LIS 505 - Operating systems

systems software

Software that manages computer resources at a low level. May also include tools used by programmers (compilers, linkers, loaders, and debuggers) and some utilities.

operating systems

Software that performs basic tasks, such as recognizing input, sending output, keeping track of files and directories, controlling peripheral devices, making sure that different programs running at the same time do not interfere with each other and that unauthorized users do not access the system.


A family of operating systems from Microsoft. It dominates the personal computer market.


A family of operating systems originating with Bell Labs in the 1970s. Versions are widely used on workstations and larger computers.


A freely-distributable Unix-like operating system available for a variety of different computers, including personal computers.


The parts of operating systems that load first and remain in memory.


Loading software required to start the computer (typically, the operating system). Short for bootstrapping, from the phrase "lifting oneself up by one's own bootstraps".

user interfaces

The ways users communicate with computers and computers with users; for example, through commands and prompts, or mouse clicks and graphic displays.


Categories of underlying hardware or software configurations for computer systems. Usually defined in terms of the operating system.


Output messages indicating that a computer is waiting for input.


Messages input by a user instructing a computer or device to perform specific tasks.

graphical user interfaces

GUIs. User interfaces that take advantage of a computer's graphics capabilities to make interaction easier. They typically make use of windows, icons, mice, and pointers (WIMP).


Small pictures that represent various entities such as programs and that normally respond to mouse clicks in a graphical user interface.


Lists of options from which the user can choose.

pull-down menus

Menus that appear just below items when they are selected, usually by left-clicking on them with a mouse.

pop-up menus

Menus that appear temporarily at various places on a screen, such as those that appear in many Windows applications when the user right-clicks on objects.

operating environments

Interfaces through which users run programs. Also referred to as shells, especially when part of the operating system. .

plug and play

The ability of a computer system to configure devices automatically. . Microsoft and Intel's PnP technology allows plug and play in Windows 95 and later versions for devices that support PnP. .


Short for Object Linking and Embedding, A Microsoft standard that allows the user to embed an object created with one application program in a file created with another application program. The user needs to have the program that created an embedded object in order to view or edit the object. . Linking is an option that also includes in the document a reference to another file that contains the original object; if that file is updated, the object embedded in the document will be updated automatically.

dual-boot systems

Computer systems in which two operating systems are installed on the hard drive; when users start these systems, a boot manager program displays a menu, allowing them to choose which operating system they want.

network operating systems

NOSs. Operating systems with special functions for connecting computers and devices into local area networks. Not usually applied to general operating systems with built-in networking functions. .


Executing more than one task (program) at the same time. Also referred to as multiprogramming or, especially when more than one CPU is used, multiprocessing. .


Concurrent use of a computer by more than one user. Typical of larger computer systems.

memory protection

An operating system feature by which each program can be allocated a certain section of memory that other programs cannot use. A feature of the protected mode that is available on Intel processors from the 80286 on.

response time

The time between the end of a user's demand on a computer system and the beginning of a response. whatis?com


Signals informing programs that certain kinds of events have occurred and causing control to pass to special routines (interrupt handlers). Intel processors support only 15 hardware interrupts, and allocating these among the devices that need them on a given computer system can be tricky.

virtual memory

A combination of real memory and disk storage that an operating system makes look like a larger real memory to software.


A technique, used by some virtual memory systems, which divides virtual memory into pages, some of which are in real memory while others are on disk. When a page is needed that is not in real memory, a page fault is said to occur, and the operating system tries to get the missing page from the disk.


In virtual memory systems, spending too much time swapping pages and not enough time doing actual work, typically because too many programs are competing for too little memory.


Putting jobs in a special area where a device, such as a printer, can access them when it is ready.


Programs that perform very specific tasks.

file managers

Utilities that allow users to perform basic file functions such as locating, copying, moving, deleting, viewing, editing, and executing. Google

backup and restore utilities

Utilities that allow users to copy files to and from another (backup) medium, such as disk or tape. Google

file compression utilities

Utilities that allow users to store file contents in a format that requires less space. Google

disk defragmenters

Utilities that optimize disks by reducing fragmentation of files, a condition in which pieces of a file are scattered around in different places.

device drivers

Special programs that control devices and are often parts of operating systems. They are needed in order for other programs to communicate with the devices. Windows driver files are not normal executable programs and do not have the extension .exe or .com; typical extensions are .vxd, .drv, and .sys.

Last updated October 30, 2003.
This page maintained by Prof. Tim Craven
E-mail (text/plain only):
Faculty of Information and Media Studies
University of Western Ontario,
London, Ontario
Canada, N6A 5B7