They are important because
the performance of the operating system has a dramatic influence on the quality of the computer user??™s experience
and the efficiency of the computer system as a whole. In the days of simpler computing systems, in the
1960s and 1970s, a company might purchase a computer without an operating system, with the intention
of writing or using its own operating system, but today one always buys an operating system when one buys
a computer.
The operating system provides easy access to peripheral devices like printers and displays, a file system for
storing information like data, documents, and programs, a user interface to make it easy to start application
programs, a time-of-day clock, a connection to the Internet using the standard network protocols, a set of ???calls???
or ???methods??? that application programs can use to request services of the operating system, an efficient algorithm
for allocating memory to the various programs active at the same time, and an efficient algorithm for sharing
access to the computer among several people and/or programs at the same time.
Popular operating systems today include Microsoft Windows, Mac OS, Unix, Linux (a variety of Unix),
and IBM??™s MVS, among others.
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