Communication and Network

Modulation


An earlier magnetic disk encoding method that places clock bits onto the medium along with the data bits. It was superseded by MFM and RLL. Varying the frequency of the waves of a carrier in order to transmit analog or digital data. Frequency modulation (FM) is widely used in audio transmission, not only for its namesake FM radio, but for the audio channels in television.

Demodulation

To isolate a data signal from a carrier wave. The demodulation circuit uses the unmodulated carrier as a reference signal and compares it to the received signal.

Bandwidth

The term bandwidth has a number of technical meanings but since the popularization of the Internet, it has generally referred to the volume of information per unit of time that a transmission medium (like an Internet connection) can handle.

TCP/IP
(Transmission Control Protocol/Internet Protocol) A communications protocol developed under contract from the U.S. Department of Defense to internetwork dissimilar systems. Invented by Vinton Cerf and Bob Kahn, this de facto Unix standard is the protocol of the Internet and the global standard for local area networks and wide area networks, the major exception being the traditional networks of the telephone companies.

Node

In a communications system, a node is a network junction or connection point. Every terminal, computer, hub and switch is a node. In database management, a node is an item of data that can be accessed by two or more routes. In computer graphics, a node is an endpoint of a graphical element. In the Document Object Model (DOM), which exposes HTML and XML content to an application or script, every element, every attribute of that element, and each piece of textual content for every attribute is considered a node.

Client
An architecture in which the user's PC (the client) is the requesting machine and the server is the supplying machine, both of which are connected via a local area network (LAN) or a wide area network (WAN) such as the Internet. Throughout the late 1980s and early 1990s, client/server was the hot buzzword as applications were migrated from minicomputers and mainframes with input/output terminals to networks of desktop computers.

Server

A computer that runs a Web site. Using the HTTP protocol, the Web server delivers Web pages to browsers as well as other data files to Web-based applications. The Web server includes the hardware, operating system, Web server software, TCP/IP protocols and site content (Web pages, images and other files). If the Web server is used internally and is not exposed to the public, it is an "intranet server"

Network operating System

An operating system that is designed for network use. Normally, it is a complete operating system with file, task and job management; however, with some earlier products, it was a separate component that ran under the OS; for example, LAN Server required OS/2, and LANtastic required DOS.

Server

Unix, Linux, NetWare, Windows 2000 Server and Windows Server 2003 are examples of network operating systems designed for use in stand-alone servers. Such products may also include a Web server, directory services, messaging system, network management and multiprotocol routing capabilities.

Network Administrator

A person who manages a local area communications network (LAN) or wide area network (WAN) for an organization. Responsibilities include network security, installing new hardware and applications, monitoring software upgrades and daily activity, enforcing licensing agreements, developing a storage management program and providing for routine backups, not to mention ensuring that it is up and running all the time.

Secondary Storage

Disk Caching



To store data locally in order to speed up subsequent retrievals. Reserved areas of memory in every computer that are used to speed up instruction execution, data retrieval and data updating. Pronounced "cash," they serve as staging areas, and their contents are constantly changing. There are two kinds: memory caches and disk caches.

File Compression

Encoding data to take up less storage space and less bandwidth for transmission. Digital data are compressed by finding repeatable patterns of binary 0s and 1s. The more patterns can be found, the more the data can be compressed. Text can typically be compressed to approximately 40% of its original size, and graphics files from 20% to 90%. Some files compress very little. It depends entirely on the type of file and compression algorithm used.

File Decompression

Data compression is the encoding of data to consume less space and bandwidth. Data decompression is the reverse--the decoding of compressed data to restore the original data. Compression/decompression algorithms look for redundancies in data, then minimize them using predetermined algorithms (methods). There are different algorithms used to achieve different compression rates.

Internet Hard Drive
The sole purpose of an Internet hard drive is to offer a means of accessing your computer files (pictures, documents, music, videos, etc.) from any computer, as long as that computer has access to the Internet. Similar to depositing money into your bank account, and later withdrawing that same money from any ATM machine, an Internet hard drive will allow you to "deposit" your computer files into a remote hard drive, and then later access those very same files from any other computer.

Optical Disk Drive

A direct access storage device that is written and read by light. The most common optical discs in use are CDs and DVDs, and they come in three types: read-only, write-once and rewritable. CD, CD-ROM, DVD-ROM, DVD-Video as well as BD-ROM (Blu-ray) are read-only discs that are recorded at the time of manufacture and cannot be erased. CD-R, DVD-R, DVD+R, BD-R, WORM and magneto-optic (in WORM mode) discs are write-once. They are recorded in the user's environment, but cannot be erased. CD-RW, DVD-RAM, DVD-RW, DVD+RW, BD-RE and MO discs are rewritable.

Solid-state Storage



Non mechanical. Solid state refers to electronic circuits composed of transistors, resistors, capacitors and other components, which may be discrete, single devices, or millions of them can be created in a single chip. For example, microprocessors and memories are all solid state. In a solid state device, there is no mechanical action, although an unbelievable amount of electromagnetic action takes place within.

A computer has solid state and non-solid state parts. The solid state components are the motherboard, chips, screen, camera and optical mouse, while the hard drive, CD/DVD drive, fans, keyboard, microphone, speakers and mechanical mouse are both electronic and mechanical and thus not solid state.

Input and Output

Ergonomic Keyboard

A keyboard that separates the keys into two halves shaped like a wide "V." Some keyboards have a fixed layout, while others are movable. To the touch typist, the layout feels odd at first, but it puts less stress on the hands and wrist and winds up being comfortable for most people.

Inkjet Printer

A printer that propels droplets of ink directly onto the medium. Today, almost all inkjet printers produce color. Low-end inkjets use three ink colors (cyan, magenta and yellow), but produce a composite black that is often muddy. Four-color inkjets (CMYK) use black ink for pure black printing. Inkjet printers run the gamut from less than a hundred to a couple hundred dollars for home use to tens of thousands of dollars for commercial poster printers.

Laser Printer

A laser printer is a printer that uses a focused beam or light to transfer text and images onto paper. Though contrary to popular belief, the laser does not actually burn the images onto the paper. Instead, as paper passes through the printer, the laser beam fires at the surface of a cylindrical drum called a photoreceptor. This drum has an electrical charge (typically positive), that is reversed in areas where the laser beam hits it. By reversing the charge in certain areas of the drum, the laser beam can print patterns (such as text and pictures) onto the photoreceptor.

Magnetic-Ink Character Recognition

MICR, is a character recognition technology used primarily by the banking industry to facilitate the processing of cheques The technology allows computers to read information (such as account numbers) off printed documents. Unlike barcodes or similar technologies, however, MICR codes can be easily read by humans.

Optical-Character Recognition

The machine recognition of printed characters. OCR systems can recognize many different OCR fonts, as well as typewriter and computer-printed characters. Advanced OCR systems can recognize hand printing.

Optical-Mark Recognition


The technology of electronically extracting intended data from marked fields, such as checkboxes and fill-infields, on printed forms. OMR technology scans a printed form and reads predefined positions and records where marks are made on the form. This technology is useful for applications in which large numbers of hand-filled forms need to be processed quickly and with great accuracy, such as surveys, reply cards, questionnaires and ballots.