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Operating systems


An operating system is a computer program which manages a computer's resources
and acts as a software bridge between client applications and the computer
itself. It is the most fundamental piece of software which runs on a system
and is responsible for starting and supporting the execution of all other
programs. Simple operating systems (such as MS-DOS) only allow a single client
program to execute at once. The main resources controlled by the operating
system are file storage and access to other basic system devices such as the
console screen and keyboard. More sophisticated operating systems (such as
OS/2, MS-DOS/Microsoft Windows and Apple's System 7) allow more than one
program to run at once. Such operating systems are said to be multi-tasking
and are capable of dividing the resources of the computer between several
executing programs (or processes). Some operating systems (such as UNIX,
Novell NetWare and VMS) also allow multiple users to use the same computer at
the same time. These are referred to as being multi-user. They incorporate
security facilities so that different people using the computer can co-operate
in an ordered fashion.

In the 1970's virtually all computing was done on large centralised mainframes
and mini-computers, most of which ran multi-user, multi-tasking operating
systems and were capable of interactive use. Typically, users used terminals,
communications devices which act much like telephones, merely accepting input
(from the keyboard), sending it off the central system (where all processing
took place), then displaying on it screen output characters which are sent
back. Since terminals do little or no processing of their own, they are often
called 'dumb' terminals.

In 1982, IBM released the IBM PC microcomputer, which made computing power
affordable to smaller businesses and individuals. Many competitors developed
compatible PCs which were compatible with the MS-DOS operating system used by
the IBM PC (DOS 'clones'). From the outset, PCs used MS-DOS (Microsoft Disk
Operating System), an unsophisticated operating system which allows
application programs (such as word processors, spreadsheets and the like) to
run on PC's. It does not directly support more then one user nor more than one
program at once. MS-DOS continues to be the most used operating system - an
indication of the importance of standards in the computer industry. The early
1980s also saw the release of Apple Computer Inc's Macintosh computer. Like MS-
DOS, the Macintosh operating system was restricted to particular hardware
(the Macintosh) and was single user / single tasking. The main difference was
that the Macintosh operating system incorporated a windowing system and
graphical user interface ('GUI'). GUIs allow users to interact with computers
in a more intuitive fashion. Rather than having to type text based commands,
users manipulate graphical screen elements such as buttons, scroll bars and
dialogue boxes.

The DOS and Macintosh operating systems have been extended in several   [PP20]
ways. In 1989, Microsoft released version 3 of Microsoft Windows, a
windowing system and GUI which sits on top of MS-DOS. It also extends
the basic operating system in several respects, adding (albeit fairly crude)
multi-tasking and support for virtual memory. Around the same time, Apple
released System 7 of the Macintosh operating system, which also added
co-operative multi-tasking and virtual memory. Although DOS/Windows and
Macintosh System 7 have the great majority of the microcomputer market, there
are several contenders, such as IBM's OS/2 and the forthcoming Windows NT from
Microsoft. Both support true pre-emptive multi-tasking, but require faster and
more powerful machines then are commonly found at present.

Mini-computers and mainframes continue to play a role, principally for
centralised database applications and transaction processing systems. Most
previously used proprietary operating systems (such as DEC's VMS, IBM's VM/CMS
and MVS, Data General's AOS and Wang VS), but there has in recent years been a
move towards so-called open systems standardisation on the Unix operating
system. Unix was developed originally (in 1969 at AT&T Bell Labs) as an
interactive multi-tasking development environment for programmers and was not
commercially supported until 1983. One of its major strengths is its
portability to virtually any computer hardware, from mainframes to
microcomputers.


Compatibility of information under different operating systems


Choice of operating systems can have significant implications for
compatibility, both in terms of exchange of data and in the available choice
of software. The Australian organisations involved in criminal trials that
have contributed information for this Report have principally used MS-
DOS/Microsoft Windows and Unix as operating systems, plus a few Macintosh
users. Methods of promoting inter-operability between these operating systems
are available and increasingly powerful. Many programs are now available for
more than one operating system. There are a variety of conversion programs
for converting data between the different data formats used by these operating
systems (as discussed below). There are popular networking approaches for
integrating systems of these three types (also discussed below). Nevertheless,
compatibility questions have to be borne in mind at all times when it is
necessary or desirable to share data or programs with other organisations.
This is particularly so if any operating system other than the standard ones
mentioned above are to be used.


Storage formats and devices


Data can be stored on several different types of devices and in a range of
formats.



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