Unix Operating System

Abstract

This paper is a general overview of Unix operating system. It starts by presenting a brief history of the early development of Unix. It concentrates on main aspects of Unix operating system. Key concepts covered are interactive multi-user operating systems, the design objectives of Unix, file-store organization, text processing and programming, the role of C programming language with regard to portability and reliable system software, process control (signals and fork), error logging and recovery from system failures, modifiability and application.

Outline

I. Introduction of Unix

a. History of Unix

b. Interest in Unix

c. Early marketing

d. Developments

i. GUI

ii. Linux

1. Linus Torvalds

II. The Design Objectives of Unix, File-store Organization, Text Processing, and Programming.

a. Benefits of text files

b. Unix shell

c. Unix goals

III. The Role of the C Programming Language with Regard to Portability and Reliable System Software

a. Typeless language

b. Important features of C

IV. Process Control: Signals and Fork

a. State of a process

b. Unix event handling sequence

c. Non-Unix event handling

d. Unix process control allows maximum flexibility

V. Error Logging and Recovery From System Failures

a. Unix recovery features

b. Advantages of recovery procedures

VI. Modifiability and Application Programmer Interface (API).

a. Platform dependency

VII. The User's Perspective on Unix.

VIII. Bibliography

I. Introduction

Strictly speaking, UNIX (in capitals) has been a registered trademark of UNIX System Laboratories (first owned by AT&T, then sold, in 1993, to Novell, Inc., then sold, in 1995, to SCO). The Open Group currently owns the Unix® Trademark. But the word "Unix" has also come to refer to a collection of very closely related operating systems (e.g. AT&T UNIX System V, BSD 4.3 Unix, Sun Microsystems' Solaris, Silicon Graphic's Irix, DEC/Compaq Tru-64 Unix, IBM's AIX, Hewlett-Packard's HP Unix, FreeBSD, NetBSD, SCO UNIX, Minix, Linux, and many others) which have found use on a wide variety of computing platforms, ranging from single-user personal computers to large network server multi-processor machines. Many of these variants are proprietary, but others have source code freely available. For the purposes of this paper, features of the Unix operating system will refer to those features that are common to almost all modern versions of Unix.

It is helpful to give a brief outline of Unix history. UNIX was the creation of a group of researchers at Bell Laboratories (now Lucent Technologies) during the years 1969-1970. The desire was to produce a multi-user, multiprocessing operating system which would support research in computer science, but which had modest hardware requirements (unlike the earlier MULTICS project). Users were expected to connect to the system primarily via terminals over RS-232 serial communication lines. Additional improvements were made over the next few years. The kernel was rewritten in C in 1973. By 1974 Bell Laboratories Version 5 of the UNIX system was available for a nominal charge with full source code and quickly became a popular choice within academic computer science programs.

Interest in UNIX spread overtime and spurred modifications that added functionality. One of the most significant milestones was the addition (in version BSD 4.2 in 1983) of TCP/IP networking via the software abstraction of a network socket. This made it possible for application programmers to write portable code that accessed a network. The mature version of this line of development was BSD 4.3 Unix.

An attempt at consolidation and the adoption of a standard for Unix in the late 1980's produced two camps. One group was formed by the AT&T and Sun Microsystems agreement to merge features of both their systems as System V Release 4 (SVR4). This was marketed by Sun under the Solaris name. A second group (including Apollo Computer, Digital Equipment Corporation, Hewlett-Packard, and IBM) was formed around the Open Software Foundation (OSF) agreement. By this time the line between BSD and System V Unixes had become blurred and the products of both of these groups had features drawn from both parents.

The full Unix operating system had been ported only to the top end of the early personal computer market, since Unix required CPU, memory, and disk resources which were well in excess of what was available on the majority of these early machines. However, the growing popularity of the IBM PC clone as a personal computing platform, and the need to have a system which students could work on encouraged Andrew Tanenbaum to write a small version of Unix in 1986 called Minix, for the PC platform. Although it originally supported multi-processing with a single user and only floppy disk drives for storage, it evolved over the years to Minix 2.0, with many additional features not found in the early versions. The full source code is available. Unlike most Unix operating systems, Minix uses a micro-kernel-based design.

Graphical user interfaces (GUIs) for Unix were available in the early 1980's but all were proprietary and communication at the graphical level between two different Unix platforms was generally not possible. This situation was remedied when the Athena Project at MIT provided a standard platform independent graphical interface for Unix and other operating systems that can be used over a network. It is usually referred to as the X Window System, X11, or simply X. The X Window System has continued to this day to be the main graphical interface for Unix. It was primarily enhanced and distributed commercially by the X Consortium, whose membership included