Abort
To stop a program or function before it has finished naturally. The term abort refers to both requested and unexpected terminations. For example, many applications let you abort a search or a print job.

When a program aborts, you are usually returned to the operating system shell level. Contrast abort with crash, which makes the entire system, including the operating system, unusable.

Background
(1) Multitasking computers are capable of executing several tasks, or programs, at the same time. In some multitasking systems, one of the processes is called the foreground process , and the others are called background processes.

The foreground process is the one that accepts input from the keyboard, mouse, or other input device. Background processes cannot accept interactive input from a user, but they can access data stored on a disk and write data to the video display. For example, some word processors print files in the background, enabling you to continue editing while files are being printed. This is called print spooling . In addition, many communications programs are designed to run in the background. Background processes generally have a lower priority than foreground processes so that they do not interfere with interactive applications.

Even though DOS is not a multitasking operating system, it can perform some specialized tasks, such as printing, in the background. Operating environments, such as Microsoft Windows and the Macintosh operating system, provide a more general multitasking environment.

(2) The area of a display screen not covered by characters and graphics. The background is like a canvas on top of which characters and graphics are placed. Some monitors allow you to control the color or shading of the background.

Batch File
A file that contains a sequence, or batch, of commands. Batch files are useful for storing sets of commands that are always executed together because you can simply enter the name of the batch file instead of entering each command individually.

Whenever you boot a DOS -based computer, the system automatically executes the batch file named AUTOEXEC.BAT, if it exists.

Many operating systems use the terms command file or shell script in place of batch file.

Batch Processing
Executing a series of noninteractive jobs all at one time. The term originated in the days when users entered programs on punch cards. They would give a batch of these programmed cards to the system operator, who would feed them into the computer.

Usually, batch jobs are stored up during working hours and then executed during the evening or whenever the computer is idle. Batch processing is particularly useful for operations that require the computer or a peripheral device for an extended period of time. Once a batch job begins, it continues until it is done or until an error occurs. Note that batch processing implies that there is no interaction with the user while the program is being executed.

The opposite of batch processing is transaction processing or interactive processing. In interactive processing, the application responds to commands as soon as you enter them.

BeOS
An operating system developed by Be, Inc. that runs on the PowerPC platform and Intel x86 processors. Despite being smaller than other modern operating systems, such as the Mac OS and Windows, BeOS nevertheless sports a modern graphical user interface (GUI), preemptive multitasking, multithreading, and built-in support for symmetric multiprocessing (SMP).

BIOS
Pronounced "bye-ose," an acronym for basic input/output system. The BIOS is built-in software that determines what a computer can do without accessing programs from a disk. On PCs, the BIOS contains all the code required to control the keyboard, display screen, disk drives, serial communications, and a number of miscellaneous functions.

The BIOS is typically placed in a ROM chip that comes with the computer (it is often called a ROM BIOS). This ensures that the BIOS will always be available and will not be damaged by disk failures. It also makes it possible for a computer to boot itself. Because RAM is faster than ROM, though, many computer manufacturers design systems so that the BIOS is copied from ROM to RAM each time the computer is booted. This is known as shadowing.

Many modern PCs have a flash BIOS, which means that the BIOS has been recorded on a flash memory chip, which can be updated if necessary.

The PC BIOS is fairly standardized, so all PCs are similar at this level (although there are different BIOS versions). Additional DOS functions are usually added through software modules. This means you can upgrade to a newer version of DOS without changing the BIOS.

PC BIOSes that can handle Plug-and-Play (PnP) devices are known as PnP BIOSes, or PnP-aware BIOSes. These BIOSes are always implemented with flash memory rather than ROM.

Blue Screen Of Death
An error that can appear on computers running in a Windows' environment. This includes even the earliest versions of Windows such as Windows 3.0 and 3.1, and still occurs in later versions such as Microsoft Windows 95, Windows 98, Windows NT, and Windows 2000 beta. Jokingly called the blue screen of death because when the error occurs, the screen turns blue, and the computer almost always freezes and requires rebooting.

Boot
To load the first piece of software that starts a computer. Because the operating system is essential for running all other programs, it is usually the first piece of software loaded during the boot process.

Boot is short for bootstrap, which in olden days was a strap attached to the top of your boot that you could pull to help get your boot on. Hence, the expression "pull oneself up by the bootstraps." Similarly, bootstrap utilities help the computer get started.

Short for bootstrap, the starting-up of a computer, which involves loading the operating system and other basic software. A cold boot is when you turn the computer on from an off position. A warm boot is when you reset a computer that is already on.

Bootable Diskette
A diskette from which you can boot your computer. Normally, your computer boots from a hard disk, but if the hard disk is damaged (for example, by a virus), you can boot the computer from a bootable diskette. For this reason, it's a good idea to make sure you always have a bootable diskette on hand.

A bootable diskette is also called a bootable floppy, boot disk, and startup disk.

CLDC
Short for Connected Limited Device Configuration. CLDC is the J2ME configuration for smaller handheld devices that are usually battery operated and low in memory with limited processing power and low bandwidth.

Most often the CLDC uses the K virtual machine, which is suitable for devices with 16/32-bit RISC/CISC microprocessors/controllers, and with as little as 160 K of total memory available -- 128 K of which is for the storage of the actual virtual machine and libraries themselves.

CLDC reference implementation and KVM runs on Windows 98/NT, Solaris, and Palm platforms. Developers can access binary releases of the CLDC, or they can get the full release by signing legal forms from Sun.

Clean Boot
Starting (booting) a computer as minimalistically as possible. Typically when you start your computer, it loads many files and programs to customize your environment. A clean boot eliminates these optional features and loads only those files and programs that are absolutely required by the operating system.

A clean boot is a troubleshooting technique that allows you to get the computer up and running so that you can perform diagnostic tests to determine which elements of the normal boot process are causing problems.

Cold Boot
The start-up of a computer from a powered-down state.

Command
An instruction to a computer or device to perform a specific task.

Every program that interacts with people responds to a specific set of commands. The set of commands and the syntax for entering them is called the user interface and varies from one program to another.

The DOS operating system makes a distinction between internal and external commands. Internal commands are commands, such as COPY and DIR, that can be handled by the COMMAND.COM program. External commands include the names of all other COM files, as well as EXE and BAT files.

Command Buffer
A temporary storage area where commands are kept. (In DOS environments, the command buffer is called a template.) DOS and UNIX support several operations for manipulating the command buffer. For example, you can use the F3 function key in DOS to copy the template 's contents to the display screen. This is useful for repeating a command or for correcting a mistake.

Command Language
The programming language through which a user communicates with the operating system or an application. For example, the DOS command language includes the commands DIR, COPY, and DEL, to name a few. The part of an operating system that responds to operating system commands is called the command processor.

With graphical user interfaces, the command language consists of operations you perform with a mouse or similar input device.

Command Line
The line on the display screen where a command is expected. Generally, the command line is the line that contains the most recently displayed command prompt.

Command Processor
The part of the operating system that receives and executes operating system commands. Every operating system has a command processor. When the command prompt is displayed, the command processor is waiting for a command. After you enter a command, the command processor analyzes the syntax to make sure the command is valid, and then either executes the command or issues an error warning. For operating systems with a graphical user interface, the command processor interprets mouse operations and executes the appropriate command.

Configuration File
A file that contains configuration information for a particular program. When the program is executed, it consults the configuration file to see what parameters are in effect. The configuration file for DOS is called CONFIG.SYS. Older versions of the Windows operating system stores configuration information in files with a.INI extension. The two most important configuration files are WIN.INI and SYS.INI. Starting with Windows 95, most configuration information is stored in MIF files and in the Registry.

Control Panel
A Macintosh utility that permits you to set many of the system parameters. For example, you can control the type of beeps the Mac makes and the sensitivity of the mouse. On older Macs (system 6 and earlier), control panels are called cdevs.

The Windows operating system has a Control Panel program that offers many of the same features as the Macintosh control panels.

Control Program
(1) A program that enhances an operating system by creating an environment in which you can run other programs. Control programs generally provide a graphical interface and enable you to run several programs at once in different windows.

Control programs are also called operating environments.

(2) Another term for operating system.

Cooperative Multi-Tasking
A type of multitasking in which the process currently controlling the CPU must offer control to other processes. It is called cooperative because all programs must cooperate for it to work. If one program does not cooperate, it can hog the CPU. In contrast, preemptive multitasking forces applications to share the CPU whether they want to or not. Both the Macintosh and Windows 3.x operating systems are based on cooperative multitasking, whereas UNIX, Windows 95, Windows NT, and OS/2 are based on preemptive multitasking.

CP/M
Abbreviation of Control Program for Microprocessors. Created by Digital Research Corporation, CP/M was one of the first operating systems for personal computers. However, Digital Research Corporation made a critical strategic error by not agreeing to produce an operating system for the first IBM PC. According to the folklore, the president of Digital Research was flying his airplane when IBM came to call. IBM marched out and never looked back.

Instead, IBM turned to Microsoft Corporation, which developed MS-DOS. By the mid 1980s, MS-DOS had become the standard operating system for IBM-compatible personal computers. CP/M is now obsolete.

Cross-Platform
Refers to the capability of software or hardware to run identically on different platforms. Many applications for Windows and the Macintosh, for example, now produce binary-compatible files, which means that users can switch from one platform to the other without converting their data to a new format.

Cross-platform computing is becoming increasingly important as local-area networks become better at linking machines of different types.

Distributed Processing
Refers to any of a variety of computer systems that use more than one computer, or processor, to run an application. This includes parallel processing, in which a single computer uses more than one CPU to execute programs. More often, however, distributed processing refers to local-area networks (LANs) designed so that a single program can run simultaneously at various sites. Most distributed processing systems contain sophisticated software that detects idle CPUs on the network and parcels out programs to utilize them.

Another form of distributed processing involves distributed databases, databases in which the data is stored across two or more computer systems. The database system keeps track of where the data is so that the distributed nature of the database is not apparent to users.

Driver
A program that controls a device. Every device, whether it be a printer, disk drive, or keyboard, must have a driver program. Many drivers, such as the keyboard driver, come with the operating system. For other devices, you may need to load a new driver when you connect the device to your computer. In DOS systems, drivers are files with a.SYS extension. In Windows environments, drivers often have a.DRV extension.

A driver acts like a translator between the device and programs that use the device. Each device has its own set of specialized commands that only its driver knows. In contrast, most programs access devices by using generic commands. The driver, therefore, accepts generic commands from a program and then translates them into specialized commands for the device.

Embedded Object
An object created with one application and embedded into a document created by another application. Embedding the object, rather than simply inserting or pasting it, ensures that the object retains its original format. In fact, you can modify the embedded object with the original program. In Windows environments, embedding objects is made possible by a technology called OLE.

Environment
(1) The state of a computer, usually determined by which programs are running and basic hardware and software characteristics. For example, when one speaks of running a program in a UNIX environment, it means running a program on a computer that has the UNIX operating system.

One ingredient of an environment, therefore, is the operating system. But operating systems include a number of different parameters. For example, many operating systems allow you to choose your command prompt or a default command path. All these parameters taken together constitute the environment.

Another term for environment in this sense is platform.

(2) In DOS systems, the environment is an area in memory that the operating system and other programs use to store various types of miscellaneous information. For example, your word processor may use the environment area to store the location of backup files. You can view or modify the environment with the SET command.

EPOC
An operating system from Psion Software, designed specifically for mobile, ROM -based computing devices. EPOC16 is a 16-bit version of the operating system that has been available for several years and is embedded in many handheld devices. EPOC32 is a newer, 32-bit operating system that supports preemptive multitasking. EPOC is competing head-to-head with Windows CE in the grow PDA market.

Event
An action or occurrence detected by a program. Events can be user actions, such as clicking a mouse button or pressing a key, or system occurrences, such as running out of memory. Most modern applications, particularly those that run in Macintosh and Windows environments, are said to be event-driven, because they are designed to respond to events.

Executable File
A file in a format that the computer can directly execute. Unlike source files, executable files cannot be read by humans. To transform a source file into an executable file, you need to pass it through a compiler or assembler.

In DOS systems, executable files have either a.COM or.EXE extension and are called COM files and EXE files, respectively.

Execute
Same as run. Execute means to perform an action, as in executing a program or a command.

Fault Tolerance
The ability of a system to respond gracefully to an unexpected hardware or software failure. There are many levels of fault tolerance, the lowest being the ability to continue operation in the event of a power failure. Many fault-tolerant computer systems mirror all operations -- that is, every operation is performed on two or more duplicate systems, so if one fails the other can take over.

File Handle
A number that the operating system assigns temporarily to a file when it is opened. The operating system uses the file handle internally when accessing the file. A special area of main memory is reserved for file handles, and the size of this area determines how many files can be open at once. In DOS and Windows, you can set the maximum number of open files with the FILES= statement in CONFIG.SYS

Foreground
(1) In multiprocessing systems, the process that is currently accepting input from the keyboard or other input device is sometimes called the foreground process.

(2) On display screens, the foreground consists of the characters and pictures that appear on the screen. The background is the uniform canvas behind the characters and pictures.

GNOME
Acronym for GNU Network Object Model Environment. (Pronounced guh-nome.) GNOME is part of the GNU project and part of the free software, or open source, movement. GNOME is a Windows-like desktop system that works on UNIX and UNIX-like systems and is not dependent on any one window manager. The current version runs on Linux, FreeBSD, IRIX and Solaris. The main objective of GNOME is to provide a user-friendly suite of applications and an easy-to-use desktop.

GPF
Short for General Protection Fault, a computer condition that causes a Windows application to crash. The most common cause of a GPF is two applications trying to use the same block of memory, or more specifically, one application trying to use memory assigned to another application.

Interrupt
A signal informing a program that an event has occurred. When a program receives an interrupt signal, it takes a specified action (which can be to ignore the signal). Interrupt signals can cause a program to suspend itself temporarily to service the interrupt.

Interrupt signals can come from a variety of sources. For example, every keystroke generates an interrupt signal. Interrupts can also be generated by other devices, such as a printer, to indicate that some event has occurred. These are called hardware interrupts. Interrupt signals initiated by programs are called software interrupts. A software interrupt is also called a trap or an exception.

PCs support 256 types of software interrupts and 15 hardware interrupts. Each type of software interrupt is associated with an interrupt handler -- a routine that takes control when the interrupt occurs. For example, when you press a key on your keyboard, this triggers a specific interrupt handler. The complete list of interrupts and associated interrupt handlers is stored in a table called the interrupt vector table, which resides in the first 1 K of addressable memory.

Interrupt Vector Table
A table of interrupt vectors (pointers to routines that handle interrupts). On PCs, the interrupt vector table consists of 256 4-byte pointers, and resides in the first 1 K of addressable memory. Each interrupt number is reserved for a specific purpose. For example, 16 of the vectors are reserved for the 16 IRQ lines.

J2ME
Short for Java 2 Platform Micro Edition. J2ME is Sun Microsystems' answer to a consumer wireless device platform. J2ME allows developers to use Java and the J2ME wireless toolkit to create applications and programs for wireless and mobile devices.

J2ME consists of two elements -- configurations and profiles.

Configurations provide a set of libraries and a virtual machine for a category of wireless device. There are two configurations for J2ME, one for fixed wireless devices and one for mobile wireless devices.

Profiles are APIs built on top of configurations to provide a runtime environment for a specific device, such as a PDA, cellphone, or set-top box. The profile manages the application, user interface, networking and I/O.

In order to support Java apps, manufacturers need to implement a profile for their specific devices.

Job
A task performed by a computer system. For example, printing a file is a job. Jobs can be performed by a single program or by a collection of programs.

JVM
Acronym for Java Virtual Machine. An abstract computing machine, or virtual machine, JVM is a platform-independent programming language that converts Java bytecode into machine language and executes it. Most programming languages compile source code directly into machine code that is designed to run on a specific microprocessor architecture or operating system, such as Windows or UNIX. A JVM -- a machine within a machine -- mimics a real Java processor, enabling Java bytecode to be executed as actions or operating system calls on any processor regardless of the operating system. For example, establishing a socket connection from a workstation to a remote machine involves an operating system call. Since different operating systems handle sockets in different ways, the JVM translates the programming code so that the two machines that may be on different platforms are able to connect.

KDE
Acronym for K Desktop Environment. A network-transparent contemporary desktop environment for UNIX workstations. KDE is part of the free software, or open source, movement, which competes with the more common commercial operating system /desktop platforms on the market. KDE is free to anyone and its source code is available to anyone to modify. Development of KDE takes place across the Internet where users share information with each other regarding current developments of the system.

Kernel
The central module of an operating system. It is the part of the operating system that loads first, and it remains in main memory. Because it stays in memory, it is important for the kernel to be as small as possible while still providing all the essential services required by other parts of the operating system and applications. Typically, the kernel is responsible for memory management, process and task management, and disk management.

Kernel32.dll
Kernel32.dll is the 32-bit dynamic link library found in the Windows operating system kernel. It handles memory management, input/output operations, and interrupts. When Windows boots up, kernel32.dll is loaded into a protected memory space so other applications do not take that space over.

On occasion, though, users may encounter the "invalid page fault" error.

This error occurs when a program or application tries to access kernel32.dll's protected memory space. Sometimes the error is caused by one particular program or application, and other times it is provoked by multiple files and applications.

If the problem results from running one application, then the application needs to be replaced. If the problem occurs when accessing multiple files and applications, the corruption is probably caused by faulty hardware.

Launch
To start a program.

Load
(1) To install. For example, to load a disk means to mount it in a disk drive.

(2) To copy a program from a storage device into memory. Every program must be loaded into memory before it can be executed. Usually the loading process is performed invisibly by a part of the operating system called the loader. You simply enter the name of the program you want to run, and the operating system loads it and executes it for you.

(3) In programming, load means to copy data from main memory into a data register.

(4) In networking, load refers to the amount of data (traffic) being carried by the network.

Loader
An operating system utility that copies programs from a storage device to main memory, where they can be executed. In addition to copying a program into main memory, the loader can also replace virtual addresses with physical addresses.

Most loaders are invisible: that is, you cannot directly execute them, but the operating system uses them when necessary.

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.

Memory Resident
Permanently in memory. Normally, a computer does not have enough memory to hold all the programs you use. When you want to run a program, therefore, the operating system is obliged to free some memory by copying data or programs from main memory to a disk. This process is known as swapping.

Certain programs, however, can be marked as being memory resident, which means that the operating system is not permitted to swap them out to a storage device; they will always remain in memory.

The programs and data used most frequently are the ones that should be memory resident. This includes central portions of the operating system and special programs, such as calendars and calculators, that you want to be able to access immediately.

Another term for memory resident is RAM resident. In DOS systems, memory-resident programs are called pop-up utilities or TSRs (terminate and stay resident).

Multiprocessing
(1) Refers to a computer system's ability to support more than one process (program) at the same time. Multiprocessing operating systems enable several programs to run concurrently. UNIX is one of the most widely used multiprocessing systems, but there are many others, including OS/2 for high-end PCs. Multiprocessing systems are much more complicated than single-process systems because the operating system must allocate resources to competing processes in a reasonable manner.

(2) Refers to the utilization of multiple CPUs in a single computer system. This is also called parallel processing.

Multi-Tasking
The ability to execute more than one task at the same time, a task being a program. The terms multitasking and multiprocessing are often used interchangeably, although multiprocessing sometimes implies that more than one CPU is involved.

In multitasking, only one CPU is involved, but it switches from one program to another so quickly that it gives the appearance of executing all of the programs at the same time.

There are two basic types of multitasking: preemptive and cooperative. In preemptive multitasking, the operating system parcels out CPU time slices to each program. In cooperative multitasking, each program can control the CPU for as long as it needs it. If a program is not using the CPU, however, it can allow another program to use it temporarily. OS/2, Windows 95, Windows NT, the Amiga operating system and UNIX use preemptive multitasking, whereas Microsoft Windows 3.x and the MultiFinder (for Macintosh computers) use cooperative multitasking.

Multi-Threading
The ability of an operating system to execute different parts of a program, called threads, simultaneously. The programmer must carefully design the program in such a way that all the threads can run at the same time without interfering with each other.

Multi-User
Refers to computer systems that support two or more simultaneous users. All mainframes and minicomputers are multi-user systems, but most personal computers and workstations are not. Another term for multi-user is time sharing.

MVS
Short for Multiple Virtual Storage, the operating system for older IBM mainframes. MVS was first introduced in 1974 and continues to be used, though it has been largely superseded by IBM's newer operating system, OS/390.

Native
Referring to an original form. For example, many applications can work with files in a variety of formats, but an application's native file format is the one it uses internally. For all other formats, the application must first convert the file to its native format.

NetWare
A popular local-area network (LAN) operating system developed by Novell Corporation. NetWare is a software product that runs on a variety of different types of LANs, from Ethernets to IBM token-ring networks. It provides users and programmers with a consistent interface that is independent of the actual hardware used to transmit messages.

Network Operating System
An operating system that includes special functions for connecting computers and devices into a local-area network (LAN). Some operating systems, such as UNIX and the Mac OS, have networking functions built in. The term network operating system, however, is generally reserved for software that enhances a basic operating system by adding networking features. For example, some popular NOS's for DOS and Windows systems include Novell Netware, Artisoft's LANtastic, Microsoft LAN Manager, and Windows NT.

NEXTSTEP
An object-oriented operating system developed by Next Inc., a company started in 1985 by Steven Jobs, one of the co-founders of Apple Computer. In 1997, Apple Computer acquired Next, with idea of making NextStep the foundation of its new Macintosh operating system.

NTLDR
Short for NT Loader, a program loaded from the hard drive boot sector that displays the Microsoft Windows NT startup menu and helps Windows NT load.

Often a user will see the message "NTLDR is Missing" after attempting to install Windows 2000 or Windows XP, or upgrade a Windows 95-based or Windows 98-based computer to Windows 2000 or Windows XP. The message appears after the first reboot. This occurs only if Windows 95 or 98 has been installed on a drive with the FAT32 file system.

To correct the problem, the user must boot the computer with a Windows 95 or 98 Startup diskette or another bootable diskette with sys.com on it. Then, at the "A:\>" prompt, type "sys c:" and press "enter." A "System Transferred" prompt should appear and then the user must reboot the computer without the diskette.

NTVDM
The NT Virtual DOS Machine (a.k.a WOW, or Windows on Windows), is a Win16 subsystem that runs under Windows NT, which allows 16-bit applications to run as if they were being executed on a DOS machine, with that machine's multitasking and segmented memory model.

Because the system is multitasked 16-bit DOS and Windows applications cannot crash NT. However, 16-bit apps within a Win16 subsystem run the exact same way as they do on a DOS/Win 3.x machine; therefore, 16-bit apps within the subsystem can crash one another, or the subsystem. To prevent this, you can launch multiple WOW subsystems as long as your program does not communicate using shared memory.

Windows NT will not allow NTVDM to execute instructions that try to directly manipulate hardware or memory locations. As a result, some DOS and Windows 3.x applications (such as games) may not run under Windows NT.

OpenDoc
A standard and application programming interface (API) that makes it possible to design independent programs (components) that can work together on a single document. OpenDoc is being developed by a loose alliance of companies, including Apple Computer, IBM, and Lotus. Notably absent from this list is Microsoft, which is pushing an alternative standard and API called Object Linking and Embedding (OLE).

Operating Environment
The environment in which users run programs. For example, the DOS environment consists of all the DOS commands available to users. The Macintosh environment, on the other hand, is a graphical user interface that uses icons and menus instead of commands.

There is a thin line between operating environments and shells. Historically, shells are the interfaces to operating systems. They do not actually add any new capabilities; they simply provide a better user interface. So-called intelligent shells, however, actually extend an operating system's capabilities, so there is little difference between intelligent shells and operating environments.

Operating environments are sometimes called control programs.

Operating System
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 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.

OS/2
An operating system for PCs developed originally by Microsoft Corporation and IBM, but sold and managed solely by IBM. OS/2 is compatible with DOS and Windows, which means that it can run all DOS and Windows programs. However, programs written specifically to run under OS/2 will not run under DOS or Windows.

Since its introduction in the late 80s, OS/2 has traveled a particularly rocky road. The first releases were hampered by a number of technical and marketing problems. Then Microsoft abandoned the project in favor of its own operating system solution, Microsoft Windows. That break spawned a feud between the two computer giants that is still being played out in many arenas.

OS/9
A real-time, multi-user, multitasking operating system developed by Microware Systems Corporation. Originally, OS-9 was a joint effort between Microware and Motorola. In the 1980's, Microware ported OS-9 to the Motorola 680x0 family of microprocessors, creating OS-9/68000, which is used in a variety of industrial and commercial arenas, including Philips' CD-I and, most recently, WebTV boxes.

Parallel Processing
The simultaneous use of more than one CPU to execute a program. Ideally, parallel processing makes a program run faster because there are more engines (CPUs) running it. In practice, it is often difficult to divide a program in such a way that separate CPUs can execute different portions without interfering with each other.

Most computers have just one CPU, but some models have several. There are even computers with thousands of CPUs. With single-CPU computers, it is possible to perform parallel processing by connecting the computers in a network. However, this type of parallel processing requires very sophisticated software called distributed processing software.

Note that parallel processing differs from multitasking, in which a single CPU executes several programs at once.

Parallel processing is also called parallel computing.

Pheonix BIOS
Phoenix Corporation one of the largest producers of BIOS firmware for IBM PC clones.

Pipe
A temporary software connection between two programs or commands. Normally, the operating system accepts input from the keyboard and sends output to the display screen. Sometimes, however, it is useful to use the output from one command as the input for a second command, without passing the data through the keyboard or display screen. Pipes were invented for these situations.

One of the best examples of pipe usage is linking the command that lists files in a directory to a command that sorts data. By piping the two commands together, you can display the files in sorted order. In UNIX and DOS, the pipe symbol is a vertical bar (|).

Platform
The underlying hardware or software for a system. For example, the platform might be an Intel 80486 processor running DOS Version 6.0. The platform could also be UNIX machines on an Ethernet network.

The platform defines a standard around which a system can be developed. Once the platform has been defined, software developers can produce appropriate software and managers can purchase appropriate hardware and applications. The term is often used as a synonym of operating system.

The term cross-platform refers to applications, formats, or devices that work on different platforms. For example, a cross-platform programming environment enables a programmer to develop programs for many platforms at once.

PnP
Short for Plug and Play, a technology developed by Microsoft and Intel that supports plug-and-play installation. PnP is built into the Windows 95 operating system, but to use it, the computer's BIOS and expansion boards must also support PnP.

Pop-Up Utility
A program installed to be memory resident so that you can always execute it by pressing a special key, called a hot key. When you press the hot key, the pop-up utility appears, regardless of which application you are currently running. When you exit the pop-up utility, the system returns you to your previous program.

In DOS systems, pop-up utilities are also called TSRs.

Process
An executing program. The term is used loosely as a synonym of task.

To perform some useful operations on data.

Real Time
Occurring immediately. The term is used to describe a number of different computer features. For example, real-time operating systems are systems that respond to input immediately. They are used for such tasks as navigation, in which the computer must react to a steady flow of new information without interruption. Most general-purpose operating systems are not real-time because they can take a few seconds, or even minutes, to react.

Real time can also refer to events simulated by a computer at the same speed that they would occur in real life. In graphics animation, for example, a real-time program would display objects moving across the screen at the same speed that they would actually move.

Reboot
To restart a computer. In DOS, you can reboot by pressing the Alt, Control and Delete keys simultaneously. This is called a warm boot. You can also perform a cold boot by turning the computer off and then on again.

On Macs, you reboot by selecting the "Restart" option from the Special menu.

Resource
(1) Generally, any item that can be used. Devices such as printers and disk drives are resources, as is memory.

(2) In many operating systems, including Microsoft Windows and the Macintosh operating system, the term resource refers specifically to data or routines that are available to programs. These are also called system resources.

Segment
(1) In networks, a section of a network that is bounded by bridges, routers, hubs, or switches. Dividing an Ethernet into multiple segments is one of the most common ways of increasing bandwidth on the LAN. If segmented correctly, most network traffic will remain within a single segment, enjoying the full 10 Mbps bandwidth. Hubs and switches are used to connect each segment to the rest of the LAN.

(2) In virtual memory systems, a variable-sized portion of data that is swapped in and out of main memory. Contrast with page.

(3) In graphics, a piece of a polyline, which is a fixed-sized portion of data.

Shell
(1) The outermost layer of a program. Shell is another term for user interface. Operating systems and applications sometimes provide an alternative shell to make interaction with the program easier. For example, if the application is usually command driven, the shell might be a menu-driven system that translates the user's selections into the appropriate commands.

(2) Sometimes called command shell, a shell is the command processor interface. The command processor is the program that executes operating system commands. The shell, therefore, is the part of the command processor that accepts commands. After verifying that the commands are valid, the shell sends them to another part of the command processor to be executed.

UNIX systems offer a choice between several different shells, the most popular being the Cshell, the Bourne shell, and the Korn shell. Each offers a somewhat different command language.

SMP
(1) Short for Symmetric Multiprocessing, a computer architecture that provides fast performance by making multiple CPUs available to complete individual processes simultaneously (multiprocessing). Unlike asymmetrical processing, any idle processor can be assigned any task, and additional CPUs can be added to improve performance and handle increased loads. A variety of specialized operating systems and hardware arrangements are available to support SMP. Specific applications can benefit from SMP if the code allows multithreading.

SMP uses a single operating system and shares common memory and disk input/output resources. Both UNIX and Windows NT support SMP.

(2) Short for Simple Management Protocol, another name for SNMP2. SNMP2 is an enhanced version of the Simple Network Management Protocol (SNMP) with features required to support larger networks operating at high data transmission rates. SNMP2 also supports multiple network management workstations organized in a hierarchical fashion.

Spooling
Acronym for simultaneous peripheral operations on-line, spooling refers to putting jobs in a buffer, a special area in memory or on a disk where a device can access them when it is ready. Spooling is useful because devices access data at different rates. The buffer provides a waiting station where data can rest while the slower device catches up.

The most common spooling application is print spooling. In print spooling, documents are loaded into a buffer (usually an area on a disk), and then the printer pulls them off the buffer at its own rate. Because the documents are in a buffer where they can be accessed by the printer, you can perform other operations on the computer while the printing takes place in the background. Spooling also lets you place a number of print jobs on a queue instead of waiting for each one to finish before specifying the next one.

Swap File
In Windows environments, a hidden file used by the operating system for swapping.

System Call
The invocation of an operating system routine. Operating systems contain sets of routines for performing various low-level operations. For example, all operating systems have a routine for creating a directory. If you want to execute an operating system routine from a program, you must make a system call.

System Tray
Introduced with Windows, the system tray is located in the Windows taskbar (usually at the bottom next to the clock) and contains miniature icons for easy access to system functions such as fax, printer, modem, volume, and more. Double click or right click on an icon to view and access the details and controls.

Systems Software
Refers to the operating system and all utility programs that manage computer resources at a low level. Software is generally divided into systems software and applications software. Applications software comprises programs designed for an end user, such as word processors, database systems, and spreadsheet programs. Systems software includes compilers, loaders, linkers, and debuggers.

Task
An operating system concept that refers to the combination of a program being executed and bookkeeping information used by the operating system. Whenever you execute a program, the operating system creates a new task for it. The task is like an envelope for the program: it identifies the program with a task number and attaches other bookkeeping information to it.

Many operating systems, including UNIX, OS/2, and Windows, are capable of running many tasks at the same time and are called multitasking operating systems.

In most operating systems, there is a one-to-one relationship between the task and the program, but some operating systems allow a program to be divided into multiple tasks. Such systems are called multithreading operating systems.

The terms task and process are often used interchangeably, although some operating systems make a distinction between the two.

Task Switching
Refers to operating systems or operating environments that enable you to switch from one program to another without losing your spot in the first program. Many utilities are available that add task switching to DOS systems.

Note that task switching is not the same as multitasking. In multitasking, the CPU switches back and forth quickly between programs, giving the appearance that all programs are running simultaneously. In task switching, the CPU does not switch back and forth, but executes only one program at a time. Task switching does allow you to switch smoothly from one program to another.

Task switching is sometimes called context switching.

Thread
(1) In online discussions, a series of messages that have been posted as replies to each other. A single forum or conference typically contains many threads covering different subjects. By reading each message in a thread, one after the other, you can see how the discussion has evolved. You can start a new thread by posting a message that is not a reply to an earlier message.

(2) In programming, a part of a program that can execute independently of other parts. Operating systems that support multithreading enable programmers to design programs whose threaded parts can execute concurrently.

Time Sharing
Refers to the concurrent use of a computer by more than one user -- users share the computer's time. Time sharing is synonymous with multi-user. Almost all mainframes and minicomputers are time-sharing systems, but most personal computers and workstations are not.

Transaction Processing
A type of computer processing in which the computer responds immediately to user requests. Each request is considered to be a transaction. Automatic teller machines for banks are an example of transaction processing.

The opposite of transaction processing is batch processing, in which a batch of requests is stored and then executed all at one time. Transaction processing requires interaction with a user, whereas batch processing can take place without a user being present.

Utility
A program that performs a very specific task, usually related to managing system resources. Operating systems contain a number of utilities for managing disk drives, printers, and other devices.

Utilities differ from applications mostly in terms of size, complexity and function. For example, word processors, spreadsheet programs, and database applications are considered applications because they are large programs that perform a variety of functions not directly related to managing computer resources.

Utilities are sometimes installed as memory-resident programs. On DOS systems, such utilities are called TSRs.

Virtual Device Driver
In Windows systems, a special type of device driver that has direct access to the operating system kernel. This allows them to interact with system and hardware resources at a very low level.

In Windows 95, virtual device drivers are often called VxDs because the filenames end with the .vxd extension.

Virtual Machine
A self-contained operating environment that behaves as if it is a separate computer. For example, Java applets run in a Java virtual machine (VM) that has no access to the host operating system.

VMM32.vxd
Found in Windows 9x machines, VMM32.vxd is the virtual device driver library that contains virtual device driver files needed for system start up.

VMM32.vxd is different for every machine; therefore, if it gets corrupted, it cannot be copied from another computer; it'll need to be rebuilt.

VMS
Short for Virtual Memory System, a multi-user, multitasking, virtual memory operating system that runs on DEC's VAX and Alpha lines of minicomputers and workstations. VMS was introduced in 1979 along with the first VAX minicomputer. Like the VAX itself, VMS has undergone many changes over the years. DEC now refers to it as OpenVMS.

Warm Boot
Refers to resetting a computer that is already turned on. Resetting it returns the computer to its initial state, and any data or programs in main memory are erased. A warm boot is sometimes necessary when a program encounters an error from which it cannot recover. On PCs, you can perform a warm boot by pressing the Control, Alt, and Delete keys simultaneously. On Macs, you can perform a warm boot by pressing the Restart button.

A cold boot refers to turning a computer on from an off position.

WDM
(1) Short for wavelength division multiplexing, a type of multiplexing developed for use on optical fiber. WDM modulates each of several data streams onto a different part of the light spectrum. WDM is the optical equivalent of FDM.

(2) Short for Windows Driver Model, a driver technology developed by Microsoft to create drivers that are source-code compatible for Windows 98, 2000, Me and XP.

WDM works by channeling some of the work of the device driver into portions of the code that are integrated into the operating system. These portions of code handle all of the low-level buffer management, including DMA and Plug and Play device enumeration. The WDM device driver becomes more streamlined with less code and works at greater efficiency.

All versions of Microsoft Windows after Windows 95 have implemented WDM. Kernel-mode drivers that follow WDM rules are called WDM drivers.

Win.com
Win.com is the executable file responsible for Windows start-up. It runs after the autoexec.bat file is processed, and it accesses the VMM32.vxd file.

In a Windows 3.x environment, the win.com file is executed by typing "win" in the DOS prompt. In version 9x OSs, win.com runs automatically.

Windows 2000
A product in Microsoft's Windows line of operating systems.Windows 2000 is sometimes abbreviated as W2K.

Windows XP
An operating system introduced in 2001 from Microsoft's Windows family of operating systems, the previous version of Windows being Windows Me. Microsoft called the release its most important product since Windows 95. Along with a redesigned look and feel to the user interface, the new operating system is built on the Windows 2000 kernel, giving the user a more stable and reliable environment than previous versions of Windows. Windows XP comes in two version, Home and Professional. Where the Professional Edition focuses on reliability and security, the Home Edition includes extensive digital photography, digital music, digital video, home networking and communications features. The company has also focused on mobility for both editions, including plug and play features for connecting to wireless networks. The operating system also utilizes the 802.1x wireless security standard.