Glossary of terms - Lesson 1

Boot up

Sequence of events beginning with power-on and ending with your computer ready to run applications.

Browser

Software program that is used to display and navigate through WWW (World Wide Web) pages stored in HTML format on the Internet.

central processing unit

(CPU, processor) The part of a computer which controls all the other parts. Designs vary widely but, in general, the CPU consists of the {control unit}, the {arithmetic and logic unit} (ALU) and memory ({registers}, {cache}, {RAM} and {ROM}) as well as various temporary buffers and other logic. The control unit fetches instructions from memory and decodes them to produce signals which control the other part of the computer. This may cause it to transfer data between memory and ALU or to activate {peripherals} to perform input or output. A {parallel computer} has several CPUs which may share other resources such as memory and peripherals. The term "processor" has to some extent replaced "CPU", though RAM and ROM are not normally considered as part of a processor. This is particularly true of common modern {microprocessors} though there have been microprocessors which include RAM and/or ROM on the same {integrated circuit}. The {CPU Info Center} lists many kinds of CPU. (1998-10-21)

Drive (my definition)

Technically the mechanism that spins the disks. Commonly used to refer to "disks", especially hard disks (e.g. hard drive). Drives are designated by a letter followed by a colon. Computers may have drives a: to z:, with A: and B: reserved for floppy drives, C: for the hard disk, and the remainder used for additional disk drives or peripheral devices such as CD-ROM, tape drives, or Zip Drive.

EISA

{Extended Industry-Standard Architecture}

Executable file

A program that runs when its filename is selected (Windows) or typed at the Command-line. Executable files have extensions of .exe, .com, or .bat.

expansion card

A circuit board which can be plugged into one of a computer's {expansion slots} to provide some optional extra facility such as additional {RAM}, {disk controller}, {coprocessor}, {graphics accelerator}, communication device or some special-purpose interface. Different computers have different standards for the cards they accept, e.g. {PCI}.

fixed disk

A {hard disk} which is not a {removable disk}. footprint 1. The floor or desk area taken up by a piece of hardware. 2. The amount of {disk} or {RAM} taken up by a program or file. 3. ({IBM}) The {audit trail} left by a crashed program (often "footprints"). See also {toeprint}.

Floppy disk

(Or "floppy", "diskette") A small, portable plastic disk coated in a magnetisable substance used for storing computer data, readable by a computer with a floppy disk drive. The physical size of disks has shrunk from the early 8 inch, to 5 1/4 inch ("minifloppy") to 3 1/2 inch ("microfloppy") while the data capacity has risen. These disks are known as "floppy" disks (or diskettes) because the disk is flexible and the read/write head is in physical contact with the surface of the disk in contrast to "{hard disks}" (or winchesters) which are rigid and rely on a small fixed gap between the disk surface and the heads. Floppies may be either single-sided or double-sided. 3.5 inch floppies are less floppy than the larger disks because they come in a stiff plastic "envelope" or case, hence the alternative names "stiffy" or "crunchy" sometimes used to distinguish them from the floppier kind. The following formats are used on {IBM PC}s and elsewhere:

Capacity	Density	Width
360KB	double	5.25"
720KB	double	3.5"
1.2MB	high	5.25"
1.44MB	high	3.5"

Double density and high density are usually abbreviated DD and HD. HD 3.5 inch disks have a second hole in the envelope and an overlapping "HD" logo. (1996-08-23)

Gb

Gigabit. 10^9 {bit}s. Might also be wrongly used for {gigabyte} ({GB}).

GB

{gigabytes} or {gigabits} - see {MB}. Giga stands for 10^9 - a US billion, or in computing for 2^30. The text of a thirty volume encyclopaedia would require about one gigabyte of {ASCII} storage.

gig

{gigabyte}

giga-

{prefix}

gigabyte

2^30 = 1,073,741,824 {byte}s = 1024 {megabytes}. Roughly the amount of data required to encode a human gene sequence (including all the redundant codons). See {prefix}.

graphics adaptor

(Or "graphics adapter", "graphics card", "video adaptor", etc.) A circuit board fitted to a computer, especially an {IBM PC}, containing the necessary {video memory} and other electronics to provide a {bitmap display}. Adaptors vary in the {resolution} (number of {pixels}) and number of colours they can display, and in the {refresh rate} they support. These parameters are also limited by the {monitor} to which the adaptor is connected. A number of such {display standards}, e.g. {SVGA}, have become common and different {software} requires or supports different sets.

graphics card

{graphics adaptor}

GUI

{Graphical User Interface} - Windows is a GUI, as opposed to the command line interface you saw using "command" or the Linux OS which is also command line.

hard disk

(In contrast to {floppy disk}). One or more rigid {magnetic disks} rotating about a central axle with associated read/write heads and electronics, used to store data. Most hard disks are permanently connected to the drive (fixed disks) though there are also {removable disks}. High speed disks have an {access time} of 28 milliseconds or less, and low-speed disks run 65 milliseconds or more. The higher speed disks also transfer their data faster than the slower speed units. Each surface of each disk is divided into a number of evenly spaced concentric circular {tracks}. The set of all tracks at a given radius on all surfaces (the tracks which can be accessed without moving the heads) are known as a {cylinder}. Each track is divided into {sectors}. Disk drives are commonly characterised by the kind of interface used to connect to the computer, e.g. {ATA}, {IDE}, {SCSI}.

hard disk drive

(HDD) A {disk drive} used to read and write {hard disk}s.

hard drive

{hard disk drive}

hardware

The physical, touchable, material parts of a computer or other system. The term is used to distinguish these fixed parts of a system from the more changable {software} or {data} components which it executes, stores, or carries. Computer hardware typically consists chiefly of electronic devices ({CPU}, {memory}, {display}) with some electromechanical parts (keyboard, {printer}, {disk drives}, {tape drives}, loudspeakers) for input, output, and storage, though completely non-electronic (mechanical, electromechanical, hydraulic, biological) computers have also been conceived of and built.

IBM PC

International Business Machines Personal Computer. IBM PCs and compatible models from other vendors are the most widely used computer systems in the world. They are typically single user {personal computers}, although they have been adapted into multi-user models for special applications. Note: "IBM PC" is used in this dictionary to denote IBM and compatible personal computers, and to distinguish these from other {personal computers}, though the phrase "PC" is often used elsewhere, by those who know no better, to mean "IBM PC or compatible". There are hundreds of models of IBM compatible computers. They are based on {Intel}'s {microprocessors}: {Intel 8086}, {Intel 8088}, {Intel 80286}, {Intel 80386}, {Intel 486} or {Pentium}. The models of IBM's first-generation Personal Computer (PC) series have names: IBM PC, {IBM PC XT}, {IBM PC AT}, Convertible and Portable. The models of its second generation, the Personal System/2 ({PS/2}), are known by model number: Model 25, Model 30. Within each series, the models are also commonly referenced by their {CPU} {clock rate}. All IBM personal computers are software compatible with each other in general, but not every program will work in every machine. Some programs are time sensitive to a particular speed class. Older programs will not take advantage of newer higher-resolution {display standards}. The speed of the {CPU} ({microprocessor}) is the most significant factor in machine performance. It is determined by its {clock rate} and the number of bits it can process internally. It is also determined by the number of bits it transfers across its {data bus}. The second major performance factor is the speed of the {hard disk}. {CAD} and other graphics-intensive {application programs} can be sped up with the addition of a mathematics {coprocessor}, a chip which plugs into a special socket available in almost all machines.

inkjet printer

A class of printer in which small ink droplets are sprayed electrostatically from a nozzle onto the paper. Inkjet printers are very quiet in comparison to {impact printer}s. A popular example is the {Olivetti} {BJ10}.

input device

A {peripheral} used to transfer data from the outside world into a computer system. Some input devices are operated directly by the user, e.g. {keyboard}, {mouse}, {touch screen}, {joystick}, {digitising tablet}, microphone; others are sensors or transducers which convert external signals into data, e.g. using an {ananlog to digital converter} (this would also be true of a microphone). Other kinds of inputs are really one half of a bidirectional link with another computer or storage device, e.g. {serial line}, {SCSI} interface.

input/output

(I/O) Communication between a computer and its users, its storage devices, other computers (via a {network}) or the outside world. The devices the computer uses to do this are called "{peripherals}".

I/O

{Input/Output}

ISP

Internet Service Provider. A company that provides one of the permanent links that make up the Internet and sells connections to private users and companies to allow them to access the Internet.

Jaz Drive

{Iomega Corporation}'s drive which takes removable one or two {gigabyte} disk cartridges which contain conventional {hard disks}. Internal and external drives are available claiming an average transfer rate of 330 {megabytes} per minute - though that is dependant on the {SCSI} adapter, the parallel port adapter is unlikely to reach anything like this speed. The Jaz drive was the successor to the company's more establistablished {Zip Drive}.

joystick

A device consisting of a hand held stick that pivots about one end and transmits its angle in two dimensions to a computer. Joysticks are often used to control games, and usually have one or more push-buttons whose state can also be read by the computer. Most I/O interface cards for {IBM PC}s have a joystick (game control) port.

Kb

{kilobyte}

keyboard

A {hardware} device consisting of a number of mechanical buttons (keys) which the user presses to input characters to a computer. Keyboards were originally part of {terminal}s which were separate {peripheral} devices that performed both input and output and communicated with the computer via a {serial line}. Today a keyboard is more likely to be connected directly to the processor, allowing the processor to scan it and detect which key or keys are currently pressed. Keyboards vary in the keys they have, most have keys to generate the {ASCII} {character set} as well as various {function key}s and special purpose keys, e.g. reset or volume control.

kilo-

{prefix}

kilobyte

(KB) 2^10 = 1024 {bytes}.

laptop computer

(Commonly just "laptop") A portable {personal computer} of a size suitable to rest comfortably on one's legs. A laptop is smaller than a "{luggable}" (portable, but not comfortably) but bigger than a "{palmtop}" (easily carried in one hand or a shirt pocket). {Toshiba} were one of the first companies to produce laptops, in about 1989.

laser printer

A non-impact high-resolution printer which uses a rotating disk to reflect laser beams onto the paper. When the beam touches the paper, it forms an electrostatic image area which attracts electrically-charged toner (magnetized dry ink powder). The toner is then fixed (heated) onto the paper, forming an image (text or graphics). Print resolution ranges between 300 and 600 dots per inch (DPI). Laser printers using chemical photoreproduction techniques can produce resolutions of up to 2400 DPI. Print speeds may exceed 21,000 lines per minute, though printing speed is more often given in pages per minute. If a laser printer is rated at 12 pages per minute (PPM), this figure would be true only if the printer is printing the same data on each of the twelve pages, so that the bit map is identical. This speed however, is rarely reached if each page contains different codes, text, and graphics. Although there are dozens of retail brands of laser printers, only a few {original equipment manufacturers} make {print engines}, e.g. {Canon}, {Ricoh}, {Toshiba}, and {Xerox}.

learning curve

(From psychology) A graph of some measure of something learned against time or number of trials. In computing, it is often misused to mean the amount of time it takes to learn the usage of something ("reduce the learning curve") or the ease of learning it ("easy learning curve"). Even more incorrectly, the phrase "steep learning curve" is used to mean "hard to learn" whereas of course a steep curve would indicate rapid learning.

local bus

A {bus} connecting a {processor} to {memory}, usually on the same {circuit board} as opposed to a {backplane} and therefore faster. Various proprietary local busses for {personal computers} are still in use. The most common are {Vesa local bus} (VLB or VL), and {Peripheral Component Interconnect} (PCI). Some computers, e.g. {notebook computers}, use a local bus with no expansion slots. Previous non-local bus standards include {ISA}, {EISA} and {MCA}.

LPT

/L-P-T/ or /lip'it/ or /lip-it'/ Line printer.

main memory

The storage device used by a computer to hold the currently executing program and its working data. A modern computer's main memory is built from {random access memory} {integrated circuits}. In the old days {ferrite core memory} was one popular form of main memory, leading to the use of the term "{core}" for main memory. Computers have several other sorts of memory, distinguished by their access time, storage capicity, cost, and the typical lifetime or rate of change of the data they hold. {Registers} in the {CPU} are fast, few, expensive and typically change every few machine instructions. Other kinds are {cache}, {PROM}, {magnetic disk} (which may be used for {virtual memory}), and {magnetic tape}.

MB

(Or "Mb") {megabytes} or {megabits}. When referring to the size or data transfer rate of a storage device which is accessed in multiples of eight bits (e.g. {RAM}, {hard disk}) this almost certainly means megabytes, but when referring to the data transfer rate of a communications system it probably means {megabits}. Some years ago, it is claimed, "MB" always meant megabytes and "Mb" meant megabits but recently this useful distinction has been lost.

meg

{megabyte} - approx. 1 million bytes

mega-

{prefix}

megabyte

({MB}, colloquially "meg") 2^20 = 1,048,576 {bytes} = 1024 {kilobytes}. 1024 megabytes are one {gigabyte}. The text of a six hundred page paperback book would require about a megabyte of {ASCII} storage.

memory

These days, usually used synonymously with {Random Access Memory} or {Read-Only Memory}, but in the general sense it can be any device that can hold {data} in {machine-readable} format.

memory location

A {byte}, {word} or other small unit of storage space in a computer's {main memory} that is identified by its starting {address} (and size).

MHz

{MegaHertz}

modem

(Modulator/demodulator) An electronic device for converting between serial data (typically {RS-232}) from a computer and an audio signal suitable for transmission over telephone lines. In one scheme the audio signal is composed of silence (no data) or one of two frequencies representing 0 and 1. Modems are distinguished primarily by the maximum {baud} rate they support. {Baud} rates can range from 75 baud up to 28800 and beyond. Data to the computer is sometimes at a lower rate than data from the computer on the assumption that the user cannot type more than a few characters per second. Various data {compression} and error correction {algorithm}s are required to support the highest speeds. Other optional features are {auto-dial} (auto-call) and {auto-answer} which allow the computer to initiate and accept calls without human intervention. Most modern modems support a number of different protocols and two modems, when first connected will automatically negotiate to find a common protocol. Some modem protocols allow the two modems to renegotiate ("retrain") if the initial choice of data rate is too high and gives too many transmission errors. A modem may either be internal, connected to the computer's bus or external ("stand-alone"), connected to one of the computer's {serial port}s. The actual speed of transmission in characters per second depends not just the modem-to-modem data rate, but also on the speed with which the processor can transfer data to and from the modem, the kind of compression used and whether the data is compressed by the processor or the modem, the amount of noise on the telephone line (which causes retransmissions), the serial character format (typically {8N1}: one {start bit}, eight data bits, no {parity}, one {stop bit}).

monitor

1. A {cathode-ray tube} and associated electronics connected to a computer's video output. A monitor may be either {monochrome} (black and white) or colour ({RGB}). Colour monitors may show either digital colour (each of the red, green and blue signals may be either on or off, giving eight possible colours: black, white, red, green, blue, cyan, magenta and yellow) or analog colour (red, green and blue signals are continuously variable allowing any combination to be displayed). Digital monitors are sometimes known as {TTL} because the voltages on the red, green and blue inputs are compatible with TTL logic chips.

motherboard

The main {printed circuit board} in an electronic device, particularly a computer, which contains sockets that accept additional boards ("daughter-boards"). In a (personal) computer, the motherboard contains the {bus}, the {microprocessor} and chips used for controlling any built-in {peripheral}s such as the keyboard, text and graphics display, {serial port}s and {parallel port}s, {joystick} and {mouse} {interface}s.

mouse

The most common kind of {pointing device}. A mouse is moved over a flat horizontal surface and includes some means of converting its position in two dimensions into X-Y coordinates which the computer can read. It also has one or more buttons whose state can also be read. It is called a mouse because the wire connecting it to the computer or keyboard looks like a mouse's tail. The two commonest types of mouse are rolling ball and optical. The former has a ball which rests on the surface and rotates as the mouse moves. The ball is also in contact with two shafts at right-angles to each other whose rotation is measured by optoelectronic sensors. An optical mouse has no moving parts but requires a special mouse mat (mouse mats used with rolling ball mice are optional extras to improve traction) marked with a pattern of horizontal and vertical lines. The mouse contains a {light-emitting diode} and photocells to detect the light reflected from the pattern on the mat. Some mice are shaped to fit the hand and some even come in left- and right-handed versions. A good {operating system} will specify conventions for the use of three mouse buttons. One button, as on the {Macintosh}, is far too limiting and, far from simplifying use, requires the use of modifier keys on the keyboard to accomplish tasks which could be done more simply with multiple mouse buttons.

Peripheral device

Hardware devices other than the base system of CPU, monitor, keyboard, and mouse. Includes such things as printer, CD-ROM, Scanners, and Film recorders.