OPERATING SYSTEMS
2 MARKS --UNIT 1
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.
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 eachprogram while it is running.
8. What are multiprocessor systems & give their advantages?
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
Increased throughput
Economy of scale
Increased reliability
9. What are the different types of multiprocessing?
Symmetric 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. Examples are Windows NT, Solaris, Digital
UNIX, 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. Example 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 are ten processors & if one fails 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 degradation.
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 to indicate the current mode. Mode bit is ‘0’ for
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.
13. How can a user program disrupt the normal operations of a system?
A user program may disrupt the normal operation of a system by
Issuing illegal I/O operations
By accessing memory locations within the OS itself
Refusing to relinquish the CPU
14. 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
File management
I/O-system management
Secondary-storage management
Networking
Protection system
Command-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 that process. Each process may be in
one of the following states:
New
Running
Waiting
Ready
Terminated
18. What is process control block?
Each process is represented in the operating system by a process
It contains the following information:
Process state
Program counter
CPU registers
CPU-scheduling information
Memory-management information
Accounting information
I/O status information
19. What are 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 calledready 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.
