UNIX Operating System

Unix started to be developed around 1969, with the first published description appearing in 1973. It was developed at an ATT research lab and was made freely available to universities, encouraging its widespread adoption. Unlike earlier operating systems which had been written in assembly language, the code for Unix was largely in C. The use of a high level language made the code much easier for programmers to understand and maintain. Further, the Unix OS was designed! The programmers who developed Unix started with a clear idea of how their OS was to work and what services it was to provide. Unix was more limited in its aims than many other OSs of the time. It was intended solely to provide a good environment for timeshare style program development. Other OSs were attempting to do timesharing, and database transactions, and run large jobs, but such different uses of a computer tend to conflict resulting in poor performance in all areas. The design for Unix modelled the OS in terms of several layers (when describing the design, someone made an analogy with a nut or an onion and introduced terms like" kernel", "shell" etc - these names have stuck):

• the innermost layer (the "kernel") has the code for the i/o handling routines ("device drivers") etc;

• another layer contains the code for process management, file management, and memory management;

• further layers contain code for looking after wide area and local networks and

so forth;

• the next layer out comprised large numbers of useful utility programs – programs for copying files, comparing files to find differences etc

• the outermost layer (the "shell") was the job control language interpreter, but this JCL interpreter was much more flexible than any that had been proposed

previously.

Unix was originally written for a particular kind of computer (the "PDP11/20") manufactured by Digital Equipment Corporation (DEC). But, the relatively clean design of the system, and the use of a high level language, made it possible for the system to be adapted to other computers (only the "device drivers" and other really low level code had to be redone). Unix was moved to related but more powerful computer architectures (DEC's VAX series of computers) and to totally different computer architectures. During the 1980s, Unix was adapted to run on computers as diverse as the modern Cray supercomputers down to personal computers with Intel-80386 CPU chips. The US Department of Defence's Advanced Research Projects Agency (ARPA) sponsored development of Unix at the University of Berkeley. The Berkeley developers added features to support virtual memory and networking (both wide area and local networking). Late in the 1980s, many computer companies, ATT, Berkeley University, IEEE, etc got together and established standards for all Unix systems.

Unix thus has the advantage of being a system that is non-proprietary, is widely available, and is effective in its original role of supporting program development. Most students continuing with computing studies will eventually get to work with some Unix systems. Modern Unix systems have been expanded so as to handle tasks other than the "programmers' workbench" of the original design. These extensions (to handle large databases, some transaction processing and so forth) were demanded by customers. In some respects, these extensions detract from Unix which no longer has a quite the simplicity and elegance of its early forms.

UNIX. This as, designed by Bell Laboratories for minicomputers and workstations, has been widely adopted by many corporate instal­lations. From the very first, it was designed to be a multi-tasking sys­tem written in C language.

LINUX (Linus Torvalds). Protected under the GNU general pu­blic license Linux is the open source, cooperatively-developed POSIX­ based, multi-tasking operating system. Linux is used as a high-value, fully-functional UNIX workstation for applications ranging from In­ternet Servers to reliable workgroup computing. Linux is available for Intel platforms.

Unit 4

Text Study: Microsoft Operating Systems.

Additional Text: Macintosh OS.

Grammar: Revision of the Module III.