Unix Primer:Motivation and Unix Environment.

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Module 10: Unix Primer

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From UNICS To Unix: A brief history: - Early on, in the 1960s and 1970s, every major computer manufacturer supplied operating system as a proprietary software.

Such OSs were written specifically for their own machine. In particular, each machine had an instruction set and the operating system was generally written in its intermediate language (often assembly language). As a result, no two operating systems were alike in features. When a user moved to a new machine, he would be expected to learn the new operating system. No two machines could even exchange information, not to mention the notion of portability of software.

It was in this context, that “unics", an acronym for uniplexed information and computing system was developed by Dennis Richie at Bell Laboratories in USA. The idea was to offer an interpreted common (uniplexed) command language environment across platforms. Unics later became UNIX [16].

To implement this idea, Bell Laboratory team developed the idea of isolating a basic “kernel" and a “shell". Most OSs today follow UNIX design philosophy of providing a kernel and a shell. Modern Unix-based environments support an extensive suite of tools.

10.1 Motivation

Unix is a popular operating system. Unix philosophy has been to provide a rich set of generic tools and to support tool based application development. For instance, Unix provides generic string matching tools which are very useful in software development. These tools and utilities also aid in enhancing a user's productivity. Clearly, the main advantage of such an approach is to leave a lot of leeway for the users. Experience indicates that this encourages users to use tools in innovative ways to create new applications. Or they may just create a pleasant customised work environment. Now contrast this with a closed and/or packaged environment. That leaves little room, if any, for creative composition or enhancements. It offers little or no outlet to a user to customise the working environment. In Unix, users have access to the same tools which are also used by Unix as an OS. This gives one a peek into the working of the internals of Unix as well. In fact, by letting the user enrich the tool suite, or the OS utilities, Unix users expand their horizon. This is what makes Unix an open system.

Besides the tools and utilities orientation, there were two other major developments which have affected operational environments. First, the development of X-windows offered users a very helpful environment to develop graphical user interface (GUI) for newer applications. Secondly, Unix provided a strong backbone support in the development of computer communication networks by supporting client-server architecture. In fact, the TCP/IP suite of protocols (which forms the core of internet operations) was first developed on Unix.

In this module we shall study the elements of the Unix operating systems.

10.2 Unix Environment

Unix, with X-windows support, provides a virtual terminal in every window. A Unix environment is basically a command driven environment1. Each window can be used to give commands. With this a user can run multiple applications, one in each of the windows. A user may open more windows if he needs them (though there is usually an upper limit to the number of windows that may be active at one time).

Basically Unix provides a user a friendly shell. It hides the system kernel beneath the shell. The shell interface accepts user commands. The user command is interpreted by the shell and then the shell seeks the desired service from the kernel on behalf of the user.

In Unix everything veers around the following two basic concepts:

• Files

• Processes

Users organise applications using files and processes. A program text is a file. A program in execution is a process.

An application may be spread over several files. In addition to program files, there may be other kinds of data files too. Files are generated with some end application in mind. For instance, a file may be a text file for document generation or it may be an image file supporting some medical information in a health-care system. A user may have many applications. Each application may require several files. Unix file system helps users in organizing their files. Next we shall study the file system in Unix.

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