Sunday, 24 July 2016

Best 30 Operating Systems Interview Question Answers-Part 1

1. What are the basic functions of an operating system?

Operating system controls and coordinates the use of the hardware among the various
applications programs for various uses. Operating system acts as resource allocator and manager.
Since there are many possibly conflicting requests for resources the operating system must
decide which requests are allocated resources to operating the computer system efficiently and
fairly. Also operating system is control program which controls the user programs to prevent
errors and improper use of the computer. It is especially concerned with the operation and
control of I/O devices.
2. Why paging is used?
Paging is solution to external fragmentation problem which is to permit the logical address space
of a process to be noncontiguous, thus allowing a process to be allocating physical memory
wherever the latter is available.
3. While running DOS on a PC, which command would be used to duplicate the
entire diskette?
4. What resources are used when a thread created? How do they differ from those
when a process is created?
When a thread is created the threads does not require any new resources to execute the thread
shares the resources like memory of the process to which they belong to. The benefit of code
sharing is that it allows an application to have several different threads of activity all within the
same address space. Whereas if a new process creation is very heavyweight because it always
requires new address space to be created and even if they share the memory then the inter
process communication is expensive when compared to the communication between the threads.
5. What is virtual memory?Virtual memory is hardware technique where the system appears to have more memory that it
actually does. This is done by time-sharing, the physical memory and storage parts of the
memory one disk when they are not actively being used.
6. What is Throughput, Turnaround time, waiting time and Response time?
Throughput  number of processes that complete their execution per time unit.
Turnaround time amount of time to execute a particular process. Waiting time
 amount of time a process has been waiting in the ready queue. Response time
 amount of time it takes from when a request was submitted until the first
response is produced, not output (for time-sharing environment).
7. What is the state of the processor, when a process is waiting for some event to occur?
 Waiting state
8. What is the important aspect of a real-time system or Mission Critical Systems?A real time operating system has well defined fixed time constraints. Process must be done
within the defined constraints or the system will fail. An example is the operating system for a
flight control computer or an advanced jet airplane. Often used as a control device in a dedicated
application such as controlling scientific experiments, medical imaging systems, industrial
control systems, and some display systems. Real-Time systems may be either hard or soft realtime.
Hard real-time: Secondary storage limited or absent, data stored in short term memory, or
read-only memory (ROM), Conflicts with time-sharing systems, not supported by generalpurpose
operating systems. Soft real-time: Limited utility in industrial control of robotics, Useful
in applications (multimedia, virtual reality) requiring advanced operating-system features.
9. What is the difference between Hard and Soft real-time systems?A hard real-time system guarantees that critical tasks complete on time. This goal requires that
all delays in the system be bounded from the retrieval of the stored data to the time that it takes
the operating system to finish any request made of it. A soft real time system where a critical
real-time task gets priority over other tasks and retains that priority until it completes. As in hard
real time systems kernel delays need to be bounded
10. What is the cause of thrashing? How does the system detect thrashing? Once itdetects thrashing, what can the system do to eliminate this problem?
Thrashing is caused by under allocation of the minimum number of pages required by a process,
forcing it to continuously page fault. The system can detect thrashing by evaluating the level of
CPU utilization as compared to the level of multiprogramming. It can be eliminated by reducing
the level of multiprogramming.

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