Welcome to NCS

AC
Alternating Current: the common form of electricity from power plant to home/office. Its direction is reversed 60 times per second in the U.S.; 50 times in Europe. Contrast with DC.

Access
Read, write, or update information on some storage medium, such as a disk.

Access Time
Time interval between the instant that a piece of information is requested from a memory or peripheral device and the instant the information is supplied by the device. With hard disks or compact discs, maximum access time is measured as the time it takes to move from one end of the disc to the other, find a piece of information, and transfer that information to RAM.

AI
Artificial Intelligence: the branch of computer science concerned with making computers behave like humans. Applications include: games playing, expert systems, natural language and robotics. AI also implies the ability to learn or adapt through experience.

ADC
Analogue-to-Digital Converter: a device that converts continuously varying analogue signals from instruments that monitor such conditions as movement, temperature, sound, etc., into binary code for the computer. It may be contained on a single chip or can be one circuit within a chip.

ANSI American National Standards Institute. A standards-setting, non-government organisation which develops and publishes standards for voluntary use in the United States.

API Application Programming Interface: a set of subroutines or functions that a program, or application, can call to tell the operating system to perform some task. The Windows API consists of more than 1,000 functions that programs written in C, C++, Pascal, and other languages can call to create windows, open files, and perform other essential tasks.

Archive Long-term on- and/or off-site storage.

ASIC Application Specific Integrated Circuit: an integrated circuit chip designed for a particular use rather than general use. Many video boards and modems use ASICs.

ASCII American Standard Code for Information Interchange: a standard developed by the American National Standards Institute (ANSI) describing how characters can be represented on a computer. The ASCII character set consists of 128 characters numbered from 0 to 127 and includes numerals, punctuation symbols, letters, and special control codes such as end-of-line characters. Most personal computers use some form of the ASCII character set.

ASPI
Advanced SCSI Protocol Interface: an interface standard developed by Adaptec Inc. that has become one of the major SCSI interface standards for computers.

Asynchronous
Refers to events that are not synchronised, or co-ordinated, in time. Most communication between computers and devices is asynchronous - it can occur at any time and at irregular intervals.

Backup A copy of a file, directory, or volume on a separate storage device from the original, for the purpose of retrieval in case the original is accidentally erased, damaged, or destroyed.

Bandwidth The amount of data that can be moved through a particular interface in a given period of time, e.g. a 64-bit wide, 100 MHz SDRAM data bus has a bandwidth of 800MBps.

BBS Bulletin Board System: a term for dial-up on-line systems from which to download software, leave messages for other users, and exchange information. BBBs proliferated in the 1980s before the WWW became popular. A BBS functions somewhat like a stand-alone Web site, but without graphics. However, unlike Web sites, each BBS has its own telephone number to dial into.

Binary Pertaining to a number system that has just two unique digits. For most purposes, the decimal number system is used, which has ten unique digits, 0 through 9. All other numbers are then formed by combining these ten digits. Computers are based on the binary numbering system, which consists of just two unique numbers, 0 and 1. All operations that are possible in the decimal system (addition, subtraction, multiplication, division) are equally possible in the binary system.

Bit A Binary Digit is the basic binary unit for storing data. It can either be 0 or 1. It takes 8 bits to equal a byte.

Block Consists of a number of bytes. Block sizes vary, but a block size of either 512 or 1024 user data bytes is commonly used.

Boot Drive The drive that the operating system first loads from (usually :A: or :C).

Buffer An area of memory, often referred to as a 'cache', used to speed up access to devices. It is used for temporary storage of data read from or waiting to be sent to a device such as a hard disk, CD-ROM or tape drive.

Bus An electronic traffic lane through which electrical signals are carried from one chip to another chip. Most often used in the context of communication between the processor and other system components. There are many different kinds of bus including ISA, EISA, MCA and the local bus standards PCI and VL-Bus.

Byte
Eight bits treated as a unit and representing a character.

Capacity
Total amount of user data that can be stored on a device.

CCIR Consultative Committee for International Radio communications.

Clone Any computer system compatible with the IBM PC standard.

COM Port A serial port for attaching modem, plotter, printer, or mouse to a system. There are usually 2 COM port connectors: a 9-pin (DB-9) for the mouse, and a 25-pin (DB-25) for a plotter or external modem.

Crosstalk
Interference from an adjacent electronics circuitry.

DAC Digital-to-Analogue Converter: a device (usually a single chip) that converts digital data into analogue signals. Video adaptors require DACs to convert digital data to analogue signals that the monitor can process. Modems require a DAC to convert data to analogue signals that can be carried by telephone wires.

Daughter Board
A printed circuit board that plugs into another circuit board (usually the motherboard). It is similar to an expansion board, but accesses the motherboard components (memory and CPU) directly rather than through the slower expansion bus.

DC Direct Current: an electrical current that travels in one direction and used within the computer's electronic circuits. Contrast with AC.

DDE Dynamic Date Exchange: a mechanism used in Windows to transfer data between two applications or two separate instances of the same application. Windows itself uses DDE for a variety of purposes, from opening documents in running applications when a document icon is double-clicked in the shell to obtaining program icons for DOS applications. DDE is also used to support OLE. See also OLE.

Device Driver A software routine that links a peripheral device to the operating system. It acts like a translator between a device and the applications that use it. Each device has its own set of specialised commands known only to its driver. In contrast, most applications access devices by using high-level, generic commands. The driver accepts these generic and translates them into the low-level specialised commands required by the device.

DIN connector A German standard used mostly for audio applications. DIN connectors are used for keyboards, PS/2 style mice, MIDI, and Apple printer attachments.

Directory An area or data structure in which information is stored regarding the location and contents of files and/or file structures. Also called directory partition.

Drive Bay
Refers to a site in a where many mass storage devices can be internally installed. Usually a 5.25in-wide 1in-tall hole in a computer case. The number of drive bays in a computer determines how many such devices can be internally installed. The other common size is 3.5in. Bays are described as either internal or exposed. An internal bay is meant for hard disk drives, an exposed bay for removable media drives, such as a CD-ROM, tape backup or floppy disk unit. Some manufacturers use the terms hidden and accessible in place of internal and exposed.

DLL Dynamic Link Library: a special type of Windows program containing functions that other programs can call, resources (such as icons) that other programs can use, or both. Unlike a standard programming library, whose functions are linked into an application when the application's code is compiled, an application that uses functions in a DLL links with those functions at runtime - hence the term 'dynamic'.

DTR Data Transfer Rate: the speed at which data is transferred between a host and a data recording device. Usually noted in KBps or MBps, and sometimes in MB/minute. Can mean a 'peak' rather than a 'sustained' transfer rate.

Dual Boot Allows the computer to boot to two different operating systems (DOS & UNIX, for example).

Encoding A method whereby a group of data bits is translated into a group of recording bits.

ETSI European Telecommunications Standards Institute: A non-profit membership organisation founded in 1988, dedicated to standardizing telecommunications throughout Europe. It promotes worldwide standards, and its efforts are coordinated with the ITU.

EPP Enhanced Parallel Port: a parallel port that conforms to the EPP standard developed by the IEEE (Institute of Electrical and Electronics Engineers) 1284 standards committee. The EPP specification transforms a parallel port into an expansion bus that can handle up to 64 disk drives, tape drives, CD-ROM drives, and other mass-storage devices. EPPs are rapidly gaining acceptance as inexpensive means to connect portable drives to notebook computers.

Ethernet
Developed by Xerox, Digital and Intel (IEEE 802.3) , this is the most widely used LAN access method. Normally, all stations on a segment share the total bandwidth, which is either 10Mbit/s (Ethernet), 100Mbit/s (Fast Ethernet) or 1000Mbit/s (Gigabit Ethernet). With switched Ethernet, each sender and receiver pair have the full bandwidth.

Expansion Card A circuit board that fits into a computer expansion slot to add a certain function (like a modem, sound card, or SCSI interface).

FCC Federal Communications Commission: the U.S. Government agency that regulates electronic communication.

File Server A computer that provides network stations with controlled access to shareable resources. The network operating system is loaded on the file server, and most shareable devices (disk subsystems, printers) are attached to it. The file server controls system security and monitors station-to-station communications. A dedicated file server can be used only as a file server while it is on the network. A non-dedicated file server can be used simultaneously as a file server and a workstation.

Firmware Permanent instructions and data programmed directly into the circuitry of read-only memory for controlling the operation of the computer or peripheral devices. Distinct from software, which is stored in read/write memory and can be altered.

Form Factor The physical size and shape of a device. It is often used to describe the size of circuit boards. The physical size of a device as measured by outside dimensions. With regard to a disk drive, the form factor is the overall diameter of the platters and case, such as 3.5in or 5.25in, not the size in terms of storage capacity. If the drive is a 5.25in form factor it means that the drive is the same size as a 5.25in diskette drive and uses the same fixing points.

GB Gigabyte: a unit of measure consisting of 1000MB.

GBps Gigabytes per second: a performance measure used for mass storage devices and memory systems.

Gflops Gigaflops: 1 thousand million floating-point instructions per second.

GiB Gibibyte: a unit of measure consisting of 1024MiB.

GOPS
Giga Operations Per Second: in the case of multimedia processing, more GOPS translate to better video quality.

GPF General Protection Fault: the error code triggered when a Windows program causes a failure or lock-up.

Huffman Coding For a given character distribution, by assigning short codes to frequently occurring characters and longer codes to infrequently occurring characters, Huffman's minimum redundancy encoding minimises the average number of bytes required to represent the characters in a text.

HSM Hierarchical Storage Management: System of ranking and storing information across a variety of device types.

Hz Hertz: the number of times something happens a second.

IBM PC
IBM created the PC industry when it launched its first PC in 1981. They were named PC, XT, AT etc.

IC
Integrated Circuit: a tiny complex of electronic components and their connections that is produced in or on a small slice of material (as silicon).

IEEE Institute of Electrical and Electronics Engineers: a membership organisation that includes engineers, scientists and students in electronics and allied fields. Best known for its involvement in setting standards for computers and communications, such as the widely followed IEEE 802 standards for Local Area Networks.

iMac An Apple computer intended for home, school, and small offices, and promoted by Apple as an easy-to-use, stylish computer that outperforms other low-cost options. The computer comes equipped with a 233MHz G3 processor, 32 MB SDRAM, 4GB hard disk drive, a 56K modem, and a Universal Serial Bus (USB), which allows a user to add devices without restarting the computer. Controversially, the iMac does not come with a floppy disk drive. Easily recognisable for its translucent blue casing, the computer sold quickly after its introduction in the summer of 1998.

Interface A hardware or software protocol, contained in the electronics of the disk controller and disk drive, that manages the exchange of data between the drive and computer. The most common interfaces for small computer systems are AT (IDE) and SCSI.

Internet The global computer network, composed of thousands of WANs and LANs that uses TCP/IP to provide world-wide communications to homes, schools, businesses and governments. The WWW runs on the Internet.

I/O Input/Output: refers to data transfer from input devices (keyboard, mouse, scanner, etc.) to output devices (printer, screen, etc.).

I/O Address Memory location for a particular device (disk drive, sound card, printer port, etc.). Two devices cannot share the same I/O address space.

IRQ Interrupt Request: a signal from a hardware device such as a keyboard or a drive controller indicating that it needs the CPUs attention. IRQ signals are transmitted along IRQ lines, which connect peripheral devices to a programmable interrupt controller, or PIC. The PIC prioritises the incoming interrupt requests from different devices and delivers them to the CPU one at a time via a dedicated IRQ line connecting the PIC to the CPU.

ISO International Standards Organisation: an international body responsible for establishing and managing various standards committees and expert groups, including several image-compression standards.

Isochronous Refers to processes where data must be delivered within certain time constraints. For example, multimedia streams require an isochronous transport mechanism to ensure that data is delivered as fast as it is displayed and to ensure that the audio is synchronised with the video. Contrast with Asynchronous and Synchronous.

ISP
Internet Service Provider: a company that provides access to the Internet. For a monthly fee, subscribers are provided with the necessary software, a username, password and access phone number. Using a modem or ISDN terminal adaptor they can then log on to the Internet, browse and download from the WWW and send and receive e-mail. An amount of free Web space is generally provided, allowing the subscriber to create a Web site and thereby have a presence on the Web.

KB
Kilobyte: a unit of measure consisting of 1000 bytes.

KBps Kilobytes per second: a performance measure used for mass storage devices and memory systems.

Kbit Kilobit: a unit of measure consisting of 1000 bits. The unit often used in expressions of data transmission capacity.

KiB Kibibyte: a unit of measure consisting of 1024 bytes. One of the names and symbols for prefixes for binary multiples for use in the fields of data processing and data transmission approved as an IEC International Standard in December 1998. See also MiB, GiB and TiB.

LAN Local Area Network: a computer network technology designed to connect computers separated by a short distance. The local group of linked computers are generally connected to a single, shared server.

Latency
The time between initiating a request for data and the beginning of the actual data transfer.

Legacy
Term used to describe an application, architecture, protocol, system or system component etc. that has been in existence for a long time.

Low Profile Describes drives built to the 3.5in form factor, which are only 1in high. The standard form factor drives are 1.625in high.

LSI
Large Scale Integration: between 3,000 and 100,000 transistors on a chip. VLSI (Very Large Scale Integration) is between 100,000 and one million transistors on a chip.

Mac Macintosh: introduced by Apple Computer in 1984, the Macintosh marked a breakthrough in personal computer technology, featuring a graphical user interface (GUI) that utilised windows, icons and a mouse. This made it much easier for novices to use the computer productively, requiring them only to point to a selection on a menu and click a mouse button rather than learn a complex set of commands, as had previously been the case. The success of the Macintosh GUI led heralded a new age of graphics-based applications and operating systems, Microsoft's subsequent Windows interface copying many features from the Mac.

MAN
Metropolitan Area Network.

MB
Megabyte: a unit of measure consisting of 1000KB.

MBps Megabytes per second: a performance measure used for mass storage devices and memory systems.

MCI Media Control Interface: platform-independent multimedia specification published by Microsoft Corporation and others in 1990. Provides a consistent way to control devices such as CD-ROMs and video playback units.

Media
A component used to store data such as a tape or rotating disk.

Mflops Megaflops: 1 million floating-point instructions per second.

MHz Megahertz: a measurement of frequency in millions of cycles per second.

MiB Mebibyte: a unit of measure consisting of 1024KiB.

Microcode
The lowest-level instructions that directly control a microprocessor. A single machine-language instruction typically translates into several microcode instructions. In modern PC microprocessors, the microcode is hard-wired and can't be modified.

Micron (µm)
A unit of measure equivalent to one-millionth of a metre; synonymous with micrometre.

Microsecond (µs) One millionth of a second (.000001 sec.)

Millisecond (ms) One thousandth of a second (.001 sec.)

MIPS
Millions of Instructions Per Second: refers to a computer processor's performance.

MOPS
Millions of Operations Per Second.

MTBF Mean Time Between Failure: the average time a specific component is expected to work without failure.

MTTR Mean Time To Repair: the average time to repair a specific component.

Multitasking
The concurrent execution of several jobs.

Multithreading
Multiple concurrent threads of execution within a single application.

Nanometre (nm) One thousand millionth of a metre.

Nanosecond (ns) One thousand-millionths of a second of a second (.000000001 sec.). Light travels approximately 8 inches in 1 nanosecond.

Network
A group of two or more computer systems linked together. There are many types of computer networks, including LANs and WANs.

NMI
NonMaskable Interrupt: a high-priority interrupt that cannot be disabled by another interrupt. It is used to report malfunctions such as parity, bus and math co-processor errors.

Noise
Interference (static) that destroys the integrity of signals on electronic highways or communications lines. Noise can come from a variety of sources, including radio waves, nearby electrical wires, lightning, and bad connections. Noise is an analogue problem; once a signal is digitised, it is relatively immune to noise.

NOS Network Operating System.

NTFS NT File System: the file system that is native to Microsoft Windows NT. NTFS is probably the most advanced file system available for personal computers, featuring superior performance, excellent security and crash protection, and the ability to handle large volumes of data.

ODBC Open Database Connectivity: a standard promulgated by Microsoft that allows databases created by various database management programs-such as DBASE, Microsoft Access, Microsoft FoxPro, and Oracle to be accessed using a common interface independent of the database file format. By relying on ODBC, one can write an application that uses the same code to read records from a DBASE file or a FoxPro file. Internally, ODBC drivers use a form of SQL to carry out database operations. See also SQL and WOSA.

OEM Original Equipment Manufacturer: a company which develops, produces and sells computer and consumer hardware.

OLE
Object Linking and Embedding: an industry-standard method for inserting an object into a document. The document retains a connection, or link, with its original program so that double-clicking on the object in the document opens the object's original program. See also DLL.

OS
Operating system: the software controlling the overall operation of a multipurpose computer system, including such tasks as memory allocation, input and output distribution, interrupt processing, and job scheduling.

Oscilloscope A test instrument that displays electronic signals (waves and pulses) on a screen. It creates its own time base against which signals can be measured, and display frames can be frozen for visual inspection.

OSR
OEM Service Release: a version of Windows 95 incorporating bug fixes and new functionality released to PC vendors for bundling with new PCs. Not available as an upgrade to older versions of Windows 95.

PCB
Printed Circuit Board: a board upon which there are layers of printed circuits and onto which other integrated circuits can be soldered or otherwise attached.

PCMCIA Personal Computer Memory Card International Association: a consortium of computer manufacturers that devised the standard for the credit card-size adaptor cards used in many notebook computers. PCMCIA defines three card types: Type I cards can be up to 3.3mm thick and are generally used for RAM and ROM expansion cards; Type II cards can be as thick as 5.5mm and typically house modems and fax modems; Type III cards are the largest of the lot (up to 10.5mm thick) and are mostly used for solid state disks or miniature hard disks. PCMCIA cards are also known as 'PC Cards'.

PDA Personal Digital Assistant: a handheld device that combines computing, telephone/fax, and networking features. A typical PDA can function as a cellular phone, fax sender, and personal organiser. Some PDAs are hand-held PC with tiny keyboards. Another class of device uses a touch-screen and stylus for data entry.

Peripheral Any hardware device - such as a disk drive, tape drive, printer or modem - added to a system as a complement to the basic CPU.

PIC Programmable Interrupt Controller: a chip or device that prioritises interrupt requests generated by keyboards, serial ports, and other devices and passes them on to the CPU in order of highest priority. See also IRQ.

Picolitre (pl) A million millionth of a litre.

PIM Personal Information Manager: a type of software application - a given on PDA devices and many mobile phones - that allows you to enter text for any purpose and retrieve it based on any of the words you typed in. PIMs vary widely, but all of them attempt to provide methods for managing information the way you use it on a daily basis. Typical features include a telephone list, calendar, scheduler, reminder and calculation functions.

PnP Plug and Play: a Microsoft/Intel specification that allows for self-configuration of computers and peripherals. A fully Plug and Play-enabled PC requires three PnP components: a PnP BIOS, PnP adaptors and peripherals, and a PnP operating system. Adding a PnP-compliant device to a PnP PC requires little more than making the physical connection. The operating system, in conjunction with PnP logic present in the BIOS and in the device itself, handles the IRQ settings, I/O addresses, and other technical aspects of the installation to ensure that the device does not conflict with other installed devices.

Protected Mode A memory-addressing system supporting 32-bit instruction sets. I t mediates between different programs running at once, and keeps them within their memory boundaries.

Protocol A formal set of rules and descriptions of information formats that allow two computers to exchange information.

PS/2
An IBM personal computer series introduced in 1987, superseding the original PC line. It introduced the 3.5in floppy disk, VGA graphics and Micro Channel bus. The latter has since given way to the PCI bus.

Random Access Ability to access any particular block by going directly to it. Memory and disk devices support random access; by contrast, tape storage devices do not.

Real-time In computing, refers to an operating mode under which data is received and processed and the results returned so quickly as to seem instantaneous.

Removable Storage A type of storage which allows the actual storage media to be removed from a drive and replace it with other media. It is used for the transportation of data between computers and for data backup.

RPM Revolutions Per Minute.

RTF
Rich Text Format: a format in common use by word processors. It accepts both text and images, and retains text formatting and page layout.

Substrate
The base layer of a chip, printed circuit board or multichip module (MCM) onto which semiconductor devices are fabricated. Silicon is the most widely used substrate for chips. Fibreglass is mostly used for printed circuit boards, and ceramic is used for MCMs.

Synchronous
Refers to events that are synchronised, or co-ordinated, in time. Communication within a computer is usually synchronous and is governed by the microprocessor clock. Signals along the bus, for example, can occur only at specific points in the clock cycle.

SQL Structured Query Language: a query language developed by IBM that relies on simple English-language statements to perform database queries. Almost universally supported in one form or another by relational databases on platforms of all types, SQL allows databases from different manufacturers and on different types of computers to be queried using a standard syntax. See also ODBC.

TB
Terabyte: a unit of measure for storage capacity 1,000,000,000,000 (1 trillion) bytes, or 1,000,000 (1 million) megabytes or 1,000 (1 thousand) gigabytes.

TCP/IP Transmission Control Protocol/Internet Protocol: the communications protocol used by UNIX systems and the Internet. TCP checks for lost packets, puts the data from multiple packets into the correct order and requests that missing or damaged packets be resent.

TiB Tebibyte: a unit of measure consisting of 1024GiB.

Token Ring
Developed by IBM (IEEE 802.5), this is the second most widely used LAN access method (behind Ethernet). It uses a token ring access method and connects up to 255 nodes in a star topology at 4 or 16Mbit/s.

Transistor
A semiconductor device that uses a stream of charge carriers to produce active electronic effects.

UNIX A multi-user, multiprocessor operating system developed by AT&T in the early 1970s. It exists in various forms and implementations and is the predominant operating system used by the Internet servers. It is not, however, required by the user to access the Internet.

VAR Value Added Reseller: a company which resells hardware and software packages to developers and/or end-users.

WAN Wide Area Network: a geographically dispersed network formed by linking several computers or local area networks (LANs) together over long distances, usually using leased long-distance lines. WANs can connect systems across town, in different cities, or in different regions of the world.

WOSA Windows Open Services Architecture: a collection of APIs that provide standard ways for Windows applications to access databases, telephony devices, messaging services, and other services. ODBC and MAPI are two examples of APIs that fall under the WOSA umbrella.

WYSIWYG What You See Is What You Get: screen output that exactly (or very closely) matches the appearance of printed output. WYSIWYG displays were once rare on the PC platform, because most applications ran in character mode and had little control over the format of text rendered on the screen. Today WYSIWYG applications abound, because Windows allows more precise control over screen formatting and provides a device-independent interface to both screens and printers.