UNIX Unbounded 5th Edition Amir Afzal Chapter 2 The UNIX Operating System Copyright ©2008 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

Chapter 2 The UNIX Operating System This chapter briefly describes the history of the UNIX operating system. It explores UNIX development over the years, discusses the major UNIX versions, and explains some of the system’s important features.

2.1 A BRIEF HISTORY The UNIX operating system was the brainchild of Ken Thompson and Dennis Ritchie Universities and colleges have played an important role in the popularity of the UNIX operating system There are two major versions of the UNIX operating system - AT&T UNIX version V - Berkeley UNIX Other UNIX varieties are based on one of these two versions About 95 percent of the UNIX operating system is written in C. A very small part of UNIX is still written in assembly language; that part is mostly concentrated in the kernel, the part that interacts directly with the hardware.

2.2 Other Unix Systems Linux Solaris UnixWare X Window System X Window system, also referred to as X or X11, is not a UNIX version. It is a graphical user interface designed to provide the bases for graphical windowing in a way that is portable to most UNIX platforms.

2.3: OVERVIEW OF THE UNIX OPERATING SYSTEM The UNIX operating system is implemented in a layered-style software model Kernel The UNIX kernel, also called the base operating system, is the layer that manages all the hardware-dependent functions Resident Modules Layer Provides service routines that perform user-requested service Utility Layer It is the UNIX user interface, commonly referred to as the shell

Figure 2-1: The Unix System Components

2.4 UNIX FEATURES Portability Multiuser capability Multitasking capability Hierarchical File System Device-Independent Input and Output Operations User Interface: Shell Shell Script

Utilities The UNIX system includes more than 100 utility programs, also called commands Utilities are part of the standard UNIX system and are designed to perform a variety of functions required by the users These utilities include the following: • Text editing and text formatting utilities • File manipulation utilities • Electronic mail (e-mail) utilities • Programmers’ tools

System Services The UNIX system provides a number of services that facilitate administration and maintenance of the system. The following are some of these services: • System administration service • System reconfiguration service • File system maintenance service • File transfer service (called UUCP for UNIX to UNIX Copy)