Operating System Concepts
Unit 1
An Operating System (OS) is an interface between a computer user and computer hardware. An
operating system is a software which performs all the basic tasks like file management, memory
management, process management, handling input and output, and controlling peripheral devices
such as disk drives and printers.
Some popular Operating Systems include Linux Operating System, Windows operating System,
VMS, OS/400, AIX, z/OS, etc.
Definition
An operating system is a program that acts as an interface between the user and the computer
hardware and controls the execution of all kinds of programs.
There may be any number of users and any number of applications. The operating system controls
and coordinates the use of the hardware among the various applications programs for the various
users.
Operating System can be defined in many ways based on the function performed by it
1
, 1. It is similar to a “Government” the components of the computer system namely hardware,
software, data etc are manage by the operating system for the successful operation of the computer
system.
2. It provides an environment for specifying certain rules, within which other programs can do
useful work. It can be viewed as “Resource Allocator”. The different resources like CPU time,
memory space, file storage area etc., are managed and allocated to specific program and users are
required. The operating system acts as the manager these resources and allocates them to different
users programs to operate the computer system efficiently and fairly.
3. It is a “Control Program” used to control the various input-output devices and users programs.
A control program controls the execution of user programs to prevent errors and improper use of
the computer.
SOME OF THE MAJOR FACILITIES OF OPERATING SYSTEM
Easy interaction between user and computer
Starting computer operation automatically when power is turned on
Loading and scheduling user programs along with the necessary compilers
Controlling input and output
Controlling program execution
Managing and manipulating files Ex. Editing
Managing and use of main memory
Providing security to users, jobs and files
Resource manager
Helps users to understand the inner functions of computer closely
HISTORY OF OPERATING SYSTEM AND EARLY SYSTEM:
Early computers were very large machines and required purely manual operations to do a task.
The operations required for the execution of programs were, loading the program, loading the
compiler, storing the object program, halting the program on error etc. Here the programmer
himself was the operator. Just to run a very small program, the setup time required was high.
Operating systems were mainly developed to facilitate the use of the hardware and to reduce
the time taken to execute any program. As they were designed and used it became obvious
changes in the design of the hardware could simplify the operating system. As new hardware
were developed special programs to make useof these hardware called “device drivers” were
written. Like this operating system and computer architecture have had a great deal of
influence on each other.
To reduce the set up time involved in the execution of the program batch systems were designed.
A group of similar jobs are submitted at time and the outputs were taken at later stage.
2
, The main disadvantage here was that if any program had stopped due to some error the rest of
the programs could not be run. To overcome this idle CPU time problem “automatic job
sequencing” was introduced. A small program called “Resident Monitor” handles the
transversing of control from one job to another. This is the beginning of OS software. Even with
automatic job sequencing the main CPU often remain idle this was due to the mismatching to
overcome these problems.
Following are some of important functions of an operating System.
Memory Management
Processor Management
Device Management
File Management
Security
Control over system performance
Job accounting
Error detecting aids
Coordination between other software and users
Memory Management
Memory management refers to management of Primary Memory or Main Memory. Main memory
is a large array of words or bytes where each word or byte has its own address.
Main memory provides a fast storage that can be accessed directly by the CPU. For a program to
be executed, it must in the main memory. An Operating System does the following activities for
memory management −
Keeps tracks of primary memory, i.e., what part of it are in use by whom, what part
are not in use.
In multiprogramming, the OS decides which process will get memory when and how
much.
Allocates the memory when a process requests it to do so.
De-allocates the memory when a process no longer needs it or has been terminated.
Processor Management
In multiprogramming environment, the OS decides which process gets the processor when and
for how much time. This function is called process scheduling. An Operating System does the
following activities for processor management −
Keeps tracks of processor and status of process. The program responsible for this task is
known as traffic controller.
Allocates the processor (CPU) to a process.
3
, De-allocates processor when a process is no longer required.
Device Management
An Operating System manages device communication via their respective drivers. It does the
following activities for device management −
Keeps tracks of all devices. Program responsible for this task is known as the I/O
controller.
Decides which process gets the device when and for how much time.
Allocates the device in the efficient way.
De-allocates devices.
File Management
A file system is normally organized into directories for easy navigation and usage. These
directories may contain files and other directions.
An Operating System does the following activities for file management −
Keeps track of information, location, uses, status etc. The collective facilities are often
known as file system.
Decides who gets the resources.
Allocates the resources.
De-allocates the resources.
Other Important Activities
Following are some of the important activities that an Operating System performs −
Security − By means of password and similar other techniques, it prevents unauthorized
access to programs and data.
Control over system performance − Recording delays between request for a service and
response from the system.
Job accounting − Keeping track of time and resources used by various jobs and users.
Error detecting aids − Production of dumps, traces, error messages, and other debugging
and error detecting aids.
Coordination between other softwares and users − Coordination and assignment of
compilers, interpreters, assemblers and other software to the various users of the computer
systems.
Computer-System Organization
A modern general-purpose computer system consists of one or more CPUs and a number of device
controllers connected through a common bus that provides access to shared memory. Each device
4
Unit 1
An Operating System (OS) is an interface between a computer user and computer hardware. An
operating system is a software which performs all the basic tasks like file management, memory
management, process management, handling input and output, and controlling peripheral devices
such as disk drives and printers.
Some popular Operating Systems include Linux Operating System, Windows operating System,
VMS, OS/400, AIX, z/OS, etc.
Definition
An operating system is a program that acts as an interface between the user and the computer
hardware and controls the execution of all kinds of programs.
There may be any number of users and any number of applications. The operating system controls
and coordinates the use of the hardware among the various applications programs for the various
users.
Operating System can be defined in many ways based on the function performed by it
1
, 1. It is similar to a “Government” the components of the computer system namely hardware,
software, data etc are manage by the operating system for the successful operation of the computer
system.
2. It provides an environment for specifying certain rules, within which other programs can do
useful work. It can be viewed as “Resource Allocator”. The different resources like CPU time,
memory space, file storage area etc., are managed and allocated to specific program and users are
required. The operating system acts as the manager these resources and allocates them to different
users programs to operate the computer system efficiently and fairly.
3. It is a “Control Program” used to control the various input-output devices and users programs.
A control program controls the execution of user programs to prevent errors and improper use of
the computer.
SOME OF THE MAJOR FACILITIES OF OPERATING SYSTEM
Easy interaction between user and computer
Starting computer operation automatically when power is turned on
Loading and scheduling user programs along with the necessary compilers
Controlling input and output
Controlling program execution
Managing and manipulating files Ex. Editing
Managing and use of main memory
Providing security to users, jobs and files
Resource manager
Helps users to understand the inner functions of computer closely
HISTORY OF OPERATING SYSTEM AND EARLY SYSTEM:
Early computers were very large machines and required purely manual operations to do a task.
The operations required for the execution of programs were, loading the program, loading the
compiler, storing the object program, halting the program on error etc. Here the programmer
himself was the operator. Just to run a very small program, the setup time required was high.
Operating systems were mainly developed to facilitate the use of the hardware and to reduce
the time taken to execute any program. As they were designed and used it became obvious
changes in the design of the hardware could simplify the operating system. As new hardware
were developed special programs to make useof these hardware called “device drivers” were
written. Like this operating system and computer architecture have had a great deal of
influence on each other.
To reduce the set up time involved in the execution of the program batch systems were designed.
A group of similar jobs are submitted at time and the outputs were taken at later stage.
2
, The main disadvantage here was that if any program had stopped due to some error the rest of
the programs could not be run. To overcome this idle CPU time problem “automatic job
sequencing” was introduced. A small program called “Resident Monitor” handles the
transversing of control from one job to another. This is the beginning of OS software. Even with
automatic job sequencing the main CPU often remain idle this was due to the mismatching to
overcome these problems.
Following are some of important functions of an operating System.
Memory Management
Processor Management
Device Management
File Management
Security
Control over system performance
Job accounting
Error detecting aids
Coordination between other software and users
Memory Management
Memory management refers to management of Primary Memory or Main Memory. Main memory
is a large array of words or bytes where each word or byte has its own address.
Main memory provides a fast storage that can be accessed directly by the CPU. For a program to
be executed, it must in the main memory. An Operating System does the following activities for
memory management −
Keeps tracks of primary memory, i.e., what part of it are in use by whom, what part
are not in use.
In multiprogramming, the OS decides which process will get memory when and how
much.
Allocates the memory when a process requests it to do so.
De-allocates the memory when a process no longer needs it or has been terminated.
Processor Management
In multiprogramming environment, the OS decides which process gets the processor when and
for how much time. This function is called process scheduling. An Operating System does the
following activities for processor management −
Keeps tracks of processor and status of process. The program responsible for this task is
known as traffic controller.
Allocates the processor (CPU) to a process.
3
, De-allocates processor when a process is no longer required.
Device Management
An Operating System manages device communication via their respective drivers. It does the
following activities for device management −
Keeps tracks of all devices. Program responsible for this task is known as the I/O
controller.
Decides which process gets the device when and for how much time.
Allocates the device in the efficient way.
De-allocates devices.
File Management
A file system is normally organized into directories for easy navigation and usage. These
directories may contain files and other directions.
An Operating System does the following activities for file management −
Keeps track of information, location, uses, status etc. The collective facilities are often
known as file system.
Decides who gets the resources.
Allocates the resources.
De-allocates the resources.
Other Important Activities
Following are some of the important activities that an Operating System performs −
Security − By means of password and similar other techniques, it prevents unauthorized
access to programs and data.
Control over system performance − Recording delays between request for a service and
response from the system.
Job accounting − Keeping track of time and resources used by various jobs and users.
Error detecting aids − Production of dumps, traces, error messages, and other debugging
and error detecting aids.
Coordination between other softwares and users − Coordination and assignment of
compilers, interpreters, assemblers and other software to the various users of the computer
systems.
Computer-System Organization
A modern general-purpose computer system consists of one or more CPUs and a number of device
controllers connected through a common bus that provides access to shared memory. Each device
4
