Operating system notes
Introduction to computer system
A computer system consists of hardware, system programs and various application programs.
(fig: Computer system)
Computer system have a capability for gathering data, performing computations, storing information, communicating with other computer systems and generating output. The hardware (the central processing unit, the memory and the input-output devices) provides the basic computing resources for system. The application programs such as word processing, compilers and assemblers defines the way in which these resources and co-ordinates the use of the hardware among the various application programs for the various system users. The operating system provides the means for proper use of these resources in the operation of the computer system.
Definition of operating system:
An operating system is an organized collection of system program that control overall operation of computer system. Basically, an OS is a computer program (mainly system software) that takes part as an inter-mediator between the user and the computer hardware.
Goals of operating system
-->Execute user programs and make solving user problems easier.
-->Make the computer system convenient to use
-->Use the computer hardware in an efficient manner.
Thus OS provides an environment within which other programs can do useful works.
An operating system can be broadly defined as:
-->Operating system as an Extended Machines
-->Operating system as a Resource Manager
-->Operating system is a control program
Operating system as an Extended Machine
The function of the operating system is to present the user with the equivalent of an extended machines or virtual machines that is easier to program than the underlying hardware. For this OS creates high-level abstraction for programmer. To understand this we take the example of floppy disk I/O operation:
--> Disk contains a collection of named files.
--> Each file can be open for READ/WRITE.
--> After READ/WRITE completes close that file.
--> No any detail to deal
So, OS shields the programmer form the disk hardware and presents a sample file oriented interface.
--> Hides the messy details which must be performed.
--> Presents user with a virtual machine, easier to use
-->A standardized "Visual Machine" across different physical machines.
-->Allows easy program distribution
Operating System as a Resource Manager:
A modern computer consists of processors, memories, timers, disks, mice, network interfaces, printers and wide variety of other devices. The job of OS is to provide for an oderly and controlled allocation of the processors, memories, and I/O devices among various programs. Resource management includes sharing resources in 2 ways. Time and space. When a resource is time multiplexing, different programs or users take turns using it. The other type of multiplexing is space multiplexing. Instead of the customer taking turns, each one get part of the resource.
OS is a control Program
-->Controls execution of programs to stop errors and unmanaged use of the computer.
OS can be seen from 2 view pointes
a) Resource managers :- OS's job is to effictively and efficiently manage different parts of system.
b)Extended machine :- The job of system is to provide the users with a virtual machine which is more convenient than actual machine.
Measuring the system performance
System performance can be carried out by following parameters:
a) Throughput
b) Turnaround Time:
c) Response time:
a) Throughput:- It is the amount of work that a system is able to do per unit time. It determines the no
of jobs or process completed by the system per unit time.
For eg:
If system complete n job or process in t time then,
throughput is n/t.
b)Turnaround Time:-
Tags: operating system notes goal of operating system Operating system as an Extended Machine Operating System as a Resource Manager Measuring the system performance throughput turnaround time response time
A computer system consists of hardware, system programs and various application programs.
(fig: Computer system)
Computer system have a capability for gathering data, performing computations, storing information, communicating with other computer systems and generating output. The hardware (the central processing unit, the memory and the input-output devices) provides the basic computing resources for system. The application programs such as word processing, compilers and assemblers defines the way in which these resources and co-ordinates the use of the hardware among the various application programs for the various system users. The operating system provides the means for proper use of these resources in the operation of the computer system.
Definition of operating system:
An operating system is an organized collection of system program that control overall operation of computer system. Basically, an OS is a computer program (mainly system software) that takes part as an inter-mediator between the user and the computer hardware.
Goals of operating system
-->Execute user programs and make solving user problems easier.
-->Make the computer system convenient to use
-->Use the computer hardware in an efficient manner.
Thus OS provides an environment within which other programs can do useful works.
An operating system can be broadly defined as:
-->Operating system as an Extended Machines
-->Operating system as a Resource Manager
-->Operating system is a control program
Operating system as an Extended Machine
The function of the operating system is to present the user with the equivalent of an extended machines or virtual machines that is easier to program than the underlying hardware. For this OS creates high-level abstraction for programmer. To understand this we take the example of floppy disk I/O operation:
--> Disk contains a collection of named files.
--> Each file can be open for READ/WRITE.
--> After READ/WRITE completes close that file.
--> No any detail to deal
So, OS shields the programmer form the disk hardware and presents a sample file oriented interface.
--> Hides the messy details which must be performed.
--> Presents user with a virtual machine, easier to use
-->A standardized "Visual Machine" across different physical machines.
-->Allows easy program distribution
Operating System as a Resource Manager:
A modern computer consists of processors, memories, timers, disks, mice, network interfaces, printers and wide variety of other devices. The job of OS is to provide for an oderly and controlled allocation of the processors, memories, and I/O devices among various programs. Resource management includes sharing resources in 2 ways. Time and space. When a resource is time multiplexing, different programs or users take turns using it. The other type of multiplexing is space multiplexing. Instead of the customer taking turns, each one get part of the resource.
OS is a control Program
-->Controls execution of programs to stop errors and unmanaged use of the computer.
OS can be seen from 2 view pointes
a) Resource managers :- OS's job is to effictively and efficiently manage different parts of system.
b)Extended machine :- The job of system is to provide the users with a virtual machine which is more convenient than actual machine.
Measuring the system performance
System performance can be carried out by following parameters:
a) Throughput
b) Turnaround Time:
c) Response time:
a) Throughput:- It is the amount of work that a system is able to do per unit time. It determines the no
of jobs or process completed by the system per unit time.
For eg:
If system complete n job or process in t time then,
throughput is n/t.
b)Turnaround Time:-
Turnaround time is the interval between the time of submission of a job
to the system for processing
to the time
of
completion of the job.
c) Response Time:-
c) Response Time:-
Turnaround time is not a suitable for interactive systems because in such a system a process can produce some
output early during its execution and can continue executing
white previous results are being output to the user. Hence, another measure used m
case of interactive system is
response time. It is the interval between the times of submission of a job of the system for processing time of the system
producing the first response for the job. In any computer system, it is desirable to maximize throughput and minimize
turnaround and response time.
Tags: operating system notes goal of operating system Operating system as an Extended Machine Operating System as a Resource Manager Measuring the system performance throughput turnaround time response time
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