Pronounced ''Cash". A special area of memory, managed by a cache controller, that improves performance by storing the contents of frequently accessed memory locations and their addresses. When the processor references a memory address, the cache checks to see if it holds that address. If it does, the information is passed directly to the processor; if not, a normal memory access takes place instead. A cache can speed up operations in a computer whose RAM access is slow compared with its processor speed, because the cache memory is always faster than normal RAM.
There are several types of cache architecture:
Direct-mapped cache: A location in the cache corresponds to several specific locations in memory, so when the processor calls for certain data, the cache can locate it quickly. However, since a several blocks in RAM correspond to the same location in the cache, the cache may spend its time refreshing itself and calling main memory.
Fully associative cache: Information from RAM may be placed in any free blocks in the cache, so that the most recently accessed data is usually present; however, the search to find that information may be slow because the cache has to index the data to find it.
Set-associative cache: Information from RAM is kept in sets, and these sets may have multiple locations, each holding a block of data; each block may be in any of the sets, but it will only be in one location within that set. Search time is shortened, and it is less likely that frequently-used data will be overwritten. A set-associative cache may use two, four or eight sets.
Memory cache: An area of high-speed memory on the processor that stores commonly used code or data obtained from slower memory, replacing the need to access the system's main memory to fetch instructions.
Disk cache: An area of computer memory where data is temporarily stored on its way
to or from a disk.
A disk cache mediates between the application and the hard disk and improves hard disk performance.
Caps Lock key
A toggle key on the keyboard that shifts the alphabetical characters on the key
board into uppercase when it is on. The Caps Lock key does not change the case of
the numbers or punctuation keys on the keyboard; you must use the Shift key for this.
A printed circuit board or adaptor that you plug into your computer to add support for a specific piece of hardware not normally present on the computer.
An extension of the main computer bus that includes expansion slots for use by compatible adaptors, such as including memory boards, video adaptors, hard disk controllers, and SCSI interface cards.
Aterm describing add-on cards that conform to the PCMCIA (Personal Computer Memory Card International Association) standard.
Abbreviation for PC Memory Card International Association. The majority of PCMCIA devices are modems, Ethernet and Token Ring network adaptors, dynamic RAM, flash memory cards, mini-hard disks, wireless LAN adaptors, and SCSI adaptors etc.
Abbreviation for personal digital assistant. A tiny pen based palmtop computer that combines fax, e-mail, PCMCIA support, and simple word processing into an easy-to-use unit that fits into a pocket. PDAs are available form several manufacturers.
Part of the software support needed for PCMCIA hardware devices in a portable computer, controlling the use of system interrupts, memory, or power management.
When an application wants to access a PC Card, it always goes through the card services software and never communicates directly with the underlying hardware.
In a windowed environment, the arrangement of several overlapping windows so that their title bars are always visible. The windows appear to be stacked, one behind the other.
In a graphical user interface, a menu selection that leads to one or more further menus; usually indicated by a right-pointing triangle.
If you choose one of these commands, the cascading menu opens to the right of the original menu, and you make your selection from this menu just as you wouldfrom any menu. Cascading menus are often used to reduce the number of entries in a main menu.
Abbreviation for CD Recordable. A type of CD device that brings CD-ROM publishing into the realm of the small business or home office. From a functional point of view, a CD-R and a CD-ROM are identical; you can read CD-R discs using almost any CD-ROM drive, although the processes that create the discs are slightly different.
Acronym for Compact Disc-Read Only Memory, pronounced "see-dee-rom". A high-capacity, optical storage device that uses compact disc technology to store large amounts of information up to 650 MB.
CD-ROMs are important components of multimedia PCs, and are used to store encyclopedias, dictionaries and other large reference works, libraries of fonts and clip art for desktop publishing, and are increasingly used as the distribution mechanism for large software packages.
CD-ROMs are usually considered to be WORM (write once, read many) devices, but several vendors (including Kodak) are working toward a format that will allow home users to add information to an existing multisession compact disk.
A set of non-copyrighted or public domain graphical images, photographs, maps, or line art, usually on disk, that you can import into a word processor, desktop publishing program, or presentation graphics program and incorporate into other documents.
You can then resize, rotate, or edit the image to your satisfaction.
An area of memory reserved for temporary storage of text or graphics being transferred within the same file, between files in the same application program, or between applications. Material placed on the clipboard remains there until it is replaced by another selection, or the computer is turned off or restarted.
An electronic circuit that generates regularly-spaced timing pulses at speeds of upto millions of cycles per second.
These pulses are used to synchronise the flow of information through the computer's internal communications channels.
An internal time-of-day and month-year calendar that is kept up-to-date by a small battery-backup system. This allows your computer to update the time even when turned off. Appointment scheduling programs and programs that start at specific times use the output from the clock/calendar board.
Also known as clock rate. The internal speed of a computer or processor, normallyexpressed in MHz.
The faster the clock speed, the faster the computer will perform a specific operation, assuming the other components in the system, such as disk drives, can keep up with the increased speed.
The smallest unit of harddisk space that DOS can allocate to a file, consisting of one or more contiguous sectors.
The number of sectors contained in a cluster depends on the hard disk type.
An unexpected program halt, sometimes due to a hardware failure, but most often due to a software error, from which there is no recovery. You will probably have to reboot your computer to recover after a crash.
The extent to which a given piece of hardware or software conforms to an accepted standard, regardless of the original manufacturer. In hardware, compatibility is often expressed in terms of certain other widely accepted models, such as a computer described as IBM-Compatible, or a modem as Hayes-compatible. This implies that the device will perform in every way just like the standard device.
In software, compatibility is usually described as the ability to read data file formats created by other vendors' software, or the ability to work together and share data.
A version of the BASIC programming language that allows you to compile the program, rather than run the BASIC interpreter.
Compiled programs generally tend to execute faster than interpreted programs, which translate and execute instructions line-by-line through the program.
A file that has been processed by a special utility program so that it occupies as little hard-disk space as possible. When the file is needed, the same program decompresses the file back into its original form so that it can be read by the computer.
Abbreviated CAD; the use of a computer and specialised CAD software in the design of a product. Specialised CAD systems are used to design buildings and landscapes, aircraft, mechanical parts, or printed circuit boards.
CAD reduces the time needed to create, edit, store, and transmit drawings byusing high-performance computers and monitors, with input devices like scanners and graphics tablets.
Computer-aided software engineering
Abbreviated CASE. Development software that is used to aid all aspects of the software life cycle, including the design, coding, testing, documenting, and maintenance of software.
CASE provides a set of programming and development tools that help programmers
to automate the production of business, technical, and engineering software.
Abbreviated CIM. The integration of automated factory systems with office and accounting functions. Sales, billing, work order creation, machine tool scheduling inventory control, and purchasing all access a common database that is used throughout
all aspects of the manufacturing process by all departments.
Some advanced CIM systems also include CAD functions and robotic assembly lines.
In Microsoft Windows, the menu that appears when you click on the Controlmenu box at the top left corner of any application window, or when you click on any application icon.
The control menu lists options you can use to change the overall size and shape of the active window, as well as close the current window or switch to another application window.
In the Macintosh and in Microsoft Windows, a selection that contains setting to control hardware options such as the mouse, display, and keyboard.
On the Macintosh, the Control Panel is a desk accessory, while in Windows, it is a program contained in the Main group window.
To duplicate part of a document and reproduce it elsewhere. The material copied can range from a single character to pages of text and graphics. A copy operation leaves the original in place and unchanged.
In desktop publishing, small intersecting lines at the corners of the page used if the final page size will be smaller than the paper size. The crop marks show where the paper should be cut down to the desired size.
A special character on a display screen to indicate where the next character willappear when it is typed. In text or character mode, the cursor is usually a blinking rectangle or underline. In a graphical user interface, the cursor can take many shapes, depending on the current operation, and may also change shape as it moves to different parts of the screen.
The keys on the keyboard that move the cursor, including the four keys labelled with arrows, as well as the Home, PgUp, End, and PgDn keys.
ADOS and OS/2 command used in the start-up configuration file, CONFIG.SYS, to load a specific device driver into memory. For example, DOS does not contain software to manage a mouse, so before you can use one on your system, you must first load the appropriate device driver.
A small program that allows a computer to communicate with and control a device.
Each operating system contains a standard set of device drivers for the keyboard, the monitor, and so on, but if you add specialised peripherals such as a CD-ROM disk drive, or a network interface card, you will probably have to add the appropriate device driver so that the operating system knows how to manage the device.
The name used by the operating system to identify a computer-system component.
For example, LPT 1 is the DOS device name for the first parallel part.
A program that tests computer hardware and peripherals for correct operation. In the PC, some faults are easy to find, and these are known as "hard faults"; the diagnostic program will diagnose them correctly every time. Others, such as memory faults, can be difficult to find; these are called "soft faults" because they do not occur every time the memory location is tested, but only under very specific circumstances.
Pronounced "dry-stone". Astandard general-purpose benchmark program used to quantify and compare the performance of different computers. The program reports system performance as the number of times that the program can operate per second. This benchmark program concentrates on string and general-purpose instructions.