Module 3 SYSTEM OVERVIEW | Illustrated Unix System V/Bsd

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Module 3
SYSTEM OVERVIEW

DESCRIPTION

This module provides a general overview of UNIX and the UNIX User Utilities described in this book. It specifically covers the following information:

General overview

The UNIX Kernel (the operating system)

Multitasking

Multiuser

Portability

Job control

File System

Directories

Ordinary Files

Special Files

Fifo (pipe)

Device Drivers

The UNIX shell

System Documentation

GENERAL OVERVIEW

The UNIX operating system has rapidly grown in popularity in recent years . Every major computer manufacturer offers a version of UNIX for their hardware, a claim only UNIX can make. It has been ported to over 150 different types of computers, ranging from micros to supercomputers.

The philosophy of UNIX is to modularize problems and build on existing software solutions. Each program should be designed to solve one problem, and complex problems should be solved by combining multiple programs. This basic idea of UNIX is often referred to as the building block approach. Elegantly designed as a simple yet extremely powerful general purpose operating system, UNIX has become a standard in the computer industry.

The UNIX System has introduced many new features to the computer world. Because of its rapid growth in popularity it has become the center of much praise and controversy. It is often referred to as a programmer s dream and a user s nightmare. UNIX is a tremendous solution to many problems, but there are definite weaknesses that are being rectified as new releases are developed. The user interfaces that were once foreign to UNIX are now a reality. There are many software packages available today for UNIX.

THE UNIX KERNEL

The UNIX kernel is the operating system program of UNIX. It is a C and assembly language program that provides the low-level functions of the UNIX environment. It controls the computer hardware and provides an interface for all other UNIX programs to use the hardware. This concept allows the higher level programs to be hardware independent. When a program needs service to a hardware device, it calls on the kernel to perform the function.

The kernel provides the user the ability to interface with the computer hardware and peripherals. When you log in to UNIX you communicate with the kernel via a shell program. Seldom does a user interact directly with the kernel.

MULTITASKING

Multitasking refers to an operating system that executes multiple tasks simultaneously . UNIX refers to a task as a process. UNIX can be configured to allow the user to run from one to as many processes as the operating system can handle. The standard is usually a maximum of 25 processes or tasks per user login. The theory of a multitasking system is to approach 100 percent in computer resource utilization while increasing user productivity. Of course, at some point, one or more resources are over used and productivity begins to fall instead of continuing to rise.

A user can run several commands in background while executing another command in foreground . Background refers to commands that are detached from your terminal. Foreground is the execution of a command attached to your terminal. You must wait for the current foreground command to complete before you can execute another foreground command. Once a command is entered, the system breaks the command down into separate processes if possible. Each process equates to one program or utility. Internal ksh commands do not always generate (spawn) a new process.

MULTIUSER

Multiuser refers to an operating system that allows multiple users to use the system simultaneously. UNIX currently runs on systems that support from one to over 2000 users. The theory of a multiuser system is to approach 100 percent in computer resource utilization while reducing the cost per user. This is done by having multiple users share system resources. A single user cannot use the printer, disk, memory, or cpu 100 percent of the time. But multiple users can increase use of these devices and resources by having an operating system that manages the resources for them. This reduces the cost per user of the computer as more users share the system.

Computers with enough resources to share among multiple users are prime targets for multiuser operating systems. The main requirem2ents are enough RAM memory, disk storage, terminal ports, and cpu power to handle the operating system and each user s computing needs. Even old micros have this capacity ” the popular Intel 80286 or the Motorola 68010 can run 1 to 8 users with relatively good response to each user. The key to good response on UNIX is not just the cpu speed, but a fast access time on your disk drives. The faster your disk drives (low access time) are, the better UNIX responds. It is also very important to have fast I/O to disk and terminal ports.

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