GNVQ ITGNVQ ITOther glossaries and link pages
[General
glossary ] [ Internet General Glossary
] [ Network terms ] [Languages
Java Fact File ] [ Useful
sites ] [GNVQ
Glossary]
A BCDE
F
I MO
PRS V
Accelerator Card, in computer science, a printed circuit board that replaces or augments the computer's main microprocessor with a faster one. An accelerator card allows a user to upgrade a system to a faster microprocessor without having to replace the cards, drives, keyboard, or case. This substantially reduces the total system price. See also COMPUTER; INTEGRATED CIRCUIT; MICROCOMPUTER.
Access Time, in computer science, generally, the time required for information to be gathered from some remote source, such as data from a computer's memory or data from a hard disk. With reference to memory handling, access time is the time it takes a memory system to present information to the microprocessor after an address has been selected. Sometimes the access time is taken as measured from a particular control signal. Eg. the time between the read control line ready and data ready is called the read command access time. The memory cycle is the minimum time between two consecutive accesses
With reference to disk storage, the time required for a disk drive to respond to a request for a data read or write operation. Access time is normally measured in milliseconds (thousandths of a second) and covers the interval between the time the read/write command is issued and the time information indicating the success (or failure) of the operation is received. During this interval, the disk drive moves the read/write head over the surface of the disk to the appropriate location, settles the head into position, and waits for the appropriate sectors to rotate under the head to perform the actual read or write. Access time is often quoted for hard disks to indicate the speed at which the disk operates. The time given can be either the lowest possible access time or an average access time. Currently, an access time under 30 milliseconds is considered fast; over 60 milliseconds is considered slow. see cache architecture bus capacity cisc computer family computer coprocessor expanded memory hard drive memory access memory devices DRAM VRAM EDO RAM SRAM memory hierarchy memory organisation microprocessor pipeliningRAM RISC ROM PROM EPROM EEPROM Storage storage devices.
ADC (Acronym for Analogue-Digital-Convertor) an electronic circuit that converts an analogue signal into a digital one. Many sensors / transducers (temperature, humidity, stress, sound, light cells) are designed to produce analogue electrical signals for measurement purposes. This is often on the form of a varying voltage. A digital computer is not able to read these signals unless they are converted to a binary signal. The measuring range of a sensor is broken down into a number of discrete levels (often 256) and each level is given a binary code. An ADC will sample a signal and then allocate the equivalent binary code for the level that was measured at the time of sampling. A computer can now store the measurement and, by accepting other inputs, can either log readings, carry out mathematical calculations, or boolean operations on the data. This also allows a computer to develop programs to control physical devices.
Analogue signals can be converted to digital codes by a number of methods including integration, successive approximation, pulse code modulation .
D/A conversion is the complementary process of converting digital signals back into analogue signals.
Both A/D and D/A conversion circuits are readily available as integrated circuits (ICs) from a number of manufacturers. Although comparator ICs are also available these are for use in other situations as an A/D convertor IC will contain the relevant comparator circuits needed.
A/D and D/A convertors can also be part of larger ICs.
Architecture (computer), in computer science, a general term referring to the structure of all or part of a computer system. The term also covers the design of system software, such as the operating system, as well as referring to the combination of hardware and basic software that links the machines on a computer network. Computer architecture refers to an entire structure and to the details needed to make it functional. Thus, computer architecture covers computer systems, chips, circuits, and system programs but typically does not refer to applications, which are required to perform a task but not to make the system run.
Many computer microprocessors
have a CISC (complex instruction set computing) architecture.
RISC
(reduced instruction set computing) processors frequently use a pipeline
architecture, which fetches new processor instructions while a current
instruction is still executing. A disk subsystem that uses memory to pre
load and retain information from a disk may be said to have a cached
architecture.
see cache
architecture access time bus capacity
cisc computer family computer
co-processor expanded memory hard
drive memory access memory
devices DRAM VRAM EDO RAM
SRAM memory hierarchy
memory organisation microprocessor
pipelining
RAM RISC
ROM PROM EPROM
EEPROM Storage storage devices
Baud unit of electrical signalling speed equal to one pulse (bit) per second, used in data transmission, measuring the speed rate at which signals are sent between electronic devices.
Bit, in computer science, short for binary digit; either 1 or 0 in the binary number system (see NUMBER SYSTEMS). In computer processing and storage, a bit is the smallest unit of information handled by a computer and is represented physically by an element such as a single pulse sent through a circuit or a small spot on a magnetic disk capable of storing either a 1 or a 0. Considered singly, bits convey little information a human would consider meaningful. In groups of eight, however, bits become the familiar bytes used to represent all types of information, including the letters of the alphabet and the digits 0 through 9. See also ASCII; BYTE.
Bit-Mapped Font, in computer science, a set of characters in a particular size and style, in which each character is described as a unique bit map (pattern of dots). Macintosh screen fonts are examples of bit mapped fonts.
Bit Mapped Graphics, in computer science, computer graphics that are stored and held as collections of bits in memory locations corresponding to pixels on the screen. Bit mapped graphics are typical of paint programs, which treat images as collections of dots rather than as shapes. Within a computer's memory, a bit mapped graphic is represented as an array (group) of bits that describe the characteristics of the individual pixels making up the image. Bit mapped graphics displayed in colour require several to many bits per pixel, each describing some aspect of the colour of a single spot on the screen. see also vector
Bus (computer), in computer science,
a set of hardware lines—wires—used for data transfer among the components
of a computer system. A bus is essentially a shared highway that connects
different parts of the system—including the microprocessor, disk-drive
controller, memory, and input/output ports—and enables them to transfer
information. Usually supervised by the microprocessor, the bus is, in computers
such as the Apple Macintosh and IBM and compatible models, specialised
for carrying different types of information. One group of wires (actually,
traces on a printed circuit board), for example, carries data; another
carries the addresses (locations) where specific information can be found;
yet another carries control signals to ensure that the different parts
of the system use their shared highway without conflict. Buses are characterised
by the number of bits they can transfer at a single time. A computer with
an 8 bit data bus, for example, transfers 8 bits of data at a time, and
one with a 16 bit data bus transfers 16 bits at a time. Because the bus
is integral to internal data transfer and yet computer users often need
to add extra components to the system, most microcomputer buses allow for
expansion through one or more expansion slots (connectors for add-on circuit
boards). Such boards, when they are added, make an electrical connection
to the bus and effectively become part of the system. see cache
architecture access time bus capacity
cisc computer family computer
co-processor expanded memory hard
drive memory access memory
devices DRAM VRAM EDO RAM
SRAM memory hierarchy
memory organisation microprocessor
pipelining RAM RISC
ROM PROM EPROM EEPROM
Storage storage devices
Cache Is a small amount of fast memory, physically close to the CPU which is used as storage of a block of data regularly accessed by the processor. The smallest and fastest L1 (level 1) cache is incorporated within the processor (since 486) and therefore runs at the speed of the processor. If the processor anticipates the data requirement correctly (90% time) then the systems runs at the speed of the processor. However the 10% of the time that the cache fails to provide the information the processor slows to allow the data to be collected from a slower location which could be main memory. This is classed as a miss and is registered in L2 cache. L2 cache is usually high speed RAM located close to the processor. L2 RAM is still much slower than onboard RAM. Modern processors may include both L1 and L2 cache on the processor. In this case the L1 cache is included within the processor but the L2, whilst onboard the processor chip is external to the actual processor die. This speeds up the access time and L2 cache again has a hit rate in the 90% range. Misses require data to be extracted from slower main memory sources or disk which is far slower. Designed to speed up microprocessor operations. see architecture access time bus capacity cisc computer family computer co-processor expanded memory hard drive memory access memory devices DRAM VRAM EDO RAM SRAM memory hierarchy memory organisation microprocessor pipelining RAM RISC ROM PROM EPROM EEPROM Storage storage devices
CAD (Acronym for Computer-Aided Design, vector based drawing package) the use of computers in creating and editing design drawings. Often allows animation and three dimensional views of the design. Used in architecture, electronics and manufacturing. In the latter case this has been developed further with the use of CAM to integrate with the production line. Used for modelling eg. the amount of wind pressure on an automobile is simulated by computers with Computer-Aided Design (CAD). Colours are used and red may indicates high wind pressures whilst blue indicates low pressures.
2D CAD can be built up in overlays, so a ground floor plan of a house can have a number of overlays showing the power and heating layouts. This allows individual tradesmen to be given a drawing relevant to their area of work eg builders, electricians or plumbers
3D CAD is drawn in a wire form which enables the object to be fully rotated through 360 degrees. Using a FILL facility the object can be given a coloured skin making it appear to be a solid object. Often a CAD package will allow lighting to be simulated. By altering the position of a number of light sources the view of the object can appear more realistic as the programme adjusts shading and applies shadows. This type of programme has been developed further within the film industry to provide cartoon animation scenes. 3D, wire frame models are drawn, then a skin is applied. The skin can be cloned by using a texture contained in another file, eg a file designed to show the texture of the hairs and colouring of a bumble bee can be used as the skin on a 3D model. The bee design can then be replicated, sized and animated. A film scene with actors can be super-imposed with a swarm of bees, totally under the control of the editor.
A Research and Development (R&D) company in the Midlands is developing CAD a stage further to allow prototyping. The dimensions and measurements developed in the CAD design are fed into a further program which controls a machine which uses a laser to cut a resin, three dimensional prototype. The model is then given a fine ceramic coat. Using the lost wax method (a jewellery technique for casting precious metals) the resin is melted and removed leaving a finely detailed ceramic mould which can then be used to cast the object in the desired material (plastic/metal etc). This method, when developed, will remove the need for fully trained tool makers who currently produce the moulds.
CAL (Acronym fore Computer Aided Learning) is the use of computers in education and training. Often the student works alone.
British Telecom used this style of training cutting down on the length of time used to train staff. The training is often broken down into modules. On starting a module students can be asked a few preview questions. If the student shows strong 'prior knowledge' the module is often omitted and the student guided to the next section. A course of three or four week duration could be shortened often to a few days, allowing staff to return to their operational units much earlier. A further development allowed for distance learning, allowing students to study from their home base rather than travel to a residential training college.
CAM (Acronym for Computer Aided Manufacturing) the use of computers to control a production process; the control of machine tools or robots in factories. The design and production process can be automated by linking CAD and CAM. JCB (diggers) and Toyota (Burnaston) use this type of production process.
Capacity, in relation to computers, the amount of information a computer or an attached device can process or store. With respect to specific parts of a computer system, measured in:-
Bit - Byte (8 bits) - kilobytes (1024 bytes) - Megabytes (1024 Kb) - Gigabytes (1024 Mb) - Terabytes
Disk capacity is the total number of bytes (characters) a disk can hold. Because the operating system of a computer requires some space on the disk for its own use, and because files on a disk are stored in blocks rather than byte by byte, disk capacity is greater (although not significantly greater) than available storage space. see floppy disk
Channel capacity is the maximum speed at which a communications channel can transfer data within or between computers.
Memory capacity is, in terms of microcomputers, usually considered the amount of random access memory (RAM) in a computer. Often, however, the term is used to describe the amounts of both RAM and ROM (read-only memory).
Processing capacity refers to the maximum number of operations that a processor can handle in a given unit of time, often expressed in MIPS (millions of operations per second) or FLOPS (floating-point operations per second).
Register capacity is the total number of bits or bytes
that a register in a microprocessor can store.
see cache
architecture access time bus capacity
cisc computer family computer
co-processor expanded memory hard
drive memory access memory
devices DRAM VRAM EDO RAM
SRAM memory hierarchy
memory organisation microprocessor
pipelining
RAM RISC
ROM PROM EPROM
EEPROM Storage storage devices
Complex Instruction Set Computer (CISC) processor A CISC microprocessor contains a more complex set of instructions that it responds to. The complexity of some of these instructions means that the operation cannot be completed in one machine cycle. After an instruction has been decoded on a CISC processor, the actual implementation may require up to 10 or 12 machine cycles dependant upon the instruction and the addressing mode. Some instructions work in the immediate mode where all the information is contained within the instruction; other modes require additional information contained at other locations and machine cycles are required to get this information as well as carry out the instruction. Indexed mode (where a pointer is used point to the required location), indirect mode where part of the instruction indicates the data source and relative mode where the data source is offset from a particular position.
Eg. An ADD IMMEDIATE instruction may just comprise of ADD A IMM, FF where FF is the number to add; this operation can be carried out in a minimum number of machine cycles. However, ADD INDIRECT instruction requires additional cycles as FF would be located at some other address. The instruction may read ADD A IND,09 where the number FF is stored at address 09; this instruction would require extra steps to fetch the number FF from memory location 09 and transfer it to the Register A for the add operation to be carried out.
CISC processors sacrifice speed to be able to accommodate
a wide range of complex instructions and the trend at one time was to go
for even more complex instructions; but in practice only a handful of instructions
are usually used. Because of this processors with a small number of instructions
has been developed. RISC
see cache
architecture access time bus capacity
cisc computer family computer
co-processor expanded memory hard
drive memory access memory
devices DRAM VRAM EDO RAM
SRAM memory hierarchy
memory organisation microprocessor
pipelining
RAM RISC
ROM PROM EPROM
EEPROM Storage storage devices
Computer, 32-Bit Machine, in computer science, a computer that works with information in groups of 32 bits (binary digits) at a time. A description of a computer as a 32-bit machine can either refer to the word size (basic working unit) of its microprocessor or, more commonly, refer to the number of bits transferred along the computer's data bus (data path along which information travels to and from the microprocessor) at a single time. A 32-bit microprocessor thus has a word size of 32 bits, or 4 bytes; a 32-bit data bus has 32 data lines, so it ferries information through the system in sets of 32 bits at a time. The Apple Macintosh II is a 32-bit machine, in terms of both the word size of its microprocessor and the size of the data bus, as are the IBM PS/2 Model 80 and similar models based on the Intel 80386 microprocessor. see cache architecture access time bus capacity cisc computer family computer co-processor expanded memory hard drive memory access memory devices DRAM VRAM EDO RAM SRAM memory hierarchy memory organisation microprocessor pipelining RAM RISC ROM PROM EPROM EEPROM Storage storage devices
Computer Family, in computer science, a term commonly used to indicate a group of computers that are built around the same microprocessor or around a series of related microprocessors and that share significant design features. For example, the Apple Macintosh computers, from the original Macintosh to the Macintosh II, represent a family designed by Apple around the Motorola 68000, 68020, and 68030 microprocessors. Similarly, the IBM PC computers and the "second-generation" PS/2 models can be considered the IBM PC family of computers, all built by IBM around the Intel iAPx86 series of microprocessors. Depending on point of view, however, a computer family can also be considered as encompassing any machines that share the same microprocessor. In this sense, the IBM models and compatible machines built by other manufacturers can be considered part of a larger grouping, the iAPx86 family of computers. Currently, members of different microcomputer families are not particularly compatible (able to use the same operating system and application programs). see cache architecture access time bus capacity cisc computer family computer co-processor expanded memory hard drive memory access memory devices DRAM VRAM EDO RAM SRAM memory hierarchy memory organisation microprocessor pipelining RAM RISC ROM PROM EPROM EEPROM Storage storage devices
Computer, 16-Bit Machine, in computer science, a computer that works with information in groups of 16 bits (binary digits) at a time. A description of a computer as a 16 bit machine can either refer to the word size (basic working unit) of its microprocessor or, more commonly, refer to the number of bits transferred along the computer's data bus (data path along which information travels to and from the microprocessor) at a single time. A 16 bit microprocessor thus has a word size of 16 bits, or 2 bytes; a 16 bit data bus has 16 data lines, so it ferries information through the system in sets of 16 bits at a time. The IBM PC/AT and similar models based on the Intel 80286 microprocessor are 16 bit machines, in terms of both the word size of the microprocessor and the size of the data bus. The Apple Macintosh Plus and Macintosh SE have a 32-bit microprocessor (the Motorola MC68000) but a 16 bit data bus and are generally considered 16 bit machines. see cache architecture access time bus capacity cisc computer family computer co-processor expanded memory hard drive memory access memory devices DRAM VRAM EDO RAM SRAM memory hierarchy memory organisation microprocessor pipelining RAM RISC ROM PROM EPROM EEPROM Storage storage devices
Coprocessor, in computer science, a processor, distinct from the main microprocessor, that performs additional functions or assists the main microprocessor. The most common type of coprocessor is the floating-point coprocessor, also called a numeric or math coprocessor, which is designed to perform numeric calculations faster and better than the general-purpose microprocessors used in personal computers. See see cache architecture access time bus capacity cisc computer family computer co-processor expanded memory hard drive memory access memory devices DRAM VRAM EDO RAM SRAM memory hierarchy memory organisation microprocessor pipelining RAM RISC ROM PROM EPROM EEPROM Storage storage devices
Data Transfer, in computer science, the movement of information from one location to another, either within a computer (as from a disk drive to random access memory) or between a computer and an external device (as between two computers or a file server and a computer on a network). The speed of transfer is called the data rate, or data transfer rate, and is usually measured in bits per second, or bps. The raw data rate (the maximum transfer speed) is usually considerably higher than the actual rate at which meaningful data is transferred because of idle time, error checking procedures, and other overhead. Also, data transfers from different sources to different destinations often compete with each other if they use the same data path—for example, on a network, or on a bus in a computer system.
Digitise, in computer science, to convert any continuously varying source of input, such as the lines in a drawing or a sound signal, into a series of discrete units represented (in a computer) by the binary digits 0 and 1. A drawing or photograph, for example, can be digitised by a scanner that converts lines and shading into combinations of 0's and 1's by sensing different intensities of light and dark. Analogue-to-digital converters are commonly used to perform this translation. See also ALIASING; ANALOG-TO-DIGITAL CONVERTER.
Digital-to-Analogue Converter, or DAC, integrated circuit (IC) for converting digital data into a continuos range of analogue signals. DACs are now widely used in compact disk (CD) players, in digital audio- and videotape players, and in digital signal processing audio and video equipment. Most DACs use some form of resistor network (see RESISTANCE). Digital data is applied to the resistors in groups of bits. The resistances vary in definite ratios; the current flow in each one relates directly to the binary value of the bit received (see COMPUTER). Analogue-to-Digital conversion is the complementary process
Digital Audio Tape (DAT), magnetic tape cassettes used for sound recording and reproduction. Developed for professional use in the 1970 s and for the consumer market by the late 1980 s, digital recorders convert audio signals into digital data on a magnetic tape by means of a microprocessor (an analogue-to-digital converter) and convert the data back into analogue audio signals (by means of a digital-to-analogue converter) for playback with the amplifier of a conventional stereo sound system. In digital recording, sound waves are sampled several thousand times per second and transformed into a series of pulses that correspond to patterns of binary numbers that are recorded on tape (or optical disk).
Digital recorders/players appeared in the early 1980 s in the form of pulse code modulation (PCM) adapters for home videocassette decks. (PCM signalling had been introduced in the UK telephone networks in the early 1960s to reduce congestion on the copper cable distribution network. It acted as a multiplexer by combining 28 individual channels into two pairs of a cable this was later increased to 30 channels and this is the current basis of digital telephony and computer signalling systems) By 1983 the compact disk (CD) developed by the Sony Corporation (Japan) and Philips (the Netherlands), which used a laser beam to read optically pre-recorded digital information on the disk, had brought digital sound into the home market. Digital recordings provide higher fidelity sound reproduction—greater dynamic range and frequency response and less distortion—than conventional analogue methods.
The last obstacle to marketing digital audio tape for home use—the potential to make copies that are indistinguishable from original, copyrighted recordings—was overcome in the late 1980s. Manufacturers adopted the Serial Copy Management System (SCMS), which limits the ability to make digital copies of copies while allowing direct, first generation digital copying of CDs and other digital sources (analogue copying remains unlimited). By mid 1990, home users were able to make CD-quality recordings up to two hours long on durable and reusable cassettes about half the size of standard audio cassettes.
Disk Controller, in computer science, a special purpose chip and associated circuitry that directs and controls reading from and writing to a computer's disk drive. Transferring information to and from a disk drive is a complex operation, and a disk controller handles such tasks as positioning the read/write head, mediating between the drive and the microprocessor, and controlling the transfer of information to and from memory. Disk controllers are used with both floppy disk drives and hard disks. In some computers, the disk controller is built into the system; for example, the floppy disk controller in Macintosh computers is a special chip known as the Integrated Woz Machine (IWM), named in honour of Steven Wozniak, its primary developer. In other machines, such as IBM's original personal computers, the disk controller is on a card that plugs into an expansion slot in the system unit. A single disk controller may be able to control more than one disk drive. See also COMPUTER.
Fibre-Optic Cable Fibre-optic cables provide an alternative to bulky copper wire cables in the telecommunications industry. A single pair of light transmitting optical cables can carry over a thousand conversations simultaneously. Several individual optical cables easily pass through the eye of this needle. David Parker, Science Source/Photo Researchers, Inc.
Expansion Board, in computer science, a circuit board holding chips and other electronic components connected by conductive paths that is plugged into a computer's bus (main data transfer path) to add functions or resources to the computer. Typical expansion boards add memory, disk drive controllers, video support, parallel and serial ports, and internal modems. The simple terms board and card are used interchangeably by most people to refer to all expansion boards. See also COMPUTER; EXPANSION SLOT; PRINTED CIRCUIT BOARD.
Extended Memory, in computer science, system memory beyond
1 megabyte (MB) in computers based on the Intel 80286/386/486 microprocessors.
This memory is accessible only when the processor is operating in protected
mode or in virtual real mode on the 386/486. Extended memory is not typically
available to MS-DOS programs. However, it is available to OS/2 programs
and can be made available to MS-DOS programs by the use of software that
temporarily places the processor into protected mode or by the use of 386/486
features to remap portions of extended memory into conventional memory
based on the EMS conventions. see cache
architecture access time bus capacity
cisc computer family computer
co-processor expanded memory hard
drive memory access memory
devices DRAM VRAM EDO RAM
SRAM memory hierarchy
memory organisation microprocessor
pipelining
RAM RISC
ROM PROM EPROM
EEPROM Storage storage devices
Expanded Memory, in computer
science, on IBM PCs and compatible computers, a type of physical memory,
up to 8 megabytes (MB), that can be added to machines based on the Intel
8086/8088 microprocessor or to machines with 80286/80386/80486 microprocessors
running MS-DOS in real (8086 emulation) mode. The use of expanded memory
is defined by the Expanded Memory Specification (EMS). Because it represents
memory that is not normally accessible to programs running under MS-DOS,
expanded memory requires an interface called the Expanded Memory Manager
(EMM), which maps pages (blocks) of bytes from expanded memory onto reserved
areas called "page frames" in an accessible memory area. Only EMS compatible
software can make use of expanded memory. See also 8086; 8088; 80286; 80386;
80486; see cache architecture
access time bus capacity
cisc computer family computer
co-processor expanded memory hard
drive memory access memory
devices DRAM VRAM EDO RAM
SRAM memory hierarchy
memory organisation microprocessor
pipelining
RAM RISC
ROM PROM EPROM
EEPROM Storage storage devices
Floppy Disk the Personal Computer (PC) was introduced before hard drives were readily available. At the time the standard computer came equiped with two floppy disk drives, one for the system disk and the second personal files or application software disk. In the process of disk management or running an application it was often necessary to change disks a number of times. DOS still includes processes that relate back to those times. All PCs still boot up to look at the A:/ drive before changing to the C:/ drive to find the system files, that is why an error message (non system disk) occurs when a disk of files is inadvertently left in the A:/ drive as a computer boots up. It is also still necessary when setting up a PC for the first time as the computer can refer to the floppy system files and allow the copying of the system files to the C:/ drive on initial set-up (modern computers now have just one floppy drive for this purpose and to allow backing up of files.
Also when running an application, a package it usually remembers the disk that a file has been saved upon, if a disk change has occurred an error message warns the user. This is a remnant from the days when all files were saved upon floppies and care had to be taken that files could be traced. Without checking the current disk in the drive during file saving it would have resulted in files being stored on any disk that happened to be in the drive at the time. This can still happen when saving to floppies, however most people save to their Hard Disk (HD) nowadays.
Early floppy disks came in 8" and 51/4"sizes the latter having typical storage of 360k and 1.2M on the High Density (HD) types. These have been replaced with the 31/2"diskette that most people now refer to as a floppy. This had a more rigid casing, was better protected and the storage platter was more controllable. Because of this higher density of data could be stored on these disks. Typical sizes when introduced was 720K and 1.44M for the HD disk. However at the time of writing the traditional floppy drive is seeing rapid changes in storage capacity. Already 2.88M - 10Mb removable disk storage is available and a number of manufacturers are launching much larger disks.
Caleb (http://www.caleb-bldr.com) have launched an Ultra High Density 144Mb floppy (UHD144) a hundred times the capacity of the present HD disk. They are aiming to develop this further to a 270Mb disk (1999) and 540Mb disk by the millennium (2000). They are aiming at a transfer rate of 970kb /sec better than 7 times the current floppy speeds.
Sony have also launched 200Mb HiFD in two versions, one internal and one external. The transfer rates 3.6Mb/sec but the parallel external version is restricted to 600Kb. ( http://www.sony-cp.com )
Imitation have launched 120Mb SuperDisk ( http://www.imitation.com )
However although all of the drives have been designed to be backwards compatible non are compatible with each other so no industry standard has been set. As in the past, standards will eventually emerge but marketing technique will probably decide the winner rather than technical superiority.
see capacity hard
drive expanded memory RAM
storage devices storage
ROM
Font, traditionally, a set of
characters of the same typeface (such as Courier), style (such as italic),
stroke weight (such as bold), and size. A font is not to be confused with
a typeface. Font refers to all the characters available in a particular
size, style, and weight for a particular design; typeface refers to the
design itself. Fonts are used by computers for on-screen displays and by
printers for hard copy output. In both cases, fonts are created either
from bit maps (patterns of dots) or from outlines (as defined by a set
of mathematical formulas). Programs that allow the use of different fonts
are able to send information about typeface and size to a printer, even
if they are not able to simulate different typefaces on the screen. The
printer can then reproduce the font, provided either that the capability
is built in or that a font description is available to the printer.
Hard Drives were originally the only used in Main-frame computers. Early home computers used a tape drive and didn't necessarily have a dedicated VDU, often using a TV for output. They certainly didn't have a hard drive. With the introduction of the PC a complete work station was designed including a 10Mb hard drive. Currently floppy disk can store more than this. The current version of Windows requires more space than this for installation without the needs of any other application software. Currently an entry level computer would have a disk drive of 4Gb or larger. A laptop computer specification for a hard drive would now be greater than 8Gb.
Hard disks have reduced in size dramatically. An early mainframe disk drive storing 20-30Mb of data would comprise of a number of aluminium platters (12-15" diameter). Modern hard drives for a PC or laptop have a capacity several hundred times greater stored on small aluminium platters 3-3.5" diameter.
Recent releases of hard drives have seen developments
including drives running at 10,000rpm and claiming capacities up to 36Gb
(Fujitsu and Cheetah) and transfer rates up to 66Mb/sec. Manufacturers
using a technology called Giant Magneto-Resistive heads can store 13Gb
and more per platter see floppy
disk Capacity Expanded
memory Storage
Input/Output (I/O), in computer science, two of the three activities (input, processing, and output) that characterise a computer. Input/output refers to the complementary tasks of gathering data for the microprocessor to work with and making the results available to the user through a device such as the display, disk drive, or printer. The keyboard and the mouse are input devices that make information available to the computer; the display and printer are output devices with which the computer makes its results available to the user. A disk drive is both an input and an output device because it can either provide stored information or store the data after processing. See also DATA PROCESSING; DISK DRIVE; KEYBOARD; MOUSE.
Microcomputer, desktop- or notebook size computing device that uses a microprocessor as its central processing unit, or CPU (see COMPUTER). Microcomputers are also called personal computers (PCs), home computers, small business computers, and micros. The smallest, most compact are called laptops. When they first appeared, they were considered single user devices, and they were capable of handling only four, eight, or 16 bits of information at one time. More recently the distinction between microcomputers and large, mainframe computers (as well as the smaller mainframe type systems called minicomputers) has become blurred, as newer microcomputer models have increased the speed and data handling capabilities of their CPUs into the 32-bit, multi-user range.
Microcomputers are designed for use in homes, schools, and office settings. Within the home, they can serve both as a tool for home management (balancing the family chequebook, structuring the family budget, indexing recipes) and as a recreational device (playing computer games, cataloguing records and books). Schoolchildren can use microcomputers for doing their homework, and in fact many public schools now employ the devices for programmed learning and computer literacy courses. Small businesses may purchase microcomputers for word processing, bookkeeping, and the storage and handling of mailing lists.
Integrated Circuit, tiny electronic circuit used to perform a specific electronic function, such as amplification; it is usually combined with other components to form a more complex system. It is formed as a single unit by diffusing impurities into single crystal silicon, which then serves as a semiconductor material, or by etching the silicon by means of electron beams. Several hundred identical integrated circuits (ICs) are made at a time on a thin wafer several centimetres in diameter, and the wafer is subsequently sliced into individual ICs called chips. In large-scale integration (LSI), as many as 5000 circuit elements, such as resistors and transistors, are combined in a square of silicon measuring about 1.3 cm (.5 in) on a side. Hundreds of these integrated circuits can be arrayed on a silicon wafer 8 to 15 cm (3 to 6 in) in diameter. Large-scale integration can produce a silicon chip with millions of circuit elements. Individual circuit elements on a chip are interconnected by thin metal or semiconductor films, which are insulated from the rest of the circuit by thin dielectric layers. Chips are assembled into packages containing external electrical leads to facilitate insertion into printed circuit boards for interconnection with other circuits or components.
During recent years, the functional capability of ICs has steadily increased, and the cost of the functions they perform has steadily decreased. This has produced revolutionary changes in electronic equipment—vastly increased functional capability and reliability combined with great reductions in size, physical complexity, and power consumption. Computer technology, in particular, has benefited greatly. The logic and arithmetic functions of a small computer can now be performed on a single VLSI chip called a microprocessor, and the complete logic, arithmetic, and memory functions of a small computer can be packaged on a single printed circuit board, or even on a single chip. Such a device is called a microcomputer.
In consumer electronics, ICs have made possible the development
of many new products, including personal calculators and computers, digital
watches, and video games. They have also been used to improve or lower
the cost of many existing products, such as appliances, televisions, radios,
and high fidelity equipment. They have been applied in the automotive field
for diagnostics and pollution control, and they are used extensively in
industry, medicine, traffic control (both air and ground), environmental
monitoring, and communications. see cache
architecture access time bus capacity
cisc computer family computer
co-processor expanded memory hard
drive memory access memory
devices DRAM VRAM EDO RAM
SRAM memory hierarchy
memory organisation microprocessor
pipelining
RAM RISC
ROM PROM EPROM
EEPROM Storage storage devices
Memory Access Accessing memory differs according to the type of memory. It is also related to how the memory is organised on a given chip. ROMs come in a variety of formats one bit, four bits or eight bits of data on a given chip and the chips organised into banks/modules to form the required size of memory storage. RAMs also come in a number of forms DRAM access is very different to SRAM in that its row and column address are time multiplexed to reduce the number of pins required on each package. To achieve this DRAM has two address strobe lines RAS and CAS.
Common methods of accessing DRAM include;
Page Mode/Fast Page Mode (FPM), Nibble Mode, static column and Extended Data Output (EDO) mode. see cache architecture access time bus capacity cisc computer family computer co-processor expanded memory hard drive memory access memory devices DRAM VRAM EDO RAM SRAM memory hierarchy memory organisation microprocessor pipelining RAM RISC ROM PROM EPROM EEPROM Storage storage devices
Memory Devices can be categorized according to their function and fall into two major categories read-only-memory (ROM), and read-and-write memory or random-access-memory (RAM). The latter falls into two sub categories which have different storage capabilities; static RAM (SRAM) devices which doers not need refreshing and dynamic RAM (DRAM) which needs periodic refreshing as the contents drain away due to charge leakage. Both SRAM and DRAM are volatile, which means that they loose their charge if the power is removed. All ROM is non volatile.
Except for a few special memories, all devices are interfaced in the same way. When an address is presented to a memory device, the information is stored at a memory location is retrieved after a certain delay time. The process is called memory read and the delay time in making the data ready, is called memory read access time. Data is stored into a memory device by performing a memory write. Control signals also activate the correct memory chip (chip select) other signals may include write control signal. A typical access and write/read process is called the cycle time, which is usually twice the access time.
Some special memory structures do not follow the general accessing scheme of using an address. Content addressable memory (CAM) and first-in-first-out (FIFO) are examples. Another example is video RAM (VRAM), this type of memory can be written in parallel but is read serially. It's primary usage is for graphic display and is used on video cards. see cache architecture access time bus capacity cisc computer family computer co-processor expanded memory hard drive memory access memory devices DRAM VRAM EDO RAM SRAM memory hierarchy memory organisation microprocessor pipelining RAM RISC ROM PROM EPROM EEPROM Storage storage devices
EDO RAM This type of RAM has an additional latch following its sense amplifier. This allows the memory to start pre charging earlier to prepare for the next access and thus speeding up access time. Burst EDO RAM also has additional accessing features allowing even faster data transfer. see cache architecture access time bus capacity cisc computer family computer co-processor expanded memory hard drive memory access memory devices DRAM VRAM EDO RAM SRAM memory hierarchy memory organisation microprocessor pipelining RAM RISC ROM PROM EPROM EEPROM Storage storage devices
Memory Hierarchy Memory speeds have lagged behind processor speeds and in modern computer systems there may be several sub levels of cache memory. A Pentium processor may have on-chip-cache (Level 1). Some processor multi-chip modules also have cache (Level 2). There may also be level-3 cache on the system mother-board, sitting between the CPU chip and the main memory chips (DRAMs) There are also newer memory devices such as synchronous RAM (SRAM) which provides enough speed to be interfaced directly with the processor through pipelining. Cache memory is larger than registers but smaller than main memory.
A general principle of hierarchy is that the further away from the CPU it is, the larger its size, slower its speed, and the cheaper its price per memory unit. Because the memory space addressable by the CPU is normally larger than necessary for a particular software program at a given time, disks are used to provide an economical supplement to main memory. This technique is called virtual memory. Other devices include tape, optical drives and other devices referred as backup storage. These storage devices are mainly used to store information that is no longer in use, to protect against memory and disk failures or to transfer data between machines. see cache architecture access time bus capacity cisc computer family computer co-processor expanded memory hard drive memory access memory devices DRAM VRAM EDO RAM SRAM memory hierarchy memory organisation microprocessor pipelining RAM RISC ROM PROM EPROM EEPROM Storage storage devices
Memory Organisation Memory chips come in a variety of forms. 1 bit, 4 bit, 8 bit etc. Therefore the storage of an 8 bit word could be on a single chip, four bits on one chip/and four bits on another or each individual bit being stored on separate chips. ie in the latter case eight chips would form each bank (9 if parity is catered for) and each word spread across the 8 chips.
On modern computers memory is often formed into modules of varying size. Single-inline-memory-modules (SIMMs) are the most common format. see see cache architecture access time bus capacity cisc computer family computer co-processor expanded memory hard drive memory access memory devices DRAM VRAM EDO RAM SRAM memory hierarchy memory organisation microprocessor pipelining RAM RISC ROM PROM EPROM EEPROM Storage storage devices
Microprocessor, minute, inexpensive central processing unit (CPU) of a small computer, which can also be used independently in a wide range of applications. A microprocessor is built onto a single piece of silicon, called a wafer or chip, that is commonly no longer than 0.5 cm (0.2 in) along one side and no more than 0.05 cm (0.02 in) thick. Despite its small size, a microprocessor may be programmed to perform a great number of information handling tasks. It can serve as a general-purpose computing machine for instructional or word processing use, for controlling other machines or industrial processes, for monitoring hospital patients, and for hand-held calculators. The advent of the microprocessor was made possible by the progressive miniaturisation of integrated circuits and by advances in semiconductor technology. There are two basic forms Complex Instruction Set Computer (CISC) and Reduced Instruction Set Computer (RISC) processors.
A microprocessor may function by itself in a wide range of applications, incorporating as few as 1000 or as many as several hundred thousand elements on its single chip. It may also serve as the CPU of a complete microcomputer, when it is combined with support chips containing computer memories and is equipped with input/output devices. Microcomputers gained great importance in the 1970s and '80s with the growth of the personal and home computers.
A microprocessor chip typically contains a read-only memory (ROM)—that is, a memory that can be read repeatedly but cannot be changed—but it may also have some random-access memory (RAM) for holding transient data. Also present are a register for holding computing instructions, a register for holding the "address" of each instruction in turn, similar data registers, and a logic unit. It also has interfaces for connecting with external memories and other systems as needed.
Microprocessors are classified in terms of the number
of "bits" of information that can be transferred in parallel and held in
their registers. This number has been steadily increasing with the growth
of circuit technology. Thus 4-bit, 8 bit, and 16 bit microprocessors are
now common, and 32-bit chips have also been developed.
High density computer memories, although themselves not
microprocessors, are made by means of the same techniques. By the mid-1980s,
the density commonly attained was about 64,000 bits (64K bits) stored per
individual circuit, but 256 K memories had already appeared and million-bit
units were being developed. Further advances will be determined by theoretical
and practical limits on minimum transistor size.
Methods of executing instructions can be speeded up by
processes such as 2 stage pipelining, cache processors
with such complex operating features (such as the Pentium Pro) are referred
to as super scalar.
see cache
architecture access time bus capacity
cisc computer family computer
co-processor expanded memory hard
drive memory access memory
devices DRAM VRAM EDO RAM
SRAM memory hierarchy
memory organisation microprocessor
pipelining
RAM RISC
ROM PROM EPROM
EEPROM Storage storage devices
Modem, device that converts between analogue and digital signals. Digital signals, which are used by computers, are made up of separate units, usually represented by a series of 1's and 0's. Analogue signals vary continuously; an example of an analogue signal is a sound wave. Modems are often used to enable computers to communicate with each other across telephone lines. A modem converts the digital signals of the sending computer to analogue signals that can be transmitted through telephone lines. When the signal reaches its destination, another modem reconstructs the original digital signal, which is processed by the receiving computer. If both modems can transmit data to each other simultaneously, the modems are operating in full duplex mode; if only one modem can transmit at a time, the modems are operating in half duplex mode.
To convert a digital signal to an analogue one, the modem generates a carrier wave and modulates it according to the digital signal. The kind of modulation used depends on the application and the speed of operation for which the modem is designed. For example, many high speed modems use a combination of amplitude modulation, where the amplitude of the carrier wave is changed to encode the digital information, and phase modulation, where the phase of the carrier wave is changed to encode the digital information. The process of receiving the analogue signal and converting it back to a digital signal is called demodulation. The word "modem" is a contraction of its two basic functions: modulation and demodulation.
Multiplexing, in computer science,
a technique used in communications and input/output operations for transmitting
a number of separate signals simultaneously over a single channel or line.
To maintain the integrity of each signal on the channel, multiplexing can
separate the signals by time, space, or frequency. The device used to combine
the signals is a multiplexer.
Origins
Microcomputers were made possible by two technical innovations
in the field of microelectronics: the integrated circuit, or IC, which
was developed in 1959; and the microprocessor, which first appeared in
1971. The IC permitted the miniaturization of computer memory circuits,
and the microprocessor reduced the size of a computer's CPU to the size
of a single silicon chip.
Because a CPU calculates, performs logical operations,
contains operating instructions, and manages data flows, the potential
existed for developing a separate system that could function as a complete
microcomputer. The first such desktop size system specifically designed
for personal use appeared in 1974; it was offered by Micro Instrumentation
Telemetry Systems (MITS). The owners of the system were then encouraged
by the editor of a popular technology magazine to create and sell a mail-order
computer kit through the magazine. The computer, which was called Altair,
retailed for slightly less than $400.
The demand for the microcomputer kit was immediate, unexpected,
and totally overwhelming. Scores of small entrepreneurial companies responded
to this demand by producing computers for the new market. The first major
electronics firm to manufacture and sell personal computers, Tandy Corporation
(Radio Shack), introduced its model in 1977. It quickly dominated the field,
because of the combination of two attractive features: a keyboard and a
cathode-ray display terminal (CRT). It was also popular because it could
be programmed and the user was able to store information by means of cassette
tape.
Soon after Tandy's new model was introduced, two engineer-programmers—Stephen
Wozniak and Steven Jobs—started a new computer manufacturing company named
Apple Computers. Some of the new features they introduced into their own
microcomputers were expanded memory, inexpensive disk drive programs and
data storage, and colour graphics. Apple Computers went on to become the
fastest growing company in U.S. business history. Its rapid growth inspired
a large number of similar microcomputer manufacturers to enter the field.
Before the end of the decade, the market for personal computers had become
clearly defined.
In 1981, IBM introduced its own microcomputer model, the IBM PC. Although it did not make use of the most recent computer technology, the PC was a milestone in this burgeoning field. It proved that the microcomputer industry was more than a current fad, and that the microcomputer was in fact a necessary tool for the business community. The PC's use of a 16 bit microprocessor initiated the development of faster and more powerful micros, and its use of an operating system that was available to all other computer makers led to a de facto standardization of the industry.
Later Developments
In the mid-1980s, a number of other developments were
especially important for the growth of microcomputers. One of these was
the introduction of a powerful 32-bit computer capable of running advanced
multi-user operating systems at high speeds. This has dulled the distinction
between microcomputers and minicomputers, placing enough computing power
on an office desktop to serve all small businesses and most medium size
businesses.
Another innovation was the introduction of simpler, "user-friendly"
methods for controlling the operations of microcomputers. By substituting
a graphical user interface (GUI) for the conventional operating system,
computers such as the Apple Macintosh allow the user to select icons—graphic
symbols of computer functions—from a display screen instead of requiring
typed commands. New voice controlled systems are now available, and users
may eventually be able to use the words and syntax of spoken language to
operate their microcomputers.
Contributed by:
Gary Masters
Peripheral, in computer science, a term used for devices, such as disk drives, printers, modems, and joysticks, that are connected to a computer and are controlled by its microprocessor. Although peripheral often implies "additional but not essential," many peripheral devices are critical elements of a fully functioning and useful computer system. Few people, for example, would argue that disk drives are nonessential, although computers can function without them. Keyboards, monitors, and mice are also strictly considered peripheral devices, but because they represent primary sources of input and output in most computer systems, they can be considered more as extensions of the system unit than as peripherals. See also DISK DRIVE; INPUT/OUTPUT DEVICE; JOYSTICK; KEYBOARD; MODEM; MOUSE.
Pipelining is a microprocessor architecture technique that divides the execution of an instruction into sequential steps. Pipelined CPUs have multiple instructions executing at the same time but at different stages in the machine. Or, the act of sending out an address before the data is actually needed. Some processors have inbuilt supervisor and and user modes and can fetch the next instruction whilst another instruction is being executed. (this represents 2 stage pipelining)
A typical Microsystems MC68060 processor around 1995 was
a super scalar processor similar to the Intel Pentium and
has
complicated 10-stage pipelining.
see cache
architecture access time bus capacity
cisc computer family computer
co-processor expanded memory hard
drive memory access memory
devices DRAM VRAM EDO RAM
SRAM memory hierarchy
memory organisation microprocessor pipelining
RAM RISC ROM PROM EPROM
EEPROM Storage storage devices
Pixel, in computer science, short for picture element; sometimes called a pel. One spot in a rectilinear grid of thousands of such spots that are individually "painted" to form an image produced on the screen by a computer or on paper by a printer. Just as a bit is the smallest unit of information a computer can process, a pixel is the smallest element that display or print hardware and software can manipulate in creating letters, numbers, or graphics. For example, the letter A is actually made up of a pattern of pixels in a grid .
PixelA pixel (short for "picture element") is one of thousands of tiny spots in a grid on a display screen or printed sheet. These spots, or blocks, are individually coloured in order to show images on computer screens, and represent the smallest elements that may be manipulated to create graphics. Because they are not infinitely small, pixels only approximate the actual colouring of a subject. For this reason, computer generated images (called bit maps or pixel maps) often look slightly jagged, or "blocky," under close examination.
An image can also be represented in more than two colors—for
example, in a range of grays:
If a pixel has only two colour values (typically black
and white), it can be encoded by 1 bit of information. If more than 2 bits
are used to represent a pixel, a larger range of colours or shades of gray
can be represented: 2 bits for four colours or shades of gray, 4 bits for
sixteen colours, and so on. Typically, an image of two colours is called
a bit map, and an image of more than two colours is called a pixel map.
See also Bit mapped graphics
Port, in computer hardware,
a location for passing data in and out of a computing device. Microprocessors
have ports for sending and receiving data bits; these ports are usually
dedicated locations in memory. Full computer systems have ports for connecting
peripheral devices such as printers and modems.
In programming, to change a program in order to run it
on a different computer; more loosely, to move documents, graphics, and
other files from one computer to another.
RAM, in computer science, acronym for random access memory. Semiconductor based memory that can be read and written by the microprocessor or other hardware devices. The storage locations can be accessed in any order. Note that the various types of ROM memory are capable of random access. The term RAM, however, is generally understood to refer to volatile memory, which can be written as well as read. Originally only 512Kb of RAM was accessible later extended to 640K. With the rapid development of application software and Graphical User Interfaces (GUI) to make computing more user-friendly larger amounts of RAM was required for use during run-time. The ability to open several windows simultaneously, each with possibly a different application software package opened, or with several web pages when using the Internet has resulted in minimum computer RAM specification of 32MB, 64Mb, 128Mb and even larger.
RAM can be categorized by by content duration. A static RAMs contents will be retained as long as power is applied. However, DRAM needs to be refreshed every few milliseconds. ROM is non volatile but RAM looses its memory when power is switched off. However, RAM can be made non volatile by providing a backup battery.
Varieties of RAM include SRAM, DRAM
and VRAM.
see cache
architecture access time bus capacity
cisc computer family computer
co-processor expanded memory hard
drive memory access memory
devices DRAM VRAM EDO RAM
SRAM memory hierarchy
memory organisation microprocessor
pipelining
RAM RISC
ROM PROM EPROM
EEPROM Storage storage devices
Reduced Instruction Set Computing (RISC), in computer science, a type of microprocessor design that focuses on rapid and efficient processing of a relatively small set of instructions. RISC design is based on the premise that most of the instructions a computer decodes and executes are simple. As a result, RISC architecture limits the number of instructions that are built into the microprocessor but optimizes each so it can be carried out very rapidly—usually within a single clock cycle. RISC chips thus execute simple instructions faster than microprocessors designed to handle a much wider array of instructions. Families of RISC chips that are gaining popularity include Sun Microsystems' SPARC, Motorola's PowerPC, Digital Equipment Corporation's Alpha, and MIPS R4000 and R4400.
RISC processors have few instructions and few machine cycles to implement them but they use a lot of registers and parallelism. In fact both RISC and CISC philosophies have merits and future systems may find it advantageous to combine the two philosophies. Early RISC processors included MIPS R2000, Hewlett Packard PA-RISC and the AMD 29000. The latter uses a large number of registers split into local and global sets. CISC processors usually only have a few registers. see cache architecture access time bus capacity cisc computer family computer co-processor expanded memory hard drive memory access memory devices DRAM VRAM EDO RAM SRAM memory hierarchy memory organisation microprocessor pipelining RAM RISC ROM PROM EPROM EEPROM Storage storage devices
ROM, acronym for read-only memory. In computer science, semiconductor based memory that contains instructions or data that can be read but not modified. To create a ROM chip, the designer supplies a semiconductor manufacturer with the instructions or data to be stored; the manufacturer then produces one or more chips containing those instructions or data. Because creating ROM chips involves a manufacturing process, it is economically viable only if the ROM chips are produced in large quantities; experimental designs or small volumes are best handled using PROM or EPROM. In general usage, the term ROM often means any read-only device, including PROM and EPROM.
In many systems, it is desirable to have the system level software (eg. basic input/output system BIOS) stored in a read-only format, because the programs are seldom changed. I general, information stored in ROM is permanent, it is retained even when the power is turned off. The information can be read out reliably by simple current sensing circuits, without destroying the stored data.
Masked ROM, normally referred to as just ROM, is the most basic type; Programmed at time of manufacture. The process is performed at the factory. see cache architecture access time bus capacity cisc computer family computer co-processor expanded memory hard drive memory access memory devices DRAM VRAM EDO RAM SRAM memory hierarchy memory organisation microprocessor pipelining RAM RISC ROM PROM EPROM EEPROM Storage storage devices
Programmable ROM (PROM) Some ROM is one time programmable and can be programmed by the user on site. It uses bi-polar technology. Each transistor in a cell has a fusable link connected to it's emitter. Once the fuse has been blown it cannot be reset. A blown fuse represents a zero and an intact link represents a logic one. PROM programmer or PROM burner equipment is required for this operation. see cache architecture access time bus capacity cisc computer family computer co-processor expanded memory hard drive memory access memory devices DRAM VRAM EDO RAM SRAM memory hierarchy memory organisation microprocessor pipelining RAM RISC ROM PROM EPROM EEPROM Storage storage devices
Erasable programmable ROM (EPROM) It is sometimes inconvenient to to programme the ROM only once. (eg British Telecom stored current tarrif/call charging information in ROM, but periodically the tariffs would be changed and the ROMs would require re-programming). EPROMs were suitable devices for this.
The programming of a cell is performed applying a high drain voltage, this causes electrons to jump between the substrate and the silicon dioxide (which forms a gate), collecting a charge at the floating gate. Once the applied voltage is removed the charge is trapped on the floating gate. UV light causes the trapped voltages to be released. This type of chip usually has a small circular window covered by a light proof label. Removing this label and placing the ROM in a device containing a high density UV light source (sometimes referred to as an oven) causes the ROM to be reset, in readiness for re-programming. All addresses have to be reprogrammed, it is not possible to select individual memory locations. see cache architecture access time bus capacity cisc computer family computer co-processor expanded memory hard drive memory access memory devices DRAM VRAM EDO RAM SRAM memory hierarchy memory organisation microprocessor pipelining RAM RISC ROM PROM EPROM EEPROM Storage storage devices
Electrical Erasable ROM (EEPROM) It is inconvenient to have to remove a chip to prepare it for programming using a separate light source. EEPROMs allow the erasing of data to be achieved with the ROM in situ. The main difference between EPROMs and EEPROMs is the way that they discharge the charge stored in the floating gate. Fowler-Nordheim tunnelling technique (allowing low energy electrons to jump the gap) this alows the gate to be discharged when required. It is possible to change just individual locations.
Flash EEPROM is a more
recent introduction and works in a similar fashion to EEPROM but requires
all addresses to be reprogrammed, not just single addresses.
See also see cache
architecture access time bus capacity
cisc computer family computer
co-processor expanded memory hard
drive memory access memory
devices DRAM VRAM EDO RAM
SRAM memory hierarchy
memory organisation microprocessor pipelining
RAM RISC ROM PROM EPROM
EEPROM Storage storage devices
Smart Terminal, in computer science, a terminal that contains a microprocessor and random access memory (RAM) and that does some rudimentary processing without intervention from the host computer. Generally, a smart terminal can limit keyboard input to particular fields of the display and can perform some input validation (such as restricting input to numbers). See also COMPUTER; DUMB TERMINAL; INTELLIGENT TERMINAL; LAN; TELECOMMUNICATIONS.
Storage, in relation to computers, any physical device in or on which computer information can be kept. A microcomputer has two main types of storage. Its random access memory (RAM) represents temporary storage that the microprocessor uses for programs, work in progress, and various types of internal work control information. The computer's disk drives and other external storage media represent facilities for holding information on a more permanent basis, available but out of the way until it is needed by the microprocessor. A computer has other types of storage as well. Its read-only memory (ROM) is a permanent, non erasable medium for holding necessary information, including start-up instructions and input/output procedures. In addition, a computer uses various buffers—reserved areas of memory—as temporary holding areas designated for specific information, such as characters to be sent to the printer or characters being read from the keyboard. See also see cache architecture access time bus capacity cisc computer family computer co-processor expanded memory hard drive memory access memory devices DRAM VRAM EDO RAM SRAM memory hierarchy memory organisation microprocessor pipelining RAM RISC ROM PROM EPROM EEPROM Storage storage devices
Storage Device, in computer
science, any apparatus for recording computer data in permanent or semi-permanent
form. A disk drive, along with the disks it records on, is a storage device.
Sometimes a computer is said to have primary (or main)
and secondary (or auxiliary) storage devices. When this distinction is
made, the primary storage device is the computer's random access memory
(RAM)—impermanent, but a storage device nevertheless, however temporary
its contents. The secondary storage includes the computer's more permanent
storage devices, such as disk and tape drives. See see cache
architecture access time bus capacity
cisc computer family computer
co-processor expanded memory hard
drive memory access memory
devices DRAM VRAM EDO RAM
SRAM memory hierarchy
memory organisation microprocessor pipelining
RAM RISC ROM PROM EPROM
EEPROM Storage storage devices
Vector Graphics, in computer
science, a method of generating images that uses mathematical descriptions
to determine the position, length, and direction in which lines are to
be drawn. In vector graphics, objects are created as collections of lines,
rather than as patterns of individual dots (pixels), as is the case with
raster graphics. See bitmap
|
|
|
|
