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Definitions of Terms A utility that searches a hard disk for viruses and removes any that are found. Most antivirus programs include an auto-update feature that enables the program to download profiles of new viruses so that it can check for the new viruses as soon as they are discovered. The precursor to the Internet, ARPANET was a large wide-area network created by the United States Defense Advanced Research Project Agency (ARPA). Established in 1969, ARPANET served as a testbed for new networking technologies, linking many universities and research centers. The first two nodes that formed the ARPANET were UCLA and the Stanford Research Institute, followed shortly thereafter by the University of Utah. Also Known As the MBR Short for Master Boot Record, a small program that is executed when a computer boots up. Typically, the MBR resides on the first sector of the hard disk. The program begins the boot process by looking up the partition table to determine which partition to use for booting. It then transfers program control to the boot sector of that partition, which continues the boot process. In DOS and Windows systems, you can create the MBR with the FDISK /MBR command. An MBR virus is a common type of virus that replaces the MBR with its own code. Since the MBR executes every time a computer is started, this type of virus is extremely dangerous. MBR viruses normally enter a system through a floppy disk that is installed in the floppy drive when the computer is started up. Even if the floppy disk is not bootable, it can infect the MBR. (n) (1) A set of symbols for representing something. For example, most computers use ASCII codes to represent characters. (2) Written computer instructions. The term code is somewhat colloquial. For example, a programmer might say: "I wrote a lot of code this morning" or "There's one piece of code that doesn't work." Code can appear in a variety of forms. The code that a programmer writes is called source code. After it has been compiled, it is called object code. Code that is ready to run is called executable code or machine code. (v) Colloquial for to program (that is, to write source code). A programmable machine. The two principal characteristics of a computer are:
Modern computers are electronic and digital. The actual machinery -- wires, transistors, and circuits -- is called hardware; the instructions and data are called software. All general-purpose computers require the following hardware components:
In addition to these components, many others make it possible for the basic components to work together efficiently. For example, every computer requires a bus that transmits data from one part of the computer to another. Computers can be generally classified by size and power as follows, though there is considerable overlap:
A complete, working computer. The computer system includes not only the computer, but also any software and peripheral devices that are necessary to make the computer function. Every computer system, for example, requires an operating system.
(v) (1) To copy a piece of data to a temporary location. In word processing, for example, copying refers to duplicating a section of a document and placing it in a buffer (sometimes called a clipboard). The term copy differs from cut, which refers to actually removing a section of a document and placing it in a buffer. After cutting or copying, you can move the contents of the buffer by pasting it somewhere else. (2) In file management, the term copy refers to making a duplicate of a file. (n) A duplicate of a piece of data, such as a file or a directory. (1) A symbol, name, or key that represents a list of commands, actions, or keystrokes. Many programs allow you to create macros so that you can enter a single character or word to perform a whole series of actions. Suppose, for example, that you are editing a file and want to indent every third line five spaces. If your word processor supports macros, you can create one that consists of the following keystrokes: Move Cursor to Beginning of Line Move Cursor Down 1 Line Move Cursor Down 1 Line Move Cursor Down 1 Line Insert 5 Spaces Now you can enter the name of the macro, and the word processor will perform all these commands at once. You can also use macros to enter words or phrases that you use frequently. For example, you could define a macro to contain all the keystrokes necessary to begin a letter -- your name, address, and a code that inserts the current date. Then, whenever you write a letter, you just press the macro key to include the letter header. In a way, macros are like simple programs or batch files. Some applications support sophisticated macros that even allow you to use variables and flow control structures such as loops. (2) In dBASE programs, a macro is a variable that points to another variable where the data is actually stored. In most other applications, this would be called a link.
Internal storage areas in the computer. The term memory identifies data storage that comes in the form of chips, and the word storage is used for memory that exists on tapes or disks. Moreover, the term memory is usually used as a shorthand for physical memory, which refers to the actual chips capable of holding data. Some computers also use virtual memory, which expands physical memory onto a hard disk. Every computer comes with a certain amount of physical memory, usually referred to as main memory or RAM. You can think of main memory as an array of boxes, each of which can hold a single byte of information. A computer that has 1 megabyte of memory, therefore, can hold about 1 million bytes (or characters) of information. There are several different types of memory:
A group of two or more computer systems linked together. There are many types of computer networks, including:
In addition to these types, the following characteristics are also used to categorize different types of networks:
Computers on a network are sometimes called nodes. Computers and devices that allocate resources for a network are called servers. The most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers. For large systems, the operating system has even greater responsibilities and powers. It is like a traffic cop -- it makes sure that different programs and users running at the same time do not interfere with each other. The operating system is also responsible for security, ensuring that unauthorized users do not access the system. Operating systems can be classified as follows:
Operating systems provide a software platform on top of which other programs, called application programs, can run. The application programs must be written to run on top of a particular operating system. Your choice of operating system, therefore, determines to a great extent the applications you can run. For PCs, the most popular operating systems are DOS, OS/2, and Windows, but others are available, such as Linux. As a user, you normally interact with the operating system through a set of commands. For example, the DOS operating system contains commands such as COPY and RENAME for copying files and changing the names of files, respectively. The commands are accepted and executed by a part of the operating system called the command processor or command line interpreter. Graphical user interfaces allow you to enter commands by pointing and clicking at objects that appear on the screen. (n) An organized list of instructions that, when executed, causes the computer to behave in a predetermined manner. Without programs, computers are useless. A program is like a recipe. It contains a list of ingredients (called variables) and a list of directions (called statements) that tell the computer what to do with the variables. The variables can represent numeric data, text, or graphical images. There are many programming languages -- C, C++, Pascal, BASIC, FORTRAN, COBOL, and LISP are just a few. These are all high-level languages. One can also write programs in low-level languages called assembly languages, although this is more difficult. Low-level languages are closer to the language used by a computer, while high-level languages are closer to human languages. Eventually, every program must be translated into a machine language that the computer can understand. This translation is performed by compilers, interpreters, and assemblers. When you buy software, you normally buy an executable version of a program. This means that the program is already in machine language -- it has already been compiled and assembled and is ready to execute. (v) To write programs. A database used by the Windows operating system (Windows 95 and NT ) to store configuration information. The Registry consists of the following major sections:
Most Windows applications write data to the Registry, at least during installation. You can edit the Registry directly by using the Registry Editor (regedit.exe) provided with the operating system. However, you must take great care because errors in the Registry could disable your computer.
Refers to techniques for ensuring that data stored in a computer cannot be read or compromised. Most security measures involve data encryption and passwords. Data encryption is the translation of data into a form that is unintelligible without a deciphering mechanism. A password is a secret word or phrase that gives a user access to a particular program or system. (1) A group of interdependent items that interact regularly to perform a task. (2) An established or organized procedure; a method. (3) A computer system refers to the hardware and software components that run a computer or computers. (4) An information system is a system that collects and stores data. (5) On Macintoshes, System is short for System file, an essential program that runs whenever you start up a Macintosh. The System provides information to all other applications that run on a Macintosh. The System and Finder programs together make up the Mac OS.
(6) System often simply refers to the operating system. The system tray is the area of the Start/Taskbar where the time and date are displayed. An imaginary memory area located as a file on the Hard Drive which is supported by some operating systems (for example, Windows but not DOS) in conjunction with the hardware. You can think of virtual memory as an alternate set of memory addresses (RAM). Programs use these virtual addresses rather than real addresses to store instructions and data. When the program is actually executed, the virtual addresses (Space within the swap file on the hard drive) are converted into real memory addresses (RAM). The purpose of virtual memory is to enlarge the address space, the set of addresses a program can utilize. For example, virtual memory might contain twice as many addresses as main memory. A program using all of virtual memory, therefore, would not be able to fit in main memory all at once. Nevertheless, the computer could execute such a program by copying into main memory those portions of the program needed at any given point during execution. To facilitate copying virtual memory into real memory, the operating system divides virtual memory into pages, each of which contains a fixed number of addresses. Each page is stored on a disk until it is needed. When the page is needed, the operating system copies it from disk to main memory, translating the virtual addresses into real addresses. The process of translating virtual addresses into real addresses is called mapping. The copying of virtual pages from disk to main memory is known as paging or swapping.
(1) A program or algorithm that replicates itself over a computer network and usually performs malicious actions, such as using up the computer's resources and possibly shutting the system down. Also see virus. (2) When used in all capital letters, WORM is an acronym for for write once, read many, an optical disk technology that allows you to write data onto a disk just once. After that, the data is permanent and can be read any number of times. Unlike CD-ROMs, there is no single standard for WORM disks, which means that they can only be read by the same type of drive that wrote them. This has hampered their acceptance, although they have found a niche market as an archival media. WORM is also called CD-R.
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