UNIT-I
Operating Systems Overview:Operating System Functions, Operating System Structure, Operating System
Operations, Protection and Security, Kernel Data Structures, Computing Environments, Open-Source Operating
Systems.
Operating Systems Functions
An operating System (OS) is an intermediary between users and computer hardware. It provides users an
environment in which a user can execute programs conveniently and efficiently.
(or)
In technical terms, It is a software which manages hardware. An operating System controls the allocation of
resources and services such as memory, processors, devices and information.
(or)
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.
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 access directly by the CPU. So for a program to be executed, it
must in the main memory. Operating System does the following activities for memory management.
Department of Computer Science and Engineering: AITS Page 1
, Keeps tracks of primary memory i.e. what part of it are in use by whom, what part are not in
use.
In multiprogramming, OS decides which process will get memory when and how much.
Allocates the memory when the process requests it to do so.
De-allocates the memory when the process no longer needs it or has been terminated.
Processor Management
In multiprogramming environment, OS decides which process gets the processor when and how much time.
This function is called process scheduling. Operating System does the following activities for processor
management.
Keeps tracks of processor and status of process. Program responsible for this task is known as
traffic controller.
Allocates the processor(CPU) to a process.
De-allocates processor when processor is no longer required.
Device Management
OS manages device communication via their respective drivers. Operating System 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. 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 Operating System does.
Security -- By means of password and similar other techniques, preventing 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 software’s and users -- Coordination and assignment of compilers, interpreters,
assemblers and other software to the various users of the computer systems.
Department of Computer Science and Engineering: AITS Page 2
,Operating Systems Objectives/Goals
Convenience
The primary goal of an operating system is convenience for the user. If an application program is a set of
machine instructions then it is completely responsible for controlling the computer hardware. It is a complicated
task. To simplify this task, a set of system programs are provided, called utilities and they implement frequently
used functions which assist in program creation, management of files and control of Input/Output devices.
Efficiency
The secondary goal of an operating system is efficient operation of the system. Operating system is responsible
for managing the resources. That is the movement, storage and processing of data.A portion of operating system
is in main memory. This includes the Kernel or nucleus, which contains the most frequently used functions in
the operating system. The remainder of main memory contains other user programs and data. Operating system
determine how much processor time is to be devoted to the execution of a program. That is the efficient
utilization of the resources.
Ability to Evolve
Operating system should be constructed in such a way as to permit the effective development, testing, and
introduction of new system functions.
Operating system will evolve over time for a number of reasons:
Hardware upgrades plus new types of hardware. For example, view several applications at the
same time through windows.
New services, that is new measurement and control tools may be added.
Fixes, that is faults will be discovered and fixes.
EXTRA-Computer Operating Systems
Operating systems are there from the very first computer generation. Operating systems keep evolving over the
period of time. Following are few of the important types of operating system which are most commonly used.
Serial Processing
Users access the computer in series. From the late 1940's to mid 1950's, the programmer interacted directly
with computer hardware i.e., no operating system. These machines were run with a console consisting of
display lights, toggle switches, some form of input device and a printer. Programs in machine code are loaded
with the input device like card reader. If an error occur the program was halted and the error condition was
indicated by lights. Programmers examine the registers and main memory to determine error. If the program is
success, then output will appear on the printer.
Main problem here is the setup time. That is single program needs to load source program into memory, saving
the compiled (object) program and then loading and linking together .
Batch processing
Batch processing is a technique in which Operating System collects one programs and data together in a batch
before processing starts. Operating system does the following activities related to batch processing.
Department of Computer Science and Engineering: AITS Page 3
, OS defines a job which has predefined sequence of commands, programs and data as a single
unit.
OS keeps a number a jobs in memory and executes them without any manual information.
Jobs are processed in the order of submission i.e first come first served fashion.
When job completes its execution, its memory is released and the output for the job gets copied
into an output spool for later printing or processing.
ADVANTAGES
Batch processing takes much of the work of the operator to the computer.
Increased performance as a new job get started as soon as the previous job finished without any
manual intervention.
DISADVANTAGES
Difficult to debug program.
A job could enter an infinite loop.
Due to lack of protection scheme, one batch job can affect pending jobs.
Operating-System Structure
Multiprogramming
When two or more programs are residing in memory at the same time, then sharing the processor is referred to
the multiprogramming. Multiprogramming assumes a single shared processor. Multiprogramming increases
CPU utilization by organizing jobs so that the CPU always has one to execute.
Following figure shows the memory layout for a multiprogramming system.
Operating system does the following activities related to multiprogramming.
The operating system keeps several jobs in memory at a time.
This set of jobs is a subset of the jobs kept in the job pool.
Department of Computer Science and Engineering: AITS Page 4
Operating Systems Overview:Operating System Functions, Operating System Structure, Operating System
Operations, Protection and Security, Kernel Data Structures, Computing Environments, Open-Source Operating
Systems.
Operating Systems Functions
An operating System (OS) is an intermediary between users and computer hardware. It provides users an
environment in which a user can execute programs conveniently and efficiently.
(or)
In technical terms, It is a software which manages hardware. An operating System controls the allocation of
resources and services such as memory, processors, devices and information.
(or)
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.
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 access directly by the CPU. So for a program to be executed, it
must in the main memory. Operating System does the following activities for memory management.
Department of Computer Science and Engineering: AITS Page 1
, Keeps tracks of primary memory i.e. what part of it are in use by whom, what part are not in
use.
In multiprogramming, OS decides which process will get memory when and how much.
Allocates the memory when the process requests it to do so.
De-allocates the memory when the process no longer needs it or has been terminated.
Processor Management
In multiprogramming environment, OS decides which process gets the processor when and how much time.
This function is called process scheduling. Operating System does the following activities for processor
management.
Keeps tracks of processor and status of process. Program responsible for this task is known as
traffic controller.
Allocates the processor(CPU) to a process.
De-allocates processor when processor is no longer required.
Device Management
OS manages device communication via their respective drivers. Operating System 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. 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 Operating System does.
Security -- By means of password and similar other techniques, preventing 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 software’s and users -- Coordination and assignment of compilers, interpreters,
assemblers and other software to the various users of the computer systems.
Department of Computer Science and Engineering: AITS Page 2
,Operating Systems Objectives/Goals
Convenience
The primary goal of an operating system is convenience for the user. If an application program is a set of
machine instructions then it is completely responsible for controlling the computer hardware. It is a complicated
task. To simplify this task, a set of system programs are provided, called utilities and they implement frequently
used functions which assist in program creation, management of files and control of Input/Output devices.
Efficiency
The secondary goal of an operating system is efficient operation of the system. Operating system is responsible
for managing the resources. That is the movement, storage and processing of data.A portion of operating system
is in main memory. This includes the Kernel or nucleus, which contains the most frequently used functions in
the operating system. The remainder of main memory contains other user programs and data. Operating system
determine how much processor time is to be devoted to the execution of a program. That is the efficient
utilization of the resources.
Ability to Evolve
Operating system should be constructed in such a way as to permit the effective development, testing, and
introduction of new system functions.
Operating system will evolve over time for a number of reasons:
Hardware upgrades plus new types of hardware. For example, view several applications at the
same time through windows.
New services, that is new measurement and control tools may be added.
Fixes, that is faults will be discovered and fixes.
EXTRA-Computer Operating Systems
Operating systems are there from the very first computer generation. Operating systems keep evolving over the
period of time. Following are few of the important types of operating system which are most commonly used.
Serial Processing
Users access the computer in series. From the late 1940's to mid 1950's, the programmer interacted directly
with computer hardware i.e., no operating system. These machines were run with a console consisting of
display lights, toggle switches, some form of input device and a printer. Programs in machine code are loaded
with the input device like card reader. If an error occur the program was halted and the error condition was
indicated by lights. Programmers examine the registers and main memory to determine error. If the program is
success, then output will appear on the printer.
Main problem here is the setup time. That is single program needs to load source program into memory, saving
the compiled (object) program and then loading and linking together .
Batch processing
Batch processing is a technique in which Operating System collects one programs and data together in a batch
before processing starts. Operating system does the following activities related to batch processing.
Department of Computer Science and Engineering: AITS Page 3
, OS defines a job which has predefined sequence of commands, programs and data as a single
unit.
OS keeps a number a jobs in memory and executes them without any manual information.
Jobs are processed in the order of submission i.e first come first served fashion.
When job completes its execution, its memory is released and the output for the job gets copied
into an output spool for later printing or processing.
ADVANTAGES
Batch processing takes much of the work of the operator to the computer.
Increased performance as a new job get started as soon as the previous job finished without any
manual intervention.
DISADVANTAGES
Difficult to debug program.
A job could enter an infinite loop.
Due to lack of protection scheme, one batch job can affect pending jobs.
Operating-System Structure
Multiprogramming
When two or more programs are residing in memory at the same time, then sharing the processor is referred to
the multiprogramming. Multiprogramming assumes a single shared processor. Multiprogramming increases
CPU utilization by organizing jobs so that the CPU always has one to execute.
Following figure shows the memory layout for a multiprogramming system.
Operating system does the following activities related to multiprogramming.
The operating system keeps several jobs in memory at a time.
This set of jobs is a subset of the jobs kept in the job pool.
Department of Computer Science and Engineering: AITS Page 4
