From the fastest supercomputer and largest mainframe, right down to the smallest embedded microprocessor in a microwave oven or watch, every computer uses an operating system. Over the years, a variety of operating systems have been developed and many remain in use. When the IBM PC set the standard for microcomputers, DOS (Disk Operating System) become the most widely used microcomputer operating. Today, DOS has been replaced by more powerful operating systems such as Windows, UNIX, Windows NT, Linux and OS/2 etc. These operating systems make it possible to run tasks on less expensive microcomputers that were once performed on expensive mainframes and minicomputers.

Microsoft Disk Operating System (MS DOS):

MS-DOS, developed by Microsoft Corporation, became the defector standard for machines designed with Intel microprocessors. MS-DOS was selected by IBM for its PCs. This established the popularity of MS-DOS. Since IBM hardware and its compatibles hold a large share of the microcomputer market, application software became abundant for MS-DOS. The IBM version of MS-DOS is known as PC-DOS.

DOS is helpful to organize disks and use them efficiently. It helps to create and manage files on disks, make copies of them or remove unwanted files from the disks.

MS-DOS 5.0 comes equipped with a graphical user interface (GUI) called the DOS Shell. This interface helps the user with everyday tasks such as starting a program or formatting a floppy disk. With the GUI the desired task can be easily selected and started with the mouse, by just pointing to the item on the screen and clicking the mouse button.

The DOS shell also provides an overview of the contents of the hard disk and floppy disk any time. Several programs can be started at once but only one program runs at a time, the others are suspended.

Because DOS was developed for early 16-bit processors, it cannot task full advantage for advanced capabilities of Intel 32-bit or higher microprocessors. However, use of DOS is declining rapidly.

Mac Operating System (Mac OS):

Mac Os introduced the graphical user interface bringing the UNIX idea to microcomputer. The original Mac OS released in 1984, consisted of System and Finder. By late 1980s, the Mac’s operating system was the most technologically advanced n personal computing, but Apple computer was unable to capitalize on its lead, and Mac OS fell behind Microsoft Window. Mac OS is widely considered to be easiest operation system for computer users. Mac Os released an improved version in 1988, which is up to the standard of Microsoft Windows 98.

Windows 3.XX:

Microsoft Windows 3.XX is an extension to the DOS operating system and cannot run without DOS. It is a graphical user interface whose features extend far beyond those of the DOS Shell. Although it was designed for 32-bit, full advantage of it is limited as it has to run in cooperation of DOS.

Microsoft released Windows in 1984. The goal of this graphical user interface is to make the computer friendlier to the users. With Windows, applications files are presented as symbols (icons) on the screen. Simply pressing a key or clicking the mouse activates a command. Owing to the success of Windows, Windows-compatible application software becomes very popular. Also Windows accessory programs are available to accomplish many tasks within Windows itself. Windows permits multitasking whereby several programs can be run at once. However, it uses cooperative multitasking, which means that the failure of any one application in likely to crash the whole system

Microsoft Windows 95, 98 and 2000:

Microsoft Windows 95 is an operating system which fully supports 32-bit processing capabilities. It also supports preemptive multitasking, which enables the operating system to regain control if an application crashes.

Windows 95, or Win 95, is an operating system, poised between Windows 3.XX (a 16-bit operating system) and Windows NT (32-bit with advanced features). Win 95 is designed to run many existing 16-bit applications designed for windows 3.XX as well as new 32-bit applications.

Microsoft Windows 98, or Win 98 (released in 1988), is an improved version of Win 98 that offers

• Better stability
• Improved Internet connectivity
• Drivers for new peripherals

A new version of Windows called Windows 2000 is available with a lot of additional facilities which include networking applications.

Microsoft Windows 95, 98 and 2000

Microsoft windows CE:

Microsoft windows CE is simplified version of Windows, designed for palmtop computer. Windows CE includes an interactive scheduling calendar, an address book for contacts, electronic mail, and web browsing. By means of an automatic active synchronization program, users can quickly synchronize the corresponding utilities on their computers; Windows CE includes handwriting recognition and support for voice recording as well.

Microsoft Windows NT:

Microsoft Windows NT (New Technology) is a 32-bit operating system, specifically designed for client/server system, formerly a strong hold of UNIX. It has two components to support namely, client and server.

Windows NT Workstation for desktop computers is similar to but more powerful than Win 98. IT is faster than Win 98 and supports network environment. Windows NT desktops can be linked to servers running Windows NT server. Windows NT server offers

• Strong security to network recourses
• Rmote network administration
• Web server scope to make Web pages available
• Directory services to map files and applications available on the network

UNIX:

It is a multi-user operating system for powerful 16-bit and 32-bit machines. UNIX set the standard for multi-user systems for personal computers. Developed at AT&T’s Bell Laboratories in USA, UNIX held monopoly in the multi-user OS market for quite some time before other operating systems were introduced. It was first written in the assembly language. Later in 1973, it was rewritten in C language. This gives it portability i.e., it could be run easily on different types of machines. This is one important reason for the popularity of UNIX. There are several implementations of this system. The greatest success of UNIX lies in client/server computing, a type of computer usage that is widely found in corporations today. UNIX also provides

• Highest level of security for applications and access control and
• Faster services

Linux:

Linux a new flavor of UNIX operating system is the fastest growing operating system for Intel based personal computers. Two important characteristics make Linux attractive. These are:

• It is powerful
• It is free

Linux brings all the maturity and sophistication of UNIX to the PC, including multitasking, virtual memory, internet support, multiprocessor support and graphical user interface.

Linux is distributed with General Public License. In practice, most people buy a Linux distribution, a CD-ROM containing Linux and a collection of drivers, utilities, GUI interfaces and application programs.

Linux, a derivation of UNIX, is a freeware operating system. However, Linux cannot run most popular Microsoft Office applications. Linux is gaining increasing acceptance for web and other applications.

Xerox PARC:

Xerox PARC (Palo Alto Research Center) was the first GUI (Graphical User Interface) operating system developed in 1970. Xerox PARC originated the idea of desktop icon, on screen fonts, windows and pull-down windows. Although Xerox released a GUI based computer in 1981, the company was never able to capitalize on its innovations.