A file that ordinarily is not visible in the file directory and cannot be accessed by unauthorized users. Some operating system files are hidden, to prevent inexperienced users from inadvertently deleting or changing these essential files. Some file utility programs also allow users to hide files. In DOS and DOS-related operating systems, the dir command lists all files except hidden files. In versions of DOS since 5.0, the command dir /ah will list hidden files. In UNIX, the ls command lists all files except hidden files (files whose names begin with a dot); the command ls -al lists the hidden files.
Extensible Markup Language. A programming language developed by the World Wide Web Consortium; essentially a simplified version of SGML that allows Web developers to create customized tags that will organize and deliver content with more efficiently. XML is a metalanguage, containing a set of rules for constructing other markup languages. By allowing people to make up their own tags, it expands the amount and kinds of information that can be provided about the data held in documents. Some of the advantages are: search engines will be able to zoom in on one particular meaning of a word; new languages can be employed that will allow musical notation and mathematical and chemical symbols to be used as easily as text; e-commerce will become more practical. The World Wide Web Consortium published XML 1.0 in December 1997 www.w3c.org/XML/). Microsoft is a huge proponent of XML, often claiming it will replace HTML and become the next industry standard.
A program which displays a table of numbers in rows and columns, used for accounting, budgeting, financial analysis, scientific applications, and other work with figures. Originally, paper spreadsheets were used; the computerized versions have the advantage of being able to perform automatic calculations on changing data. Each location in a spreadsheet is called a cell, and each cell has a number, such as A3, B4, etc. The value of a cell may be calculated from a formula involving other cells; for example, C5 may be the sum of A5 and B5. If the data entered in A5 changes, then C5 would be automatically recalculated by the program. This feature makes it possible to use a spreadsheet to project the results of a change in one or more factors. References between cells may be designated as absolute or relative; an absolute reference refers to a specific cell, and a relative reference describes a cell in its relation to the current cell (as two rows above, two columns to the left, etc.). The data within a cell may be a label, a number, or a formula, and may be copied to other cells. There are two- and three-dimensional spreadsheets. The first commercially available spreadsheet program was VisiCalc for Apple II; now there are spreadsheet programs from Microsoft, Borland, Lotus, and many other companies. Microsoft Excel and Lotus 1-2-3 are popular examples.
Sockets on a computer that are usually used to connect a modem, mouse, scanner, or serial printer. Sometimes two computers are connected together by their serial ports to send data between them. A serial port, also called a male connector, has 9 or 25 pins. A serial port sends information through a cable one bit at a time, whereas a parallel port sends eight bits at a time along parallel wires. A parallel port sends data faster but a serial port is reliable for transmission over a longer distance.
Peripheral Component Interconnect bus. A personal computer local bus designed by Intel, which runs at 33 MHz and supports Plug and Play. It provides a high-speed connection with peripherals and allows connection of seven peripheral devices. It is mostly used with Pentium computers but is processor independent and therefore able to work with other processors. It plugs into a PCI slot on the motherboard and can be used along with an ISA or EISA bus.
|video graphic cards|
Accelerator cards that enhance 3D graphics, 2D graphics, videoconferencing, and multimedia. A videographic accelerator card can assist in delivering powerful and high-resolution throughput by performing much of the graphics processing that would otherwise be done by the CPU.
|virtual device driver|
(VxD). A virtual device driver is the component of a device driver that communicates directly between an application and a hardware device. Virtual device drivers organize the flow of data to allow more than one application to access the same hardware without conflict. In the device file name, V stands for virtual and D stands for device. The "x" can be replaced with other characters; for example, VmD means a mouse driver.
(phtml). Some HTML documents have embedded equations or other material not expressible in HTML. To embed the non-HTML data, preprocessing instructions (PPIs) are used. Using a program called phtml, the document is then translated into a new HTML document with the equations included as inline pictures. These HTML documents with PPIs have the file extension .PHTML.
- A part of a network, which has the same network address as other parts of the network but a unique subnet number; a subdivisional network interconnected and situated within a larger network. 2. Within the ISO/OSI reference model, the layers below the transport layer are referred to as the subnet. They consist of the network, data link, and physical layers.
|OnLine Analytical Processing|
(OLAP). A method of database indexing that enhances quick access to data, especially in queries calling for large quantities of data or viewing the data from many different aspects.
A "mainframe" originally meant the cabinet containing the central processor unit of a very large computer. After minicomputers became available, the word mainframe came to refer to the large computer itself. The older computers used many large vacuum tubes and generated a lot of heat, thus requiring specially air-conditioned rooms. A single computer might have hundreds of users at a time. Today, because the large vacuum tubes have given way to transistors, a desktop personal computer can have as much power as a mainframe computer that once filled a whole room. Mainframe computers in use now often have smaller computers as front end processors.
Synchronous Dynamic Random Access Memory (SDRAM). High-speed DRAM that adds a separate clock signal to the control signals. SDRAM can transfer bursts of non-contiguous data at 100 MBytes/sec, and has an access time of 8-12 nanoseconds. It comes in 64-bit modules: long 168-pin DIMMs.
Open DataBase Connectivity. An interface that makes it possible to access different database systems with a common language. ODBC is based on CLI (Call Level Interface); there are ODBC drivers and development tools for Windows, Macintosh, UNIX, and OS/2.
The unique name that identifies a computer on a network. On the Internet, the host name is in the form "comp.xyz.net"; if there is only one Internet site the host name is the same as the domain name. One computer can have more than one host name if it hosts more than one Internet site, however (for example, "home.xyz.net" and "comp.xyz.net"); in that case "comp" and "home" are host names and "xyz.net" is the domain name.
|OLE custom control|
(OCX). A special-purpose program module that can be used by applications in a Windows environment. Examples of functions handled by OCX are scroll bars and the ability to resize windows. OCX controls superseded VBX controls, which were written in Visual Basic. OCX controls have been superseded by ActiveX controls; however, ActiveX is backward compatible with OCX. OCX control files end with the .OCX extension.
(OO). Having to do with or making use of objects; an object in this sense is a component containing both data and instructions for the operations to be performed on that data. In object-oriented programming, these reusable components are linked together in various ways to create applications.
A device that uses light to read patterns, and may then convert the patterns into digital or analog signals. An optical scanner used as an input device for a computer can scan a picture or page of text and convert it into digital code as a graphics or text file on the computer. There are flatbed scanners which look like photocopiers, having a glass scanning surface to put the original on; sheetfed scanners in which the original is guided across the scanner; and handheld scanners which the user has to move across the area being scanned. See also bar code scanner, optical reader, optical character recognition.
Stuffing a web page full of words in the hope of making it high on the list for search engine robots. Sometimes a web page will have a list of many words, or the same word repeated many times, with the text in the same color as the background. Spamdexing will cause a web page to be kicked from search engine indexes.
A variety of methods that can be used to correct the keystoning effect often seen on overhead and front room projectors. For example, the angle of the screen can be adjusted. There are optical methods of keystone correction; some projectors apply a reverse keystone to the image, which cancels out the normal keystoning effect. Keystoning is less of a problem with mid-room projectors that can be located farther away from the screen. There are also digital methods of keystone correction, for example, in Photoshop 4.0.
(OS). An operating system is the main control program of a computer that schedules tasks, manages storage, and handles communication with peripherals. An operating system presents a basic user interface when no applications are open, and all applications must communicate with the operating system. Some computers can switch between operating systems (see dual boot) or run another operating system under emulation. Examples of operating systems are Windows, DOS, MacOS, Linux, UNIX, OS/2, RISC OS, etc.
Preparing a disk so a computer can read and write data on it. Formatting a disk includes creating the physical tracks and sector identification, and creating the indexes specific to the operating system it will be used on. Floppy disks can be bought preformatted or can be formatted by the user with a program on the computer.
Software from Microsoft DirectX that improves 3D graphics in games; 3-D graphics programming interface from Microsoft for Windows 95 and NT that provides low-level access to the frame buffer and advanced features of the display adapter for the creation of high-speed animation.
Also called Bezier spline. A curve made of a line that is set up to connect two points, but has two other points that influence the shape of the line by "pulling" it toward them into a curve. In computer drawing programs, curves are made by moving onscreen "handles" to adjust the curve's shape, thus creating a Bezier curve. Bezier curves are named after Pierre Bezier, who discovered the mathematical formula.
One of the gateways operated by the Internet Network Operations Center at Bolt, Beranek and Newman (BBN). The core gateway system originally formed a central part of Internet routing; all groups had to advertise the paths to their networks from one of the core gateways.
Same as public-key cryptography. A form of cryptography in which each user has a public key and a private key. Messages are sent encrypted with the receiver's public key; the receiver decrypts them using the private key. Using this method, the private key never has to be revealed to anyone other than the user.