| | | |  CMOS | | | | Complementary Metal Oxide Semiconductor. This term, "metal oxide semiconductor" refers to the physical structure found in some field effect transistors - a metal gate electrode set on top of an oxide insulator, on top of a semiconducting material. A very widely used silicon and germanium based integrated circuit (IC) design, almost ubiquitous across all electronic products - most modern chips (termed "die" or "dice" in the industry) are now constructed on the CMOS basis. The CMOS IC is a type of transistor that, unlike other transistors, uses a combination of both NMOS (negative polarity) and PMOS (positive polarity) circuits connected together. Only one of these circuit types is on at a particular time (CMOS circuits dissipate power only when switching), meaning that a CMOS chip uses less power than an equivalent NMOS or PMOS chip and is very efficient, also emitting less energy in the form of waste heat. As a result of the latter, certain CMOS chips can run very fast without risking heat damage. CMOS circuitry is more dense than other design types with the same functionality. The charge in the circuit can also stay in one state over an extended period of time. CMOS circuits also show a high level of immunity to electronic noise. All of this makes CMOS ICs ideal for use in battery powered devies such as laptop PCs and PDAs for example. CMOS memory is also used in PCs (and other devices) to store critical low-level system information such as system setup data and the time and date, where the minimal current drain on a small lithium ion "CMOS battery" on a motherboard (for example) can keep this data safe for many years. | | | | | | Virus | | | | A piece of code or a program that is able to replicate itself without the conscious intervention of the user of the "host" machine. The term is commonly used to refer to any kind of malware, however strictly speaking it means code that attaches itself to another program to replicate itself. The first viruses to be seen by home users arose in the 1980s. A man-made phenomenon, viruses are most commonly activated (statistically) when an email attachment containing one is opened and they are also spread via such methods as bootleg software or software traded illegally on file sharing networks. It may do a number of other things as well as replicating itself, including executing programs, "sending" itself to infect other recipients using the host's email client or network connection (this type of virus is usually referred to as a "worm"), deleting files or installing files. More destructive viruses can even require that the hard drive be reformatted. Even apparently benign viruses still cause a problem for the host machine however, by using up available memory. Viruses may be divided into "resident" and "non-resident" types, depending on what happens when they are executed. Resident viruses are loaded into the computer's memory when executed, upon which control is handed to the host program. The virus then spreads by attaching itself to other applications / programs when they are executed and it remains active in memory. In contrast, non-resident types immediately search for new hosts upon being executed, attach themselves to the new host and only then transfer control to the infected host program. Viruses may also be written for legitimate reasons - for testing purposes when developing antivirus software for example, or to check existing security measures. This situation differs from viruses encountered in the "wild" because the intention when writing them is not malicious. | | | | | | Gateway | | | | A software or hardware device that acts to bridge two or more networks and acts as an "entrance", allowing information to be shared between computers. Strictly, it means a hardware or software device forming a node (a "processing location" such as a PC or printer that has a unique MAC address) in a network, that connects two networks using either different protocols or different applications, however it can also refer to a device linking two similar networks in which case it acts simply as an entrance or exit point. In the former case, it converts data packets from one protocal to another and in the latter it allows the connecting networks to share information by converting data and/or commands between different formats. In general usage however, the term has come to mean any system that allows access to another. A common example of the use of a gateway in the home is an ISP connecting the user to the internet. When accessing a website from a PC data may pass through a large number of gateways in the processs. A gateway may be combined with a router and/or a switch within the same hardware device, which may be relatively inexpensive, particularly in devices intended for home use and small business networks. In the case of enterprise level business applications, it may take the form of a server acting as a gateway/node and also as a firewall and proxy server. This term used to be used to describe a router but is now obsolete in that sense. | | | |
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