Operating System

1)What is an operating system?
Ans: It is a program that acts as intermediary between computer user and computer hardware and provides basis for application programs.

2)What operating systems do?
Ans:It controls and coordinates the use of hardware among various application programs .

3)Why operating system is regarded as resource allocator ?
Ans:The operating system acts as the manager of different resources of computer such as CPU time,memory space,file storage space,I/O devices etc. The operating system decides how to allocate resources to specific program and users for efficient working of computer system.

4)What is a control program?
Ans:Control program manages the execution of user programs to prevent errors and improper use of computer.

4)What is a bootstrap program?
Ans:The intial program needed by computer to start running when computer is rebooted or powered on is called boot strap program.It is stored in ROM or EEPROM (firmware).
It initializes all aspects of system from cpu registers to device controllers to memory contents.

5)Discuss computer system operation?
Ans:
->Run bootstrap program.
->Bootstrap program load and locate into memory the operating system kernel.
->O.S execute first process such as init and wait for some event to occur.
->Occurrence of event is signaled by interrupt from h/w(system bus sending signal to CPU) or s/w(system or monitor call).
->When cpu is interrupted , it stops what it is doing and transfers execution to fixed location.
->Fixed location contains starting address where service routine for interrupt is located.
->Execution of interrupt service routine.
->CPU resumes interrupted computation after completing interrupt service routine.

6)How multiprogramming increases CPU utilization?
Ans: Multiprogramming increase CPU utilization by organizing jobs :
->O.S keeps several jobs in memory.
->It is a subset of job pool(total number of jobs that enter the system).
->O.S picks and begins to execute one of the job in memory.
->Eventually job has to wait for some time till resource is unavailable.
->Thus CPU never remains idle as it always has one or other job to do.

7)What is difference between multiprogramming and Time Sharing?
Ans:Time sharing is logical extension of multiprogramming.In time sharing ,users can interact with each program as switching between the jobs take place frequently whereas in case of multiprogramming there is no user interaction with the computer system.

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