable, although not to the extent that rotating storage media or a tape is variable.

Overview

The key benefit of RAM over types of storage which require physical movement is that retrieval times are short and consistent. Short because no physical movement is necessary, and consistent because the time taken to retrieve a piece of data does not depend on its current distance from a physical head; it requires practically the same amount of time to access any piece of data stored in a RAM chip. Most other technologies have inherent delays for reading a particular bit or byte. The disadvantage of RAM over physically moving media is cost, and the loss of data when power is turned off.

Because of this speed and consistency, RAM is used as 'main memory' or primary storage: the working area used for loading, displaying and manipulating applications and data. In most personal computers, the RAM is not an integral part of the motherboard or CPU—it comes in the easily upgraded form of modules called memory sticks or RAM sticks about the size of a few sticks of chewing gum. These can quickly be removed and replaced should they become damaged or too small for current purposes. A smaller amount of random-access memory is also integrated with the CPU, but this is usually referred to as "cache" memory, rather than RAM.

Modern RAM generally stores a bit of data as either a charge in a capacitor, as in dynamic RAM, or the state of a flip-flop, as in static RAM. Some types of RAM can detect or correct random faults called memory errors in the stored data, using RAM parity and error correction codes.

Many types of RAM are volatile, which means that unlike some other forms of computer storage such as disk storage and tape storage, they lose all data when the computer is powered down. For these reasons, nearly all PCs use disks as "secondary storage". Small PDAs and music players (up to 8 GB in Jan 2007) may dispense with disks, but rely on flash memory to maintain data between sessions of use.

Software can "partition" a portion of a computer's RAM, allowing it to act as a much faster hard drive that is called a RAM disk. Unless the memory used is non-volatile, a RAM disk loses the stored data when the computer is shut down. However, volatile memory can retain its data when the computer is shut down if it has a separate power source, usually a battery.

If a computer becomes low on RAM during intensive application cycles, the computer can resort to so-called virtual memory. In this case, the computer temporarily uses hard drive space as additional memory. Constantly relying on this type of backup memory it is called thrashing, which is generally undesirable, as virtual memory lacks the advantages of RAM. In order to reduce the dependency on virtual memory, more RAM can be installed.

Recent developments

Currently, several types of non-volatile RAM are under development, which will preserve data while powered down. The technologies used include carbon nanotubes and the magnetic tunnel effect.

In summer 2003, a 128 KB magnetic RAM chip manufactured with 0.18 µm technology was introduced. The core technology of MRAM is based on the magnetic tunnel effect. In June 2004, Infineon Technologies unveiled a 16 MB prototype again based on 0.18 µm technology.

Nantero built a functioning carbon nanotube memory prototype 10 GB array in 2004.

In 2006, Solid state memory came of age, especially when implemented as "Solid state disks", with capacities exceeding 150 gigabytes and speeds far exceeding traditional disks. This development has started to blur the definition between traditional random access memory and disks, dramatically reducing the difference in performance.

Memory wall

The "memory wall" is the growing disparity of speed between CPU and memory outside the CPU chip. An important reason of this disparity is the limited communication bandwidth beyond chip boundaries. From 1986 to 2000, CPU speed improved at an annual rate of 55% while memory speed only improved at 10%. Given these trends, it was expected that memory latency would become an overwhelming bottleneck in computer performance.

Currently, CPU speed improvements have slowed significantly partly due to major physical barriers and partly because current CPU designs have already hit the memory wall in some sense. Intel summarized these causes in their Platform 2015 documentation (PDF):

“First of all, as chip geometries shrink and clock frequencies rise, the transistor leakage current increases, leading to excess power consumption and heat (more on power consumption below). Secondly, the advantages of higher clock speeds are in part negated by memory latency, since memory access times have not been able to keep pace with increasing clock frequencies. Third, for certain applications, traditional serial architectures are becoming less efficient as processors get faster (due to the so-called Von Neumann bottleneck), further undercutting any gains that frequency increases might otherwise buy. In addition, resistance-capacitance (RC) delays in signal transmission are growing as feature sizes shrink, imposing an additional bottleneck that frequency increases don't address.”

The RC delays in signal transmission were also noted in Clock Rate versus IPC: The End of the Road for Conventional Microarchitectures which projects a maximum of 12.5% average annual CPU performance improvement between 2000 and 2014. The data on Intel Processors clearly shows a slowdown in performance improvements in recent processors. However, Intel's new processors, Core 2 Duo (codenamed Conroe) show a significant improvement over previous Pentium 4 processors; due to a more efficient architecture, performance increased while clock rate actually decreased.

DRAM packaging

For economic reasons, the large (main) memories found in personal computers, workstations, and non-handheld game-consoles (such as Playstation and Xbox) normally consists of dynamic RAM (DRAM). Other parts of the computer, such as cache memories and data buffers in hard disks, normally use static RAM (SRAM).

PC motherboard

2007-09-27T05:31:00.000-07:00

A PC motherboard is a printed circuit board used in a personal computer. It is also known as the mainboard or planar board and occasionally abbreviated to mobo or MB. The term mainboard is also used for the main circuit board in this and other electronic devices.

A typical motherboard provides attachment points for one or more of the following: CPU, graphics card, sound card, hard disk controller, memory (RAM), and external peripheral devices. The connectors for external peripherals are nearly always color coded according to the PC 99 specification.

All of the basic circuitry and components required for a computer to function sit either directly on the motherboard or in an expansion slot of the motherboard or are connected with a cable. The most important component on a motherboard is the chipset. It often consists of two components or chips known as the Northbridge and Southbridge, though they may also be integrated into a single component. These chips determine, to an extent, the features and capabilities of the motherboard.

The remainder of this article discusses the state of the so-called "IBM compatible PC" motherboard in the early 2000s. It contains the chipset, which controls the operation of the CPU, the PCI, ISA, AGP, and PCI Express expansion slots, and (usually) the IDE/ATA controller as well. Most of the devices that can be attached to a motherboard are attached via one or more slots or sockets, although some modern motherboards support wireless devices using the IrDA, Bluetooth, or 802.11 (Wi-Fi) protocols.

CPU sockets

There are different slots and sockets for CPUs, and it is necessary for a motherboard to have the appropriate slot or socket for the CPU. Newer sockets, those with a three digit number, are named after the number of pins they contain. Older ones are simply named in the order of their invention, usually with a single digit.

Sockets supporting Intel processors

Socket 6 - 80486DX4
Socket 7 - Intel Pentium and Pentium MMX, AMD K6 and some Cyrix CPUs)
Socket 8 - Intel Pentium Pro
Slot 1 - Intel Pentium II, older Pentium III, and Celeron processors (233 MHz - 1.13 GHz)
Slot 2 - Intel Xeon processors based on Pentium II/III cores
Socket 370 - Celeron processors and newer Pentium IIIs (700 MHz - 1.4 GHz)
Socket 423 - Intel Pentium 4 and Celeron processors (based on the Willamette core)
Socket 478 - Intel Pentium 4 and Celeron processors (based on Northwood, Prescott, and Willamette cores)
Socket 479 - Intel Pentium M and Celeron M processors (based on the Banias and Dothan cores)
Socket M - Intel Core processors (based on the Yonah core)
Socket 603 / 604 - Intel Xeon processors based on the Northwood and Willamette Pentium 4 cores
Socket T / LGA 775 (Land Grid Array) - Intel Pentium 4, Core 2, and Celeron processors (based on Northwood, Prescott, Conroe, Kentsfield, and Cedar Mill cores)
LGA 771 (Land Grid Array) - Intel Xeon Core 2, and based on Woodcrest cores

Sockets supporting AMD CPUs

Slot A - or Socket 462 (aka Socket A) - newer AMD Athlon, Athlon XP, Sempron, and Duron processors
Socket 754 - lower end AMD Athlon 64 and Sempron processors with single-channel memory support
Socket 939 - AMD Athlon 64, AMD Athlon 64 FX, AMD Athlon 64 X2, and AMD Opteron processors with dual-channel memory support
Socket 940 - AMD Opteron and early AMD Athlon FX processors
Socket AM2 - Sempron, AMD Athlon 64, AMD Athlon 64 X2, AMD Athlon 64 FX and AMD Opteron (AMD Phenom?)
Socket F - AMD Opteron and high-end AMD Athlon 64 FX

Peripheral card slots

There are usually a number of expansion card slots to allow peripheral devices and cards to be inserted. Each slot is compatible with one or more industry bus standards. Commonly available buses include: PCI (Peripheral Component Interconnect), PCI-X, AGP (Accelerated Graphics Port), and PCI Express.

ISA was the original bus for connecting cards to a PC. Despite significant performance limitations, it was not superseded by the more advanced but incompatible MCA (Micro Channel Architecture) (IBM's proprietary solution which appeared in their PS/2 series of computers and a handful of other models) or the equally advanced and backward-compatible EISA (Extended Industry Standard Architecture) bus. It endured as a standard feature in PCs till the end of the 20th century, aided first by the brief dominance of the VESA (Video Electronic Standards Association) extension during the reign of the 486 and later by the need to accommodate the large number of existing ISA peripheral cards. The more recent PCI bus is the current industry standard, which initially was a high-speed supplement to ISA for high-bandwidth peripherals (notably graphics cards, network cards, and SCSI host adaptors), and gradually replaced ISA as a general-purpose bus. An AGP slot is a high speed, single-purpose port designed solely for connecting high performance graphics cards (which produce video output) to the monitor. Both AGP and PCI buses are marked for replacement by PCI Express, although this is unlikely to happen prior to 2006 because of the large established base of AGP/PCI motherboards and add-in cards.

A typical motherboard of 1999 might have had one AGP slot, four PCI slots, and one (or two) ISA slots; since about 2002 the last ISA slots in new boards have been replaced with extra PCI slots. Sometimes an Advanced Communications Riser slot is used instead on less expensive motherboards.

As of 2001, most PCs also support Universal Serial Bus (USB) connections, and the controller and ports required for this are usually integrated onto the motherboard. An ethernet interface and a basic audio processor are now almost universally integrated into current motherboards as well.

Temperature and reliability

Generally, motherboards are air cooled with heat sinks on the larger chips such as the northbridge and CPU, and they have monitored sockets for case fans. Newer motherboards have integrated temperature sensors to detect motherboard and CPU temperatures, which can be used by the BIOS or Operating system to regulate fan speed. The removal of waste thermal energy became a major concern for workstation PCs around 2000, with the problem becoming more severe over time as computer systems continued to consume more and more power.

A study of the German c't computer magazine c't 2003, vol. 21 pg. 216-221 found that some spurious computer crashes and general reliability issues ranging from screen image distortions to I/O read/write errors can surprisingly be attributed not to software or peripheral hardware but to aging PC motherboards.

Motherboard voltage regulation uses electrolytic capacitors. These capacitors exhibit aging effects which depend on the temperature of the parts, since their water based electrolytes slowly evaporate leading to capacity loss and motherboard malfunctions due to voltage instabilities. While most capacitors are rated for 2000 hours at 105 °C (life formula ), their expected design life roughly doubles for every 10 °C below this. At 45 °C a lifetime of 15 years can be expected, which appears reasonable for a computer mainboard. In the past, many manufacturers delivered substandard capacitors, which would reduce this life expectancy figure. With inadequate case cooling this can become a serious problem. It is, however, possible to find and replace broken capacitors on PC mainboards. For more information on certain types of premature capacitor failure on PC motherboards, see capacitor plague.

Form factor

The motherboard fits into the computer case with screws or clips. There are many form factors, or sizes of motherboard. In general, it is necessary for the case, power supply, and motherboard to conform to the same standard in order for them to operate properly.

As new generations of components have been developed, the standards for motherboard design have changed too - for example with AGP being introduced, and more recently PCI Express. However the basic standardized size and layout of motherboard have changed much more slowly, and are controlled by their own standards. This is helped by the fact that in many ways, the list of components a motherboard must include changes far slower than the components themselves. For example, north bridge controllers have changed many times since their original introduction, with many manufacturers bringing out their own versions, but in terms of form factor standards, the requirement to allow for a north bridge has remained fairly static for many years.

Differences between form factors are most apparent in terms of their intended market sector, and involve variations in size, design compromises and typical features. Most modern computers have very similar requirements, so form factor differences tend to be based upon subsets and supersets of these. For example, a desktop computer may require more sockets for maximal flexibility and many optional connectors and other features on-board, whereas a computer to be used in a multimedia system may need to be optimized for heat and size, with additional plug-in cards being less common. The smallest motherboards may sacrifice CPU flexibility in favor of a fixed manufacturer's choice.

DVD

2007-09-27T05:14:00.000-07:00

Size comparison: A 12 cm Sony DVD+RW and a 19 cm Dixon Ticonderoga pencil.

DVD (also known as "Digital Versatile Disc" and "Digital Video Disc") is a popular optical disc storage media format used for data storage. Its main uses are for movies, software, and data archiving. Most DVDs are of the same dimensions as compact discs (CDs) but store more than 6 times the data.

The term DVD is used in describing three ways that data is stored on the disks — DVD-ROM has data which can only be read and not written, DVD-R can be written once and then functions as a DVD-ROM, and DVD-RAM holds data that can be re-written multiple times.

DVD-Video and DVD-Audio discs respectively refer to properly formatted and structured video and audio content. Everything else, including other types of DVD discs with video content, is referred to as a DVD-Data disc. DVD is also used generically to refer to HD (High Density) video disc formats Blu-ray and HD DVD.

History

In the early 1990s two high-density optical storage standards were being developed; one was the MultiMedia Compact Disc, backed by Philips and Sony, and the other was the Super Density disc, supported by Toshiba, Time Warner, Matsushita Electric, Hitachi, Mitsubishi Electric, Pioneer, Thomson, and JVC. IBM's president, Lou Gerstner, acting as a matchmaker, led an effort to unite the two camps behind a single standard, anticipating a repeat of the costly videotape format war between VHS, Betamax and Video 2000 in the 1980s.

Philips and Sony abandoned their MultiMedia Compact Disc and fully agreed upon Toshiba's SuperDensity Disc with only one modification, namely changing to EFMPlus modulation. EFMPlus was chosen as it has a great resilience against disc damage such as scratches and fingerprints. EFMPlus, created by Kees Immink, who also designed EFM, is 6% less efficient than the modulation technique originally used by Toshiba, which resulted in a capacity of 4.7 GB as opposed to the original 5 GB. The result was the DVD specification, finalized for the DVD movie player and DVD-ROM computer applications in December 1995. In May 1997, the DVD Consortium was replaced by the DVD Forum, which is open to all other companies.

Etymology

"DVD" was originally used as an initialism for the unofficial term "digital videodisk".It was reported in 1995, at the time of the specification finalization, that the letters officially stood for "digital versatile disc" (due to non-video applications),however, the text of the press release announcing the specification finalization only refers to the technology as "DVD", making no mention of what (if anything) the letters stood for.A newsgroup FAQ written by Jim Taylor (a prominent figure in the industry) claims that four years later, in 1999, the DVD Forum stated that the format name was simply the three letters "DVD" and did not stand for anything. The official DVD specification documents have never defined DVD. Usage in the present day varies, with "DVD", "Digital Video Disc", and "Digital Versatile Disc" all being common.

DVD-Video

DVD-Video is a standard for storing video content on DVD media. In the U.S., weekly DVD-Video rentals first out-numbered weekly VHS cassette rentals in June 2003, illustrating the rapid adoption rate of the technology in the marketplace.

Though many resolutions and formats are supported, most consumer DVD-Video disks use either 4:3 or 16:9 aspect ratio MPEG-2 video, stored at a resolution of 720×480 (NTSC) or 720×576 (PAL). Audio is commonly stored using the Dolby Digital (AC-3), Digital Theater System (DTS) formats, ranging from monaural to 5.1 channel "Surround Sound" presentations, and/or MPEG-1 Layer 2. Although the specifications for video and audio requirements vary by global region and television system, many DVD players support all possible formats. DVD-Video also supports features like menus, selectable subtitles, multiple camera angles, and multiple audio tracks.

DVD-Audio

DVD-Audio is a format for delivering high-fidelity audio content on a DVD. It offers many channel configuration options (from mono to 5.1 surround sound) at various sampling frequencies. Compared with the CD format, the much higher capacity DVD format enables the inclusion of either considerably more music (with respect to total running time and quantity of songs) or far higher audio quality (reflected by higher linear sampling rates and higher vertical bit-rates, and/or additional channels for spatial sound reproduction).

Despite DVD-Audio's superior technical specifications, there is debate as to whether the resulting audio enhancements are distinguishable to typical human ears. DVD-Audio currently forms a niche market, probably due to its dependency upon new and relatively expensive equipment.

Security

DVD-Audio discs employ a robust copy prevention mechanism, called Content Protection for Prerecorded Media (CPPM) developed by the 4C group (IBM, Intel, Matsushita, and Toshiba).

To date, CPPM has not been "broken" in the sense that DVD-Video's CSS has been broken, but ways to circumvent it have been developed. By modifying commercial DVD(-Audio) playback software to write the decrypted and decoded audio streams to the hard disk, users can, essentially, extract content from DVD-Audio discs much in the same way they can from DVD-Video discs.

Computer software

2007-09-27T04:46:00.000-07:00

Computer software is a general term used to describe a collection of computer programs, procedures and documentation that perform some task on a computer system. The term includes application software such as word processors which perform productive tasks for users, system software such as operating systems, which interface with hardware to provide the necessary services for application software, and middleware which controls and co-ordinates distributed systems.

Terminology

The term "software" is sometimes used in a broader context to describe any electronic media content which embodies expressions of ideas such as film, tapes, records, etc.

Relationship to computer hardware

Computer software is so called in contrast to computer hardware, which encompasses the physical interconnections and devices required to store and execute (or run) the software. In computers, software is loaded into RAM and executed in the central processing unit. At the lowest level, software consists of a machine language specific to an individual processor. A machine language consists of groups of binary values signifying processor instructions (object code), which change the state of the computer from its preceding state. Software is an ordered sequence of instructions for changing the state of the computer hardware in a particular sequence. It is usually written in high-level programming languages that are easier and more efficient for humans to use (closer to natural language) than machine language. High-level languages are compiled or interpreted into machine language object code. Software may also be written in an assembly language, essentially, a mnemonic representation of a machine language using a natural language alphabet. Assembly language must be assembled into object code via an assembler.

The term "software" was first used in this sense by John W. Tukey in 1958 In computer science and software engineering, computer software is all computer programs. The concept of reading different sequences of instructions into the memory of a device to control computations was invented by Charles Babbage as part of his difference engine. The theory that is the basis for most modern software was first proposed by Alan Turing in his 1935 essay Computable numbers with an application to the Entscheidungsproblem.

Types

Practical computer systems divide software systems into three major classes: system software, programming software and application software, although the distinction is arbitrary, and often blurred.

System software helps run the computer hardware and computer system. It includes operating systems, device drivers, diagnostic tools, servers, windowing systems, utilities and more. The purpose of systems software is to insulate the applications programmer as much as possible from the details of the particular computer complex being used, especially memory and other hardware features, and such accessory devices as communications, printers, readers, displays, keyboards, etc.
Programming software usually provides tools to assist a programmer in writing computer programs and software using different programming languages in a more convenient way. The tools include text editors, compilers, interpreters, linkers, debuggers, and so on. An Integrated development environment (IDE) merges those tools into a software bundle, and a programmer may not need to type multiple commands for compiling, interpreter, debugging, tracing, and etc., because the IDE usually has an advanced graphical user interface, or GUI.
Application software allows end users to accomplish one or more specific (non-computer related) tasks. Typical applications include industrial automation, business software, educational software, medical software, databases, and computer games. Businesses are probably the biggest users of application software, but almost every field of human activity now uses some form of application software. It is used to automate all sorts of functions.

Program and library

A program may not be sufficiently complete for execution by a computer. In particular, it may require additional software from a software library in order to be complete. Such a library may include software components used by stand-alone programs, but which cannot work on their own. Thus, programs may include standard routines that are common to many programs, extracted from these libraries. Libraries may also include 'stand-alone' programs which are activated by some computer event and/or perform some function (e.g., of computer 'housekeeping') but do not return data to their calling program. Programs may be called by one to many other programs; programs may call zero to many other programs.

Three layers

Starting in the 1980s, application software has been sold in mass-produced packages through retailers.

Users often see things differently than programmers. People who use modern general purpose computers (as opposed to embedded systems, analog computers, supercomputers, etc.) usually see three layers of software performing a variety of tasks: platform, application, and user software.

Platform software

Platform includes the firmware, device drivers, an operating system, and typically a graphical user interface which, in total, allow a user to interact with the computer and its peripherals (associated equipment). Platform software often comes bundled with the computer. On a PC you will usually have the ability to change the platform software.

Application software

Application software or Applications are what most people think of when they think of software. Typical examples include office suites and video games. Application software is often purchased separately from computer hardware. Sometimes applications are bundled with the computer, but that does not change the fact that they run as independent applications. Applications are almost always independent programs from the operating system, though they are often tailored for specific platforms. Most users think of compilers, databases, and other "system software" as applications.

User-written software

User software tailors systems to meet the users specific needs. User software include spreadsheet templates, word processor macros, scientific simulations, and scripts for graphics and animations. Even email filters are a kind of user software. Users create this software themselves and often overlook how important it is. Depending on how competently the user-written software has been integrated into purchased application packages, many users may not be aware of the distinction between the purchased packages, and what has been added by fellow co-workers.

Operation

Computer software has to be "loaded" into the computer's storage (such as a hard drive, memory, or RAM). Once the software is loaded, the computer is able to execute the software. Computers operate by executing the computer program. This involves passing instructions from the application software, through the system software, to the hardware which ultimately receives the instruction as machine code. Each instruction causes the computer to carry out an operation -- moving data, carrying out a computation, or altering the control flow of instructions.

Data movement is typically from one place in memory to another. Sometimes it involves moving data between memory and registers which enable high-speed data access in the CPU. Moving data, especially large amounts of it, can be costly. So, this is sometimes avoided by using "pointers" to data instead. Computations include simple operations such as incrementing the value of a variable data element. More complex computations may involve many operations and data elements together.

Instructions may be performed sequentially, conditionally, or iteratively. Sequential instructions are those operations that are performed one after another. Conditional instructions are performed such that different sets of instructions execute depending on the value(s) of some data. In some languages this is known as an "if" statement. Iterative instructions are performed repetitively and may depend on some data value. This is sometimes called a "loop." Often, one instruction may "call" another set of instructions that are defined in some other program or module. When more than one computer processor is used, instructions may be executed simultaneously.

A simple example of the way software operates is what happens when a user selects an entry such as "Copy" from a menu. In this case, a conditional instruction is executed to copy text from data in a 'document' area residing in memory, perhaps to an intermediate storage area known as a 'clipboard' data area. If a different menu entry such as "Paste" is chosen, the software may execute the instructions to copy the text from the clipboard data area to a specific location in the same or another document in memory.

Depending on the application, even the example above could become complicated. The field of software engineering endeavors to manage the complexity of how software operates. This is especially true for software that operates in the context of a large or powerful computer system.

Currently, almost the only limitations on the use of computer software in applications is the ingenuity of the designer/programmer. Consequently, large areas of activities (such as playing grand master level chess) formerly assumed to be incapable of software simulation are now routinely programmed. The only area that has so far proved reasonably secure from software simulation is the realm of human art— especially, pleasing music and literature.

Kinds of software by operation: computer program as executable, source code or script, configuration.

Population Health

2007-09-27T04:32:00.000-07:00

Population health is an approach to health that aims to improve the health of an entire population. One major step in achieving this aim is to reduce health inequities among population groups. Population health seeks to step beyond the individual-level focus of mainstream medicine and public health by addressing a broad range of factors that impact health on a population-level, such as environment, social structure, resource distribution, etc. An important theme in population health is importance of social determinants of health and the relatively minor impact that medicine and healthcare have on improving health overall.

From a population health perspective, health has been defined not simply as a state free from disease but as "the capacity of people to adapt to, respond to, or control life's challenges and changes" (Frankish et al., 1996).

Income inequality and mortality in 282 metropolitan areas of the United States. Mortality is correlated with both income and inequality.

Recently, there has been increasing interest from epidemiologists on the subject of economic inequality and its relation to the health of populations. There is a very robust correlation between socioeconomic status and health. This correlation suggests that it is not only the poor who tend to be sick when everyone else is healthy, but that there is a continual gradient, from the top to the bottom of the socioeconomic ladder, relating status to health. This phenomenon is often called the "SES Gradient". Lower socioeconomic status has been linked to chronic stress, heart disease, ulcers, type 2 diabetes, rheumatoid arthritis, certain types of cancer, and premature aging.

Despite the reality of the SES Gradient, there is debate as to its cause. A number of researchers (A. Leigh, C. Jencks, A. Clarkwest - see also Russell Sage working papers) see a definite link between economic status and mortality due to the greater economic resources of the better-off, but they find little correlation due to social status differences.

Other researchers such as Richard Wilkinson, J. Lynch , and G.A. Kaplan have found that socioeconomic status strongly affects health even when controlling for economic resources and access to health care. Most famous for linking social status with health are the Whitehall studies - a series of studies conducted on civil servants in London. The studies found that, despite the fact that all civil servants in England have the same access to health care, there was a strong correlation between social status and health. The studies found that this relationship stayed strong even when controlling for health-affecting habits such as exercise, smoking and drinking. Furthermore, it has been noted that no amount of medical attention will help decrease the likelihood of someone getting type 1 diabetes or rheumatoid arthritis - yet both are more common among populations with lower socioeconomic status. Lastly, it has been found that amongst the wealthiest quarter of countries on earth (a set stretching from Luxembourg to Slovakia) there is no relation between a country's wealth and general population health - suggesting that past a certain level, absolute levels of wealth have little impact on population health, but relative levels within a country do.

The concept of psychosocial stress attempts to explain how psychosocial phenomenon such as status and social stratification can lead to the many diseases associated with the SES Gradient. Higher levels of economic inequality tend to intensify social hierarchies and generally degrades the quality of social relations - leading to greater levels of stress and stress related diseases. Richard Wilkinson found this to be true not only for the poorest members of society, but also for the wealthiest. Economic inequality is bad for everyone's health.

Inequality does not only affect the health of human populations. David H. Abbott at the Wisconsin National Primate Research Center found that among many primate species, less egalitarian social structures correlated with higher levels of stress hormones among socially subordinate individuals. Research by Robert Sapolsky of Stanford University provides similar findings.

Public Health

2007-09-27T04:30:00.000-07:00

Public health is concerned with threats to the overall health of a community based on population health analysis. Health is defined and promoted differently by many organizations. The World Health Organization, the United Nations body that sets standards and provides global surveillance of disease, defines health as: "A state of complete physical, mental and social well-being and not merely the absence of disease or infirmity." Public health experts agree that nutritional, spiritual, and intellectual aspects also affect an individual's health.

The population in question can be as small as a handful of people or as large as all the inhabitants of several continents (for instance, in the case of a pandemic). Public health has many sub-fields, but is typically divided into the categories of epidemiology, biostatistics and health services. Environmental, social and behavioral health, and occupational health, are also important fields in public health.

An alternative definition by Winslow from Modern Medicine in 1920 is: "the science and art of preventing disease, prolonging life and promoting health through the organised efforts and informed choices of society, organisations, public and private, communities and individuals."

Objectives

The focus of a public health intervention is to prevent rather than treat a disease through surveillance of cases and the promotion of healthy behaviors. In addition to these activities, in many cases treating a disease can be vital to preventing it in others, such as during an outbreak of an infectious disease. Vaccination programs and distribution of condoms are examples of public health measures.

Most countries have their own government public health agencies, sometimes known as ministries of health, to respond to domestic health issues. In the United States, the frontline of public health initiatives are state and local health departments. The United States Public Health Service (PHS), led by the Surgeon General of the United States, and the Centers for Disease Control and Prevention, headquartered in Atlanta and a part of the PHS, are involved with several international health activities, in addition to their national duties.

There is a vast discrepancy in access to healthcare and public health intiatives between developed nations and developing nations. In the developing world, public health infrastructures are still forming. There may not be enough trained health workers or monetary resources to provide even a basic level of medical care and disease prevention. As a result, a large majority of disease and mortality in the developing world results from and contributes to extreme poverty. For example, many African governments spend less than USD$10 per person per year on healthcare, while, in the United States, the federal government spent approximately USD$4,500 per capita in 2000.

Many diseases are preventable through simple, non-medical methods. Public health plays a very important role in prevention efforts in both the developing world and in developed countries, either through local health systems or through international non-governmental organizations.

The two major postgraduate professional degrees related to this field are the Master of Public Health (MPH) or the (much rarer) Doctor of Public Health (DrPH). Many public health researchers hold PhDs in their fields of speciality, while some public health programs confer the equivalent Doctor of Science degree instead. The United States medical residency specialty is General Preventive Medicine and Public Health.

History of public health

In some ways, public health is a modern concept, although it has roots in antiquity. From the beginnings of human civilization, it was recognized that polluted water and lack of proper waste disposal spread vector-borne diseases. Early religions attempted to regulate behavior that specifically related to health, from types of food eaten, to regulating certain indulgent behaviors, such as drinking alcohol or sexual relations. The establishment of governments placed responsibility on leaders to develop public health policies and programs in order to gain some understanding of the causes of disease and thus ensure social stability prosperity, and maintain order.

Early public health interventions

By Roman times, it was well understood that proper diversion of human waste was a necessary tenet of public health in urban areas. The Chinese developed the practice of variolation following a smallpox epidemic around 1000 BC. An individual without the disease could gain some measure of immunity against it by inhaling the dried crusts that formed around lesions of infected individuals. Also, children were protected by inoculating a scratch on their forearms with the pus from a lesion. This practice was not documented in the West until the early-1700s, and was used on a very limited basis. The practice of vaccination did not become prevalent until the 1820s, following the work of Edward Jenner to treat smallpox.

During the 14th century Black Death in Europe, it was believed that removing bodies of the dead would further prevent the spread of the bacterial infection. This did little to stem the plague, however, which was most likely spread by rodent-borne fleas. Burning parts of cities resulted in much greater benefit, since it destroyed the rodent infestations. The development of quarantine in the medieval period helped mitigate the effects of other infectious diseases. However, according to Michel Foucault, the plague model of governmentality was later controverted by the cholera model. A Cholera pandemic devastated Europe between 1829 and 1851, and was first fought by the use of what Foucault called "social medicine", which focused on flux, circulation of air, location of cemeteries, etc. All those concerns, born of the miasma theory of disease, were mixed with urbanistic concerns for the management of populations, which Foucault designated as the concept of "biopower". The German conceptualized this in the Polizeiwissenschaft ("Science of police").

The science of epidemiology was founded by John Snow's identification of a polluted public water well as the source of an 1854 cholera outbreak in London. Dr. Snow believed in the germ theory of disease as opposed to the prevailing miasma theory. Although miasma theory correctly teaches that disease is a result of poor sanitation, it was based upon the prevailing theory of spontaneous generation. Germ theory developed slowly: despite Anton van Leeuwenhoek's observations of Microorganisms, (which are now known to cause many of the most common infectious diseases) in the year 1680 , the modern era of public health did not begin until the 1880s, with Robert Koch's germ theory and Louis Pasteur's production of artificial vaccines.

Modern public health

As the prevalence of infectious diseases in the developed world decreased through the 20th century, public health began to put more focus on chronic diseases such as cancer and heart disease.

In America, public health worker Dr. Sara Josephine Baker lowered the infant mortality rate using preventative methods. She established many programs to help the poor in New York City keep their infants healthy. Dr. Baker led teams of nurses into the crowded neighborhoods of Hell's Kitchen and taught mothers how to dress, feed, and bathe their babies. After WWI many states and countries followed her example in order to lower infant mortality rates.

During the 20th century, the dramatic increase in average life span is widely credited to public health achievements, such as vaccination programs and control of infectious diseases, effective safety policies such as motor-vehicle and occupational safety, improved family planning, fluoridation of drinking water, anti-smoking measures, and programs designed to decrease chronic disease.

Meanwhile, the developing world remained plagued by largely preventable infectious diseases, exacerbated by malnutrition and poverty. Front-page headlines continue to present society with public health issues on a daily basis: emerging infectious diseases such as SARS, making its way from China to Canada and the United States; prescription drug benefits under public programs such as Medicare; the increase of HIV-AIDS among young heterosexual women and its spread in South Africa; the increase of childhood obesity and the concomitant increase in type II diabetes among children; the impact of adolescent pregnancy; and the ongoing social, economic and health disasters related to the 2005 Tsunami and Hurricane Katrina in 2006. These are all ongoing public health challenges.

Since the 1980s, the growing field of population health has broadened the focus of public health from individual behaviors and risk factors to population-level issues such as inequality, poverty, and education. Modern public health is often concerned with addressing determinants of health across a population, rather than advocating for individual behaviour change. There is a recognition that our health is affected by many factors including where we live, genetics, our income, our educational status and our social relationships - these are known as "social determinants of health." A social gradient in health runs through society, with those that are poorest generally suffering the worst health. However even those in the middle classes will generally have worse health outcomes than those of a higher social stratum (WHO, 2003). The new public health seeks to address these health inequalities by advocating for population-based policies that improve the health of the whole population in an equitable fashion.

The burden of treating conditions caused by unemployment, poverty, unfit housing and environmental pollution have been calculated to account for between 16-22% of the clinical budget of the British National Health Service.

UK Public health functions include: • Health surveillance, monitoring and analysis • Investigation of disease outbreaks, epidemics and risk to health • Establishing, designing and managing health promotion and disease prevention programmes • Enabling and empowering communities to promote health and reduce inequalities • Creating and sustaining cross-Government and intersectoral partnerships to improve health and reduce inequalities •Ensuring compliance with regulations and laws to protect and promote health • Developing and maintaining a well-educated and trained, multi-disciplinary public health workforce • Ensuring the effective performance of NHS services to meet goals in improving health, preventing disease and reducing inequalities • Research, development, evaluation and innovation • Quality assuring the public health function

Public health programs

Today, most governments recognize the importance of public health programs in reducing the incidence of disease, disability, and the effects of aging, although public health generally receives significantly less government funding compared with medicine. In recent years, public health programs providing vaccinations have made incredible strides in promoting health, including the eradication of smallpox, a disease that plagued humanity for thousands of years.

One of the most important public health issues facing the world currently is HIV/AIDS. Tuberculosis, which claimed the lives of authors Franz Kafka and Charlotte Brontë, and composer Franz Schubert, among others, is also reemerging as a major concern due to the rise of HIV/AIDS-related infections and the development of tuberculin strains that are resistant to standard antibiotics.

Another major public health concern is diabetes. In 2006, according to the World Health Organization, at least 171 million people worldwide suffered from diabetes. Its incidence is increasing rapidly, and it is estimated that by the year 2030, this number will double.

A controversial aspect of public health is the control of smoking. Many nations have implemented major initiatives to cut smoking, such as increased taxation and bans on smoking in some or all public places. Proponents argue by presenting evidence that smoking is one of the major killers in all developed countries, and that therefore governments have a duty to reduce the death rate, both through limiting passive (second-hand) smoking and by providing fewer opportunities for smokers to smoke. Opponents say that this undermines individual freedom and personal responsibility (often using the phrase nanny state in the UK), and worry that the state may be emboldened to remove more and more choice in the name of better population health overall. However, proponents counter that inflicting disease on other people via passive smoking is not a human right, and in fact smokers are still free to smoke in their own homes.

Economics of public health

The application of economics to the realm of public health has been rising in importance since the 1980s. Economic studies can show, for example, where limited public resources might best be spent to save lives or cause the greatest increase in quality of life.

Diabetes Mellitus

2007-09-27T04:27:00.000-07:00

Diabetes mellitus, often simply diabetes (IPA pronunciation or often is a metabolic disorder characterized by hyperglycemia (high blood sugar) resulting from low levels of the hormone insulin or resistance to insulin's effects. The characteristic symptoms are polyuria (excessive urine production), polydipsia (thirst and increased fluid intake) and blurred vision; these symptoms may be absent if the blood sugar is only mildly elevated.

The World Health Organization recognizes three main forms of diabetes mellitus: type 1, type 2, and gestational diabetes (occurring during pregnancy), which have similar signs, symptoms, and consequences, but different causes and population distributions. Ultimately, all forms are due to the beta cells of the pancreas being unable to produce sufficient insulin to prevent hyperglycemia. Type 1 diabetes is usually due to autoimmune destruction of the pancreatic beta cells which produce insulin. Type 2 diabetes is characterized by insulin resistance in target tissues, but some impairment of beta cell function is necessary for its development. Gestational diabetes is similar to type 2 diabetes, in that it involves insulin resistance; the hormones of pregnancy can cause insulin resistance in women genetically predisposed to developing this condition.

Type 1 and 2 diabetes are incurable chronic conditions, but have been treatable since insulin became medically available in 1921. Type 1 diabetes, in which insulin is not secreted by the pancreas, is directly treatable only with injected or inhaled insulin, although dietary and other lifestyle adjustments are part of management. Type II may be managed uwith a combination of dietary treatment, tablets and injections and, frequently, insulin supplementation. While insulin was originally produced from natural sources such as porcine pancreas, most insulin used today is produced through genetic engineering, either as a direct copy of human insulin, or human insulin with modified molecules that provide different onset and duration of action. Insulin can also be delivered continuously by a pump surgically embedded under the skin.
Gestational diabetes typically resolves with delivery of the child.
Diabetes can cause many complications. Acute complications (hypoglycemia, ketoacidosis or nonketotic hyperosmolar coma) may occur if the disease is not adequately controlled. Serious long-term complications include cardiovascular disease (doubled risk), chronic renal failure (diabetic nephropathy is the main cause of dialysis in developed world adults), retinal damage (which can lead to blindness and is the most significant cause of adult blindness in the non-elderly in the developed world), nerve damage (of several kinds), and microvascular damage, which may cause erectile dysfunction (impotence) and poor healing. Poor healing of wounds, particularly of the feet, can lead to gangrene which can require amputation — the leading cause of non-traumatic amputation in adults in the developed world. Adequate treatment of diabetes, as well as increased emphasis on blood pressure control and lifestyle factors (such as not smoking and keeping a healthy body weight), may improve the risk profile of most aforementioned complications.

Classification
Type 1 diabetes mellitus
Type 1 diabetes mellitus—formerly known as insulin-dependent diabetes (IDDM), childhood diabetes or also known as juvenile diabetes, is characterized by loss of the insulin-producing beta cells of the islets of Langerhans of the pancreas leading to a deficiency of insulin. It should be noted that there is no known preventative measure that can be taken against type 1 diabetes. Most people affected by type 1 diabetes are otherwise healthy and of a healthy weight when onset occurs. Diet and exercise cannot reverse or prevent type 1 diabetes. Sensitivity and responsiveness to insulin are usually normal, especially in the early stages. This type comprises up to 10% of total cases in North America and Europe, though this varies by geographical location. This type of diabetes can affect children or adults but was traditionally termed "juvenile diabetes" because it represents a majority of cases of diabetes affecting children.
The main cause of beta cell loss leading to type 1 diabetes is a T-cell mediated autoimmune attack.[2] The principal treatment of type 1 diabetes, even from the earliest stages, is replacement of insulin. Without insulin, ketosis and diabetic ketoacidosis can develop and coma or death will result.
Currently, type 1 diabetes can be treated only with insulin, with careful monitoring of blood glucose levels using blood testing monitors. Emphasis is also placed on lifestyle adjustments (diet and exercise). Apart from the common subcutaneous injections, it is also possible to deliver insulin by a pump, which allows continuous infusion of insulin 24 hours a day at preset levels and the ability to program doses (a bolus) of insulin as needed at meal times. An inhaled form of insulin, Exubera, was approved by the FDA in January 2006.
Type 1 treatment must be continued indefinitely. Treatment does not impair normal activities, if sufficient awareness, appropriate care, and discipline in testing and medication is taken. The average glucose level for the type 1 patient should be as close to normal (80–120 mg/dl, 4–6 mmol/l) as possible. Some physicians suggest up to 140–150 mg/dl (7-7.5 mmol/l) for those having trouble with lower values, such as frequent hypoglycemic events. Values above 200 mg/dl (10 mmol/l) are often accompanied by discomfort and frequent urination leading to dehydration. Values above 300 mg/dl (15 mmol/l) usually require immediate treatment and may lead to ketoacidosis. Low levels of blood glucose, called hypoglycemia, may lead to seizures or episodes of unconsciousness.

Type 2 diabetes mellitus
Type 2 diabetes mellitus—previously known as adult-onset diabetes, maturity-onset diabetes, or non-insulin-dependent diabetes mellitus (NIDDM)—is due to a combination of defective insulin secretion and insulin resistance or reduced insulin sensitivity (defective responsiveness of tissues to insulin), which almost certainly involves the insulin receptor in cell membranes. In the early stage the predominant abnormality is reduced insulin sensitivity, characterized by elevated levels of insulin in the blood. At this stage hyperglycemia can be reversed by a variety of measures and medications that improve insulin sensitivity or reduce glucose production by the liver, but as the disease progresses the impairment of insulin secretion worsens, and therapeutic replacement of insulin often becomes necessary. There are numerous theories as to the exact cause and mechanism for this resistance, but central obesity (fat concentrated around the waist in relation to abdominal organs, and not subcutaneous fat, it seems) is known to predispose individuals for insulin resistance, possibly due to its secretion of adipokines (a group of hormones) that impair glucose tolerance. Abdominal fat is especially active hormonally. Obesity is found in approximately 55% of patients diagnosed with type 2 diabetes.[4] Other factors include aging (about 20% of elderly patients are diabetic in North America) and family history (type 2 is much more common in those with close relatives who have had it), although in the last decade it has increasingly begun to affect children and adolescents[citation needed], likely in connection with the greatly increased childhood obesity[citation needed] seen in recent decades in some places.

Type 2 diabetes may go unnoticed for years in a patient before diagnosis, as visible symptoms are typically mild or non-existent, usually without ketoacidotic episodes, and can be sporadic as well. However, severe long-term complications can result from unnoticed type 2 diabetes, including renal failure due to diabetic nephropathy, vascular disease (including coronary artery disease), vision damage due to diabetic retinopathy, loss of sensation or pain due to diabetes neuropathy, liver damage from non-alcoholic steatohepatitis, etc.
Type 2 diabetes is usually first treated by attempts to change physical activity (generally an increase is desired), the diet (generally to decrease carbohydrate intake), and weight loss. These can restore insulin sensitivity, even when the weight loss is modest, for example, around 5 kg (10 to 15 lb), most especially when it is in abdominal fat deposits. Some type 2 diabetics can achieve satisfactory glucose control, sometimes for years, as a result. However, the underlying tendency to insulin resistance is not lost, and so attention to diet, exercise, and weight loss must continue. The usual next step, if necessary, is treatment with oral antidiabetic drugs. As insulin production is initially only moderately impaired in type 2 diabetics, oral medication (often used in various combinations) can still be used to improve insulin production (e.g., sulfonylureas), to regulate inappropriate release of glucose by the liver (and attenuate insulin resistance to some extent (e.g., metformin), and to substantially attenuate insulin resistance (e.g., thiazolidinediones). According to one study, overweight patients treated with metformin compared with diet alone, had relative risk reductions of 32% for any diabetes endpoint, 42% for diabetes related death and 36% for all cause mortality and stroke.[5] When oral medications fail (cessation of beta cell insulin secretion is not uncommon amongst Type 2s), insulin therapy will be necessary to maintain normal or near normal glucose levels.

Gestational diabetes
Gestational diabetes also involves a combination of inadequate insulin secretion and responsiveness, resembling type 2 diabetes in several respects. It develops during pregnancy and may improve or disappear after delivery. Even though it may be transient, gestational diabetes may damage the health of the fetus or mother, and about 20%–50% of women with gestational diabetes develop type 2 diabetes later in life.
Gestational diabetes mellitus (GDM) occurs in about 2%–5% of all pregnancies. It is temporary and fully treatable but, if untreated, may cause problems with the pregnancy, including macrosomia (high birth weight), fetal malformation and congenital heart disease. It requires careful medical supervision during the pregnancy.
Fetal/neonatal risks associated with GDM include congenital anomalies such as cardiac, central nervous system, and skeletal muscle malformations. Increased fetal insulin may inhibit fetal surfactant production and cause respiratory distress syndrome. Hyperbilirubinemia may result from red blood cell destruction. In severe cases, perinatal death may occur, most commonly as a result of poor placental profusion due to vascular impairment. Induction may be indicated with decreased placental function. Cesarean section may be performed if there is marked fetal distress or an increased risk of injury associated with macrosomia, such as shoulder dystocia.
Other types
There are several rare causes of diabetes mellitus that do not fit into type 1, type 2, or gestational diabetes:
Genetic defects in beta cells (autosomal or mitochondrial)
Genetically-related insulin resistance, with or without lipodystrophy (abnormal body fat deposition)
Diseases of the pancreas (e.g. chronic pancreatitis, cystic fibrosis)
Hormonal defects
Chemicals or drugs
The tenth version of the International Statistical Classification of Diseases (ICD-10) contained a diagnostic entity named "malnutrition-related diabetes mellitus" (MRDM or MMDM, ICD-10 code E12). A subsequent WHO 1999 working group recommended that MRDM be deprecated, and proposed a new taxonomy for alternative forms of diabetes. Classifications of non-type 1, non-type 2, non-gestational diabetes remains controversial.
Signs and symptoms
The classical triad of diabetes symptoms is polyuria (frequent urination), polydipsia (increased thirst and consequent increased fluid intake), polyphagia (increased appetite). Weight loss may occur, more commonly in type 1 diabetes. These symptoms may develop quite fast in type 1, particularly in children (weeks or months) but may be subtle or completely absent—as well as developing much more slowly—in type 2. In type 1 there may also be weight loss (despite normal or increased eating) and irreducible fatigue. These symptoms may also manifest in type 2 diabetes in patients whose diabetes is poorly controlled.
When the glucose concentration in the blood is high (i.e., above the "renal threshold"), reabsorption of glucose in the proximal renal tubuli is incomplete, and part of the glucose remains in the urine (glycosuria). This increases the osmotic pressure of the urine and thus inhibits the resorption of water by the kidney, resulting in an increased urine production (polyuria) and an increased fluid loss. Lost blood volume will be replaced osmotically from water held in body cells, causing dehydration and increased thirst.
Prolonged high blood glucose causes glucose absorption and so leads to changes in the shape of the lenses of the eyes, leading to vision changes. Blurred vision is a common complaint leading to a diabetes diagnosis; type 1 should always be suspected in cases of rapid vision change whereas type 2 is generally more gradual, but should still be suspected.
Patients (usually with type 1 diabetes) may also present with diabetic ketoacidosis (DKA), an extreme state of metabolic dysregulation eventually characterized by the smell of acetone on the patient's breath, Kussmaul breathing (a rapid, deep breathing), polyuria, nausea, vomiting and abdominal pain, and any of many altered states of consciousness or arousal (e.g., hostility and mania or, equally, confusion and lethargy). In severe DKA, coma (unconsciousness) may follow, progressing to death. In any form, DKA is a medical emergency and requires hospital admission.
A rarer, but equally severe, possibility is hyperosmolar nonketotic state, which is more common in type 2 diabetes, and is mainly the result of dehydration due to loss of body water. Often, the patient has been drinking extreme amounts of sugar-containing drinks, leading to a vicious circle in regard to the water loss.
Genetics
Both type 1 and type 2 diabetes are at least partly inherited. Type 1 diabetes appears to be triggered by some (mainly viral) infections, or in a less common group, by stress or environmental exposure (such as exposure to certain chemicals or drugs). There is a genetic element in individual susceptibility to some of these triggers which has been traced to particular HLA genotypes (i.e., the genetic "self" identifiers relied upon by the immune system). However, even in those who have inherited the susceptibility, type 1 diabetes mellitus seems to require an environmental trigger. A small proportion of people with type 1 diabetes carry a mutated gene that causes maturity onset diabetes of the young (MODY).
There is a stronger inheritance pattern for type 2 diabetes. Those with first-degree relatives with type 2 have a much higher risk of developing type 2, increasing with the number of those relatives. Concordance among monozygotic twins is close to 100%, and about 25% of those with the disease have a family history of diabetes. Candidate genes include KCNJ11 (potassium inwardly rectifying channel, subfamily J, member 11), which encodes the islet ATP-sensitive potassium channel Kir6.2, and TCF7L2 (transcription factor 7–like 2), which regulates proglucagon gene expression and thus the production of glucagon-like peptide-1.[2] Moreover, obesity (which is an independent risk factor for diabetes) is strongly inherited.
Wolfram's syndrome - Wolfram's syndrome is an autosomal recessive neurodegenerative disorder that first becomes evident in childhood. It consists of diabetes insipidus, diabetes mellitus, optic atrophy, and deafness, hence the acronym DIDMOAD. Various other hereditary conditions may feature diabetes (e.g. myotonic dystrophy, Friedreich's ataxia).
Pathophysiology
Because insulin is the principal hormone that regulates uptake of glucose into most cells from the blood (primarily muscle and fat cells, but not central nervous system cells), deficiency of insulin or the insensitivity of its receptors plays a central role in all forms of diabetes mellitus.
Much of the carbohydrate in food is converted within a few hours to the monosaccharide glucose, the principal carbohydrate found in blood. Some carbohydrates are not converted. Notable examples include fruit sugar (fructose) that is usable as cellular fuel, but it is not converted to glucose and does not participate in the insulin/glucose metabolic regulatory mechanism; additionally, the carbohydrate cellulose (though it is actually many glucose molecules in long chains) is not converted to glucose, as humans and many animals have no digestive pathway capable of handling cellulose. Insulin is released into the blood by beta cells (β-cells) in the pancreas in response to rising levels of blood glucose (e.g., after a meal). Insulin enables most body cells (about 2/3 is the usual estimate, including muscle cells and adipose tissue) to absorb glucose from the blood for use as fuel, for conversion to other needed molecules, or for storage. Insulin is also the principal control signal for conversion of glucose (the basic sugar used for fuel) to glycogen for internal storage in liver and muscle cells. Reduced glucose levels result both in the reduced release of insulin from the beta cells and in the reverse conversion of glycogen to glucose when glucose levels fall, although only glucose thus recovered by the liver re-enters the bloodstream as muscle cells lack the necessary export mechanism.
Higher insulin levels increase many anabolic ("building up") processes such as cell growth and duplication, protein synthesis, and fat storage. Insulin is the principal signal in converting many of the bidirectional processes of metabolism from a catabolic to an anabolic direction, and vice versa. In particular, it is the trigger for entering or leaving ketosis (the fat burning metabolic phase).
If the amount of insulin available is insufficient, if cells respond poorly to the effects of insulin (insulin insensitivity or resistance), or if the insulin itself is defective, glucose will not be handled properly by body cells (about ⅔ require it) or stored appropriately in the liver and muscles. The net effect is persistent high levels of blood glucose, poor protein synthesis, and other metabolic derangements, such as acidosis.

Diagnosis
Diagnostic approach
Diagnostic criteria
Diabetes mellitus is characterized by recurrent or persistent hyperglycemia, and is diagnosed by demonstrating any one of the following:
fasting plasma glucose level at or above 126 mg/dL (7.0 mmol/l).
plasma glucose at or above 200 mg/dL (11.1 mmol/l) two hours after a 75 g oral glucose load as in a glucose tolerance test.
random plasma glucose at or above 200 mg/dL (11.1 mmol/l).
A positive result, in the absence of clinical symptoms of diabetes, should be confirmed by another of the above-listed methods on a different day. Most physicians prefer measuring a fasting glucose level because of the ease of measurement and the considerable time commitment of formal glucose tolerance testing, which takes two hours to complete. By current definition, two fasting glucose measurements above 126 mg/dL (7.0 mmol/l) is considered diagnostic for diabetes mellitus.
Patients with fasting sugars between 110 and 125 mg/dL (6.1 and 7.0 mmol/l) are considered to have "impaired fasting glycemia" and patients with plasma glucose at or above 140mg/dL or 7.8 mmol/l two hours after a 75 g oral glucose load are considered to have "impaired glucose tolerance". "Prediabetes" is either impaired fasting glucose or impaired glucose tolerance; the latter in particular is a major risk factor for progression to full-blown diabetes mellitus as well as cardiovascular disease.
While not used for diagnosis, an elevated level of glucose irreversibly bound to hemoglobin (termed glycosylated hemoglobin or HbA1c) of 6.0% or higher (the 2003 revised U.S. standard) is considered abnormal by most labs; HbA1c is primarily used as a treatment-tracking test reflecting average blood glucose levels over the preceding 90 days (approximately). However, some physicians may order this test at the time of diagnosis to track changes over time. The current recommended goal for HbA1c in patients with diabetes is <7.0%,>

Terminology
The term diabetes was coined by Aretaeus of Cappadocia. It is derived from the Greek word διαβαίνειν, diabaínein that literally means "passing through," or "siphon", a reference to one of diabetes' major symptoms—excessive urine production. In 1675, Thomas Willis added the word mellitus, from the Latin meaning "honey", a reference to the sweet taste of the urine. This sweet taste had been noticed in urine by the ancient Greeks, Chinese, Egyptians, and Indians. In 1776, Matthew Dobson confirmed that the sweet taste was because of an excess of a kind of sugar in the urine and blood of people with diabetes.
The ancient Indians tested for diabetes by observing whether ants were attracted to a person's urine, and called the ailment "sweet urine disease" (Madhumeha). The Korean, Chinese, and Japanese words for diabetes are based on the same ideographs which mean "sugar urine disease".
Diabetes, without qualification, usually refers to diabetes mellitus, but there are several rarer conditions also named diabetes. The most common of these is diabetes insipidus (insipidus meaning "without taste" in Latin) in which the urine is not sweet; it can be caused by either kidney (nephrogenic DI) or pituitary gland (central DI) damage.
The term "type 1 diabetes" has universally replaced several former terms, including childhood-onset diabetes, juvenile diabetes, and insulin-dependent diabetes. "Type 2 diabetes" has also replaced several older terms, including adult-onset diabetes, obesity-related diabetes, and non-insulin-dependent diabetes. Beyond these numbers, there is no agreed-upon standard nomenclature. Various sources have defined "type 3 diabetes" as, among others, gestational diabetes,[10] insulin-resistant type 1 diabetes (or "double diabetes"), type 2 diabetes which has progressed to require injected insulin, and latent autoimmune diabetes of adults (or LADA or "type 1.5" diabetes).

History
Although diabetes has been recognized since antiquity, and treatments of various efficacy have been known in various regions since the Middle Ages, and in legend for much longer, pathogenesis of diabetes has only been understood experimentally since about 1900.[11] The discovery of a role for the pancreas in diabetes is generally ascribed to Joseph von Mering and Oskar Minkowski, who in 1889 found that dogs whose pancreas was removed developed all the signs and symptoms of diabetes and died shortly afterwards.[12] In 1910, Sir Edward Albert Sharpey-Schafer suggested that people with diabetes were deficient in a single chemical that was normally produced by the pancreas—he proposed calling this substance insulin, from the Latin insula, meaning island, in reference to the insulin-producing islets of Langerhans in the pancreas.
The endocrine role of the pancreas in metabolism, and indeed the existence of insulin, was not further clarified until 1921, when Sir Frederick Grant Banting and Charles Herbert Best repeated the work of Von Mering and Minkowski, and went further to demonstrate they could reverse induced diabetes in dogs by giving them an extract from the pancreatic islets of Langerhans of healthy dogs. Banting, Best, and colleagues (especially the chemist Collip) went on to purify the hormone insulin from bovine pancreases at the University of Toronto. This led to the availability of an effective treatment—insulin injections—and the first patient was treated in 1922. For this, Banting and laboratory director MacLeod received the Nobel Prize in Physiology or Medicine in 1923; both shared their Prize money with others in the team who were not recognized, in particular Best and Collip. Banting and Best made the patent available without charge and did not attempt to control commercial production. Insulin production and therapy rapidly spread around the world, largely as a result of this decision.
The distinction between what is now known as type 1 diabetes and type 2 diabetes was first clearly made by Sir Harold Percival (Harry) Himsworth, and published in January 1936.[14]
Despite the availability of treatment, diabetes has remained a major cause of death. For instance, statistics reveal that the cause-specific mortality rate during 1927 amounted to about 47.7 per 100,000 population in Malta.
Other landmark discoveries include:
identification of the first of the sulfonylureas in 1942
reintroduction of the use of biguanides for Type 2 diabetes in the late 1950s. The initial phenformin was withdrawn worldwide (in the U.S. in 1977) due to its potential for sometimes fatal lactic acidosis and metformin was first marketed in France in 1979, but not until 1994 in the US.
the determination of the amino acid sequence of insulin (by Sir Frederick Sanger, for which he received a Nobel Prize)
the radioimmunoassay for insulin, as discovered by Rosalyn Yalow and Solomon Berson (gaining Yalow the 1977 Nobel Prize in Physiology or Medicine)[16]
the three-dimensional structure of insulin (PDB 2INS)
Dr Gerald Reaven's identification of the constellation of symptoms now called metabolic syndrome in 1988
demonstration that intensive glycemic control in type 1 diabetes reduces chronic side effects more as glucose levels approach 'normal' in a large longitudinal study,[17] and also in type 2 diabetics in other large studies
identification of the first thiazolidinedione as an effective insulin sensitizer during the 1990s
Complications
The complications of diabetes are far less common and less severe in people who have well-controlled blood sugar levels.[18][19] In fact, the better the control, the lower the risk of complications. Hence, patient education, understanding, and participation is vital. Healthcare professionals treating diabetes also often attempt to address health issues that may accelerate the deleterious effects of diabetes. These include smoking (stopping), elevated cholesterol levels (control or reduction with diet, exercise or medication), obesity (even modest weight loss can be beneficial), high blood pressure (exercise or medication if needed), and lack of regular exercise.
Acute complications
Diabetic ketoacidosis
Diabetic ketoacidosis (DKA) is an acute, dangerous complication and is always a medical emergency. Lack of insulin causes the liver to turn fat into ketone bodies, a fuel mainly for the brain. Large concentration of ketone bodies in the blood decreases the blood's pH, leading to most of the symptoms of DKA. On presentation at hospital, the patient in DKA is typically dehydrated and breathing both fast and deeply. Abdominal pain is common and may be severe. The level of consciousness is typically normal until late in the process, when lethargy (dulled or reduced level of alertness or consciousness) may progress to coma. Ketoacidosis can become severe enough to cause hypotension, shock, and death. Prompt proper treatment usually results in full recovery, though death can result from inadequate treatment, delayed treatment or from a variety of complications. Ketoacidosis occurs in type 1 and type 2 but is much more common in type 1

Nonketotic hyperosmolar coma
While not generally progressing to coma, this hyperosmolar nonketotic state (HNS) is another acute problem associated with diabetes mellitus. It has many symptoms in common with DKA, but an entirely different cause, and requires different treatment. In anyone with very high blood glucose levels (usually considered to be above 300 mg/dl (16 mmol/l)), water will be osmotically drawn out of cells into the blood. The kidneys will also be "dumping" glucose into the urine, resulting in concomitant loss of water, and causing an increase in blood osmolality. If fluid is not replaced (by mouth or intravenously), the osmotic effect of high glucose levels combined with the loss of water will eventually result in very high serum osmolality (i.e. dehydration). The body's cells will become progressively dehydrated as water is taken from them and excreted. Electrolyte imbalances are also common, and dangerous. This combination of changes, especially if prolonged, will result in symptoms of lethargy (dulled or reduced level of alertness or consciousness) and may progress to coma. As with DKA urgent medical treatment is necessary, especially volume replacement. This is the 'diabetic coma' which more commonly occurs in type 2 diabetics.

Hypoglycemia
Hypoglycemia, or abnormally low blood glucose, is a complication of several diabetes treatments. It may develop if the glucose intake does not cover the treatment. The patient may become agitated, sweaty, and have many symptoms of sympathetic activation of the autonomic nervous system resulting in feelings similar to dread and immobilized panic. Consciousness can be altered, or even lost, in extreme cases, leading to coma and/or seizures, or even brain damage and death. In patients with diabetes, this can be caused by several factors, such as too much or incorrectly timed insulin, too much exercise or incorrectly timed exercise (exercise decreases insulin requirements) or not enough food (actually an insufficient amount of glucose-producing carbohydrates in food). In most cases, hypoglycemia is treated with sugary drinks or food. In severe cases, an injection of glucagon (a hormone with the opposite effects of insulin) or an intravenous infusion of glucose is used for treatment, but usually only if the person is unconscious. In hospital, intravenous dextrose is often used.
Diabetic foot
Persons with poorly controlled diabetes often heal slowly, even from small cuts, abrasions, blisters, or separated callus (corns). The underlying cause of this healing problem is impaired circulation, which in diabetics is usually adequate to support normal tissue function but which may be inadequate for the additional circulation required to support tissue healing. In such cases, the damage, if unnoticed, left untreated, or failing to heal, can result in an infection. The resulting infection, in extreme cases, can necessitate to amputation.

Chronic complications
Vascular disease
Chronic elevation of blood glucose level leads to damage of blood vessels (angiopathy). The endothelial cells lining the blood vessels take in more glucose than normal, since they don't depend on insulin. They then form more surface glycoproteins than normal, and cause the basement membrane to grow thicker and weaker. In diabetes, the resulting problems are grouped under "microvascular disease" (due to damage to small blood vessels) and "macrovascular disease" (due to damage to the arteries).
The damage to small blood vessels leads to a microangiopathy, which can cause one or more of the following:
Diabetic retinopathy, growth of friable and poor-quality new blood vessels in the retina as well as macular edema (swelling of the macula), which can lead to severe vision loss or blindness. Retinal damage (from microangiopathy) makes it the most common cause of blindness among non-elderly adults in the US.
Diabetic neuropathy, abnormal and decreased sensation, usually in a 'glove and stocking' distribution starting with the feet but potentially in other nerves, later often fingers and hands. When combined with damaged blood vessels this can lead to diabetic foot (see below). Other forms of diabetic neuropathy may present as mononeuritis or autonomic neuropathy. Diabetic amyotrophy is muscle weakness due to neuropathy.
Diabetic nephropathy, damage to the kidney which can lead to chronic renal failure, eventually requiring dialysis. Diabetes mellitus is the most common cause of adult kidney failure worldwide in the developed world.
Macrovascular disease leads to cardiovascular disease, to which accelerated atherosclerosis is a contributor:
Coronary artery disease, leading to angina or myocardial infarction ("heart attack")
Stroke (mainly the ischemic type)
Peripheral vascular disease, which contributes to intermittent claudication (exertion-related leg and foot pain) as well as diabetic foot.
Diabetic myonecrosis ('muscle wasting')
Diabetic foot, often due to a combination of neuropathy and arterial disease, may cause skin ulcer and infection and, in serious cases, necrosis and gangrene. It is the most common cause of adult amputation, usually of toes and or feet, in the developed world.
Carotid artery stenosis does not occur more often in diabetes, and there appears to be a lower prevalence of abdominal aortic aneurysm. However, diabetes does cause higher morbidity, mortality and operative risks with these conditions.
Treatment and management
Diabetes mellitus is currently a chronic disease, without a cure, and medical emphasis must necessarily be on managing/avoiding possible short-term as well as long-term diabetes-related problems. There is an exceptionally important role for patient education, dietetic support, sensible exercise, self glucose monitoring, with the goal of keeping both short-term blood glucose levels, and long term levels as well, within acceptable bounds. Careful control is needed to reduce the risk of long term complications. This can be achieved with combinations of diet, exercise and weight loss (type 2), various oral diabetic drugs (type 2 only), and insulin use (type 1 and increasingly for type 2 not responding to oral medication). In addition, given the associated higher risks of cardiovascular disease, lifestyle modifications should be undertaken to control blood pressure and cholesterol by exercising more, smoking cessation, consuming an appropriate diet, wearing diabetic socks, and if necessary, taking any of several drugs to reduce pressure.
In countries using a general practitioner system, such as the United Kingdom, care may take place mainly outside hospitals, with hospital-based specialist care used only in case of complications, difficult blood sugar control, or research projects. In other circumstances, general practitioners and specialists share care of a patient in a team approach. Optometrists, podiatrists/chiropodists, dietitians, physiotherapists, clinical nurse specialists (eg, Certified Diabetes Educators), or nurse practitioners may jointly provide multidisciplinary expertise. In countries where patients must provide their own health care, the impact of out-of-pocket costs of diabetic care can be high. In addition to the medications and supplies needed, patients are often advised to receive regular consultation from a physician (eg, at least every three months).
Curing diabetes
Type 1 diabetes
There is no practical cure now for type 1 diabetes. The fact that type 1 diabetes is due to the failure of one of the cell types of a single organ with a relatively simple function (i.e. the failure of the islets of Langerhans) has led to the study of several possible schemes to cure this form diabetes mostly by replacing the pancreas or just the beta cells. Only those type 1 diabetics who have received a kidney-pancreas transplant (when they have developed diabetic nephropathy) and become insulin-independent may now be considered "cured" from their diabetes. Still, they generally remain on long-term immunosuppressive drugs and there is a possibility that the immune system will mount a host versus graft response against the transplanted organ.
Transplants of exogenous beta cells have been performed experimentally in both mice and humans, but this measure is not yet practical in regular clinical practice. Thus far, like any such transplant, it has provoked an immune reaction and long-term immunosuppressive drugs will be needed to protect the transplanted tissue. An alternative technique has been proposed to place transplanted beta cells in a semi-permeable container, isolating and protecting them from the immune system. Stem cell research has also been suggested as a potential avenue for a cure since it may permit regrowth of Islet cells which are genetically part of the treated individual, thus perhaps eliminating the need for immuno-suppressants. A 2007 trial of 15 newly diagnosed patients with type 1 diabetes treated with stem cells raised from their own bone marrow after immune suppression showed that the majority did not require any insulin treatment for prolonged periods of time.
Microscopic or nanotechnological approaches are under investigation as well, in one proposed case with implanted stores of insulin metered out by a rapid response valve sensitive to blood glucose levels. At least two approaches have been demonstrated in vitro. These are, in some sense, closed-loop insulin pumps.
Type 2 diabetes
Type 2 diabetes can be cured by gastric bypass surgery in 80-100% of obese patients, and in some non-obese patients, usually within days after surgery. This is not an effect of weight loss, since it occurs long before weight loss. After gastric bypass surgery for obesity, the death rate from all causes is reduced by up to 40%
Prevention
Type 1 diabetes risk is known to depend upon a genetic predisposition based on HLA types (particularly types DR3 and DR4), an unknown environmental trigger, and an uncontrolled autoimmune response which attacks the insulin producing beta cells. Research from the 1980s suggested that breastfeeding decreased the risk, various other nutritional risk factors are being studied, but few have a strong link with the development of type 1 diabetes.
Type 2 diabetes risk can be reduced in many cases by making changes in diet and increasing physical activity.[30][31] A review article by the American Diabetes Association[32] recommends maintaining a healthy weight, getting at least 2½ hours of exercise per week (marathon intensity or duration is not needed; a brisk sustained walk appears sufficient), have a modest fat intake, and eating a good amount of fiber and whole grains. Magnesium may play a significant role in preventing Type 2 diabetes.[33] Although they do not recommend alcohol consumption as a preventative, they note that moderate alcohol intake (at or below one ounce of alcohol per day depending on body mass) may reduce the risk. They state that there is not enough consistent evidence that eating foods of low glycemic index is helpful, but nutritious, low glycemic-index (low carbohydrate) foods are encouraged. (It should be noted that many low-GI foods are not recommended, for various reasons.
Some studies have shown delayed progression to diabetes in predisposed patients through the use of metformin,[31] rosiglitazone, or valsartan. In patients on hydroxychloroquine for rheumatoid arthritis, incidence of diabetes was reduced by 77%. Breastfeeding might also be correlated with the prevention of type 2 of the disease in mothers.
As of late 2006, although there are many claims of nutritional cures, there is no credible demonstration for any. In addition, despite claims by some that vaccinations (eg, as for childhood diseases) may cause diabetes, there are no studies proving any such connection.
Aging
According to the American Diabetes Association, approximately 18.3% (8.6 million) of Americans age 60 and older have diabetes. [38] Diabetes mellitus prevalence increases with age, and the numbers of older persons with diabetes are expected to grow as the elderly population increases in number. The National Health and Nutrition Examination Survey (NHANES III) demonstrated that, in the population over 65 years old, 18% to 20% have diabetes, with 40% having either diabetes or its precursor form of impaired glucose tolerance.
The way diabetes is managed changes with age. Insulin production decreases because of the age-related impairment of pancreatic beta cells. Insulin resistance increases due to the loss of lean tissue and the accumulation of fat, particularly intra-abdominal fat, and the decreased tissue sensitivity to insulin. Glucose tolerance progressively declines with age, and there is a high prevalence of type 2 diabetes and postchallenge hyperglycemia in the older population. Age-related glucose intolerance in humans is often accompanied by insulin resistance, but circulating insulin levels are similar to those of younger people.
Researchers and clinicians agree that treatment goals for older patient with diabetes need to be individualized and take into account health status, as well as life expectancy, level of dependence, and willingness to adhere to a treatment regimen. Following evaluation, one of two levels of care can be recommended: symptom-preventing care or aggressive care. The decision is made jointly by the patient and the primary caregiver.

Public health and policy
The 1989 Declaration of St Vincent was the result of international efforts to improve the care accorded to those with diabetes. Doing so is important both in terms of quality of life and life expectancy but also economically - expenses to diabetes have been shown to be a major drain on health- and productivity-related resources for healthcare systems and governments.
Several countries established more and less successful national diabetes programmes to improve treatment of the disease.
Epidemiology and statistics
In 2006, according to the World Health Organization, at least 171 million people worldwide suffer from diabetes. Its incidence is increasing rapidly, and it is estimated that by the year 2030, this number will double. Diabetes mellitus occurs throughout the world, but is more common (especially type 2) in the more developed countries. The greatest increase in prevalence is, however, expected to occur in Asia and Africa, where most patients will likely be found by 2030. The increase in incidence of diabetes in developing countries follows the trend of urbanization and lifestyle changes, perhaps most importantly a "Western-style" diet. This has suggested an environmental (i.e., dietary) effect, but there is little understanding of the mechanism(s) at present, though there is much speculation, some of it most compellingly presented.
Diabetes is in the top 10, and perhaps the top 5, of the most significant diseases in the developed world, and is gaining in significance there and elsewhere (see big killers).
For at least 20 years, diabetes rates in North America have been increasing substantially. In 2005 there are about 20.8 million people with diabetes in the United States alone. According to the American Diabetes Association, there are about 6.2 million people undiagnosed and about 41 million people that would be considered prediabetic.[45] However, the criteria for diagnosing diabetes in the USA means that it is more readily diagnosed than in some other countries. The Centers for Disease Control has termed the change an epidemic. The National Diabetes Information Clearinghouse estimates that diabetes costs $132 billion in the United States alone every year. About 5%–10% of diabetes cases in North America are type 1, with the rest being type 2. The fraction of type 1 in other parts of the world differs; this is likely due to both differences in the rate of type 1 and differences in the rate of other types, most prominently type 2. Most of this difference is not currently understood. The American Diabetes Association point out the 2003 assessment of the National Center for Chronic Disease Prevention and Health Promotion (Centers for Disease Control and Prevention) that 1 in 3 Americans born after 2000 will develop diabetes in their lifetime.

Environmental Health

2007-09-27T04:18:00.000-07:00

Environmental health is the branch of public health that is concerned with all aspects of the natural and built environment that may affect human health. Other terms that refer to the discipline of environmental health include environmental public health and environmental health and protection.

Environmental health practitioners may be known as sanitarians, public health inspectors, environmental health specialists or environmental health officers.

Nutrition and Health

There are six main nutrients that the body needs to receive: carbohydrates, proteins, fats, vitamins, minerals, and water. It is important to consume these six nutrients on a daily basis to build and maintain healthy body systems.

Ill health can be caused by an imbalance of nutrients, producing either an excess or deficiency, which in turn affects body functioning cumulatively. Moreover, because most nutrients are, in some way or another, involved in cell-to-cell signalling (e.g. as building block or part of a hormone or signalling 'cascades'), deficiency or excess of various nutrients affects hormonal function indirectly. Thus, because they largely regulate the expression of genes, hormones represent a link between nutrition and how our genes are expressed, i.e. our phenotype. The strength and nature of this link are continually under investigation, but observations especially in recent years have demonstrated a pivotal role for nutrition in hormonal activity and function and therefore in health.

Soil contamination is the presence of man made chemicals or other alteration to the natural soil environment. This type of contamination typically arises from rupture of underground storage tanks, application of pesticides, percolation of contaminated surface water to subsurface strata, leaching of wastes from landfills or direct discharge of industrial wastes to the soil. The most common chemicals involved are petroleum hydrocarbons, solvents, pesticides, lead and other heavy metals. This occurrence of this phenomenon is correlated with the degree of industrialization and intensity of chemical usage.

The concern over soil contamination stems primarily from health risks, both of direct contact and from secondary contamination of water supplies

Health effects

The major concern is that there are many sensitive land uses where people are in direct contact with soils such as residences, parks, schools and playgrounds. Other contact mechanisms include contamination of drinking water or inhalation of soil contaminants which have vaporized. There is a very large set of health consequences from exposure to soil contamination depending on pollutant type, pathway of attack and vulnerability of the exposed population. Chromium and many of the pesticide and herbicide formulations are carcinogenic to all populations. Lead is especially hazardous to young children, in which group there is a high risk of developmental damage to the brain and nervous system, while to all populations kidney damage is a risk.

Chronic exposure to benzene at sufficient concentrations is known to be associated with higher incidence of leukemia. Mercury and cyclodienes are known to induce higher incidences of kidney damage, some irreversible. PCBs and cyclodienes are linked to liver toxicity. Organophosphates and carbamates can induce a chain of responses leading to neuromuscular blockage. Many chlorinated solvents induce liver changes, kidney changes and depression of the central nervous system. There is an entire spectrum of further health effects such as headache, nausea, fatigue, eye irritation and skin rash for the above cited and other chemicals. At sufficient dosages a large number of soil contaminants cause death.

Drinking water is water that is intended to be ingested by humans. Water of drinkable qaulity is termed potable water, whether it is used as such or not. Although many fresh water sources are utilised by humans, some contain disease or pathogens and cause long-term health problems if they do not meet specific water quality guidelines. Water that is not harmful for human beings is sometimes called safe water, water which is not contaminated to the extent of being unhealthful. The available supply of drinking water is an important criterion of carrying capacity, the population level that can be supported by planet Earth.

As of the year 2006 (and pre-existing for at least three decades), there is a substantial shortfall in availability of potable water, primarily arising from overpopulation in lesser developed countries. Many nations have water quality regulations for water sold as drinking water, although these are often not strictly enforced outside of the developed world. The World Health Organization sets international standards for drinking water.

Environmental health services

Environmental health services are defined by the World Health Organization as:

those services which implement environmental health policies through monitoring and control activities. They also carry out that role by promoting the improvement of environmental parameters and by encouraging the use of environmentally friendly and healthy technologies and behaviours. They also have a leading role in developing and suggesting new policy areas.

Environmental Tobacco Smoke (ETS), is a serious and deadly environmental health issue facing workers across the world. On June 27, 2006, the U.S. Surgeon General released an in-depth report which analyzed the body of science relating to the disease and death caused by secondhand smoke.

Sanitary sewer overflow (SSO) is a condition whereby untreated sewage is discharged into the environment, escaping wastewater treatment. This situation, also known as Wet Weather Overflow, is primarily meaningful in developed countries, which have extensive sewage treatment facilities. The main causes of SSO are:

Infiltration of excessive stormwater into sewer lines during heavy rainfall
Rupture or blockage of sewerage lines
Malfunction of pumping station lifts or electrical power failure
Human operator error at treatment plant facilities

Since a number of countries have essentially 100 percent treatment of domestic wastewater, an SSO episode is viewed as a significant breakdown in environmental control of water resources; for example, the USA, Japan, the United Kingdom and some other European countries strive for complete secondary treatment of all effluent and pursue vigorously shortcomings in the sewerage systems.

By far the most prevalent cause of Sanitary Sewer Overflow stems from heavy rainfall events which can cause massive infiltration of stormwater into sewerage lines. This circumstance is most prevalent in older cities whose subsurface infrastructure is quite old; Inflow into the sanitary lines can be caused by tree root rupture of subsurface lines or by mechanical fracture due to age and overpressure from trucks and buildings above.

Other modes of system failure can include power outage which may disable lift station pumps or parts of the treatment plant operations themselves; in fact, any mechanical system failure within a treatment plant can create a circumstance leading to overflow: breakdown of rotating arms of trickling filters, jamming of line gates, clogging of filters or grates etc. Furthermore, some forms of human error can infrequently lead to diversion of sewage and result in an overflow event.

Decentralized failures in dry weather mainly occur from collection sewer line blockages, which can arise from a debris clog, line rupture or tree root intrusion into the line itself. One of the main problems of a decentralized line failure is the difficulty of defining the location of overflow, since a typical urban system contains thousands of miles of collection pipage, and the central treatment plant has no way of communicating with all the lines, unless expensive monitoring equipment has been installed.

Human health and ecological consequences

Human health impacts include significant numbers of gastrointestinal illness each year, although death from one overflow event is uncommon. Additional human impacts include beach closures, swimming restrictions and prohibition against consumption of certain aquatic animals (particularly certain molluscs) after overflow events. Ecological consequences include fish kills, harm to plankton and other aquatic microflora and microfauna. Turbidity increase and dissolved oxygen decrease in receiving waters can lead to accentuated effects beyond the obvious pathogenic induced damage to aquatic ecosystems. It is possible that higher life forms such as marine mammals can be affected since certain seals and sea lions are known to experience peaks in pathogenic harm