Ex. No: 1 Study of OPERATING SYSTEM
Date:
Definition of Operating System
An operating system (OS) is a software program designed to act as an interface between the user and the computer. It controls the computer hardware, manages the system resources, and supervises the interaction between the system and the user. The operating system also forms a database on which application software is developed and executed.
Function of an operating system
Command interpretation: The CPU can’t understand the commands keyed in by a user. It is the function of the OS to make it understand.
Peripheral Interfaces: the OS also has to take care of the devices attached to the
system. The OS oversees communication between these devices and the CPU.
Memory management: the OS handles the extremely important job of allocating
memory for various processes running on the system.
Process management: this is required if several programs must run concurrently. CPU
time would then have to be Rationed out by the OS to ensure that no programs gets
more than its fair share of the processor time.
Types of operating system
There are two basic types of operating system – single-user and multi-user. A multi-user operating system handles multiple users as well as multiple peripheral devices simultaneously. Such an operating system is more than single-user OS.
Single user systems:A personal computer is a popular single user system. The PC is a small general-purpose system that can execute programs to perform a wide verity of tasks.
Multi-user system are required when a number of program have to be run simultaneously, or common resources like printers and disks are to be shared by a number of users.
Basic concepts of multi-user system
A multi-user system has a single computer with several terminals attached to it. This computer can be a PC – AT, a mini or a mainframe. Various users can work on this machine through the attached terminals. These terminals can be of two types: Smart & Dumb.
A Dumb terminal consists of a VDU and a keyboard. It has no CPU of it’s own, and the processes is done only by the central unit.
A Smart terminal has it’s own CPU and peripherals, and can work independent of the central unit.
UNIX Kernel
The core of the UNIX system is the kernel – the operating system program. The kernel controls the computer resources, allocating them to different users and different tasks. It interacts directly with the hardware. Since the kernel communicates with the hardware, parts of the kernel must be customized to each systems hardware features. However the kernel doesn’t deal directly with the user instead it stars up a separate interactive program called the shell for each user
UNIX utilities
Unix utilities or commands are a collection of about two hundred programs that service the day to day processing requirements. This programs are invoked through shell which itself an utility.
Application software
Apart from the utilities that are provided as a part of the UNIX operating system more than a thousand UNIX based application programs like database management systems, word processor, accounting software, and language processor are available from independent software vendors.
UNIX file system
A single fixed disk can store thousands of files for organizing data in the disk; the operating system provides a file system. This file system allows you to group files in a convenient manner.
When UNIX was developed it had features that the other operating system at that time did not have. Once such feature was it file system. The UNIX file system has a hierarchical structure and the files can be stored at the directories. Directories are similar to the drawers of the filling cabinet. Just as each drawer contains the files, each of which contains the files of the similar nature. Additionally, just as in a filling cabinet, the user decides the drawer labels and contents, so also the user decides the directory name and the files in the directory. All the files are stored on the disk under one main directory for the root directory.
File naming conventions :
In UNIX file, filenames
Can be up to 14 char long.
Can contain digits, a dot (.), hyphen (-) are the underscore symbol (_) anywhere.
Can contain both upper case and lower case alphabets.
Are case sensitive.
For example:
THIS_FILE is not same as this_file.
a.h is not the same as A.H or A.h.
Should not have a blank or a tag.
Starting a UNIX session – Logging In :
A user of Unix based system works as a user terminal. After the boot procedure is completed, that is the operating system is loaded in memory, the following message appears at each user terminal:
Logging:
Each user has a identification called the user name are the login name which has to be entered when the login: message appears. The user is then asked to enter the password. Unix keeps track of all the Unix user names and the information about identity in a special file. If the login name entered does not match with any of the user names it displays the login message again. This ensures that, only authorized people use the system. When a valid user name is entered at the terminal the dollar symbol is displayed on the screen this is the Unix prompt.
Ending a UNIX session –Logging Out:
Once a user has logged into the system the users works session continues until the user instructs the shell to terminate the session. This is done by pressing the ctrl and ‘d keys’ together or typing exit at the dollar prompt. Then the system display the login: Prompt on the screen.