1. What is an Operating System?
An operating system is a program that manages the
computer hardware. It also provides a basis for application programs and act as
an intermediary between a user of a computer and the computer hardware. It
controls and coordinates the use of the hardware among the various application
programs for the various users.
2. Why is the Operating System viewed as a
resource allocator & control program?
A computer system has many
resources – hardware & software that may be required
to solve a problem, like CPU time, memory space, file-storage space, I/O
devices & so on. The OS acts as a manager for these resources so it is
viewed as a resource allocator. The OS is viewed as a control program because
it manages the execution of user programs to prevent errors & improper use
of the computer.
3. What is the Kernel?
A more common definition is that the
OS is the one program running at all times on the computer, usually called the
kernel, with all else being application programs.
4. What are Batch Systems?
Batch systems are quite
appropriate for executing large jobs that need little interaction. The user can
submit jobs and return later for the results. It is not necessary to wait while
the job is processed. Operators batched together jobs with similar needs and
ran them through the computer as a group.
5. What is the advantage of Multiprogramming?
Multiprogramming increases CPU
utilization by organizing jobs so that the CPU always has one to execute.
Several jobs are placed in the main memory and the processor is switched from
job to job as needed to keep several jobs advancing while keeping the peripheral
devices in use. Multiprogramming is the first instance where the Operating
system must make decisions for the users. Therefore they are fairly
6. What is an Interactive Computer System?
Interactive computer system
provides direct communication between the user and the system. The user gives
instructions to the operating system or to a program directly, using a keyboard
or mouse, and waits for immediate results.
7.What do you mean by Time-Sharing Systems?
Time-sharing or multitasking is a
logical extension of multiprogramming. It allows many users to share the
computer simultaneously. The CPU executes multiple jobs by switching among
them, but the switches occur so frequently that the users can interact with
each program while it is running.
8.What are Multiprocessor Systems & give their
Multiprocessor systems also known
as parallel systems or tightly coupled systems are systems that have more than
one processor in close communication, sharing the computer bus, the clock and
sometimes memory & peripheral devices. Their main advantages are,
9.What are the different types of Multiprocessing?
multiprocessing (SMP): In SMP each processor runs an identical copy
of the OS
& these copies
communicate with one another as needed.
All processors are peers.
are Windows NT, Solaris, Digital UNIX, and OS/2 & Linux.
Asymmetric multiprocessing: Each
processor is assigned a specific task. A master processor
controls the system; the other processors look to the master for instructions
or predefined tasks. It defines a master-slave relationship.
SunOS Version 4.
10. What is Graceful Degradation?
In multiprocessor systems,
failure of one processor will not halt the system, but only slow it down. If
there is ten processors & if any one fails then the remaining nine
processors pick up the work of the failed processor. This ability to continue
providing service is proportional to the surviving hardware is called graceful
11. What is Dual- Mode Operation?
The dual mode operation provides
us with the means for protecting the operating system from wrong users and
wrong users from one another. User mode and monitor mode are the two modes.
Monitor mode is also called supervisor mode, system mode or privileged mode.
Mode bit is attached to the hardware of the computer in order to indicate the
current mode. Mode bit is ‘0’ for monitor mode and ‘1’ for user
12. What are Privileged Instructions?
Some of the machine instructions that may cause harm to a
system are designated as privileged instructions. The hardware allows the
privileged instructions to be executed only in monitor mode.
How can a user program disrupt the normal operations
of a system?
A user program may disrupt the normal operation of a system
illegal I/O operations
accessing memory locations within the OS itself
to relinquish the CPU
How is the protection for memory provided?
The protection against illegal
memory access is done by using two registers. The base register and the limit
register. The base register holds the smallest legal physical address; the
limit register contains the size of the range. The base and limit registers can
be loaded only by the OS using special privileged instructions
15. What are the various OS Components?
The various system components
are, Process management
Main memory management
Secondary storage management
Commnd interpreter system
16. What is a Process?
A process is a program in
execution. It is the unit of work in a modern operating system. A process is an
active entity with a program counter specifying the next instructions to
execute and a set of associated resources. It also includes the process stack,
containing temporary data and a data section containing global variables.
17. What is a Process State and mention the
various States of a Process?
As a process executes, it changes
state. The state of a process is defined in part by the current activity of
Each process may be in one of the following states:
18. What is Process Control Block (PCB)?
Each process is represented in the operating system by a
process control block also called a task control block. It contains many pieces
of information associated with a specific process. It simply acts as a
repository for any information that may vary from process to process. It
contains the following information:
CPU scheduling information
Memory management information
I/O status information
19. What is the use of Job Queues, Ready Queues
& Device Queues?
As a process enters a system,
they are put into a job queue. This queue consists of all jobs in the system.
The processes that are residing in main memory and are ready & waiting to
execute are kept on a list called ready queue. The list of processes waiting
for a particular I/O device is kept in the device queue.
20. What is meant by Context Switch?
Switching the CPU to another
process requires saving the state of the old process and loading the saved
state for the new process. This task is known as context switch. The context of
a process is represented in the PCB of a process.
21. What is Spooling?
Spooling means Simultaneous
Peripheral Operations On Line. It is a high-speed device like a disk is
interposed between a running program and a low –speed device
involved with the program in input/output. It disassociates a running program
from the slow operation of devices like printers.
22. What are System Calls?
System calls provide the interface between a process and the
Operating system. System Calls are also called as Monitor call or
Operating-system function call. When a system call is executed, it is treated
as by the hardware as software interrupt. Control passes through the interrupt
vector to a service routine in the operating system, and the mode bit is set to
23. List the services provided by an Operating
File System manipulation
24. What are the two types of Real Time System?
Hard real time system
Sot real time system
A hard real time system
guarantees that critical tasks complete on time. In a soft real time system, a
critical real-time task gets priority over the other tasks, and retains that
priority until it completes. Soft real time systems have more limited utility
than do hard real-time systems.
26. Write the difference between Multiprogramming
and Non - Multiprogramming?
The operating system picks and
begins to execute one of the jobs in the memory. Eventually, the job may have
to wait for some task, such as a tape to be mounted, or an I/O operation to
complete. In a non-multiprogrammed system, the CPU would sit idle. In a
multiprogramming system, the operating system simply switches to and executes
When that job needs to wait, the
CPU is switched to another job, and so on. Eventually, the first job finishes
waiting and gets the CPU back. As long as there is always some job to execute,
the CPU will never be idle.
27. What are the design goals of an Operating
The requirements can be divided
into two basic groups: User goals and System goals.Users desire that the system
should be convenient and easy to use, easy to learn, reliable, safe and fast.
The Operating system should be easy to design, implement, and maintain. Also it
should be flexible, reliable, error free and efficient. These are some of the
requirements, which are vague and have no general solution.
28. What are the five major categories of System
29. What is the use of Fork and Execve System
Fork is a System calls by which a new process is
created. Execve is also a System call, which is used after a fork by one of the
two processes to replace the process memory space with a new program.
30. Define Elapsed CPU time and Maximum CPU time?
Elapsed CPU Time: Total CPU
time used by a process to date.
CPU Time: Maximum amount of CPU time a process may use.