Operating system technical interview questions and answers help students and job seekers understand core computing concepts that are essential for technical interviews. The operating system acts as a bridge between hardware and software, making it one of the fundamental subjects tested in campus placement interviews. Recruiters frequently ask questions about process management, memory allocation, deadlocks, scheduling algorithms, threads, file systems, and OS architecture. These OS interview questions appear repeatedly in companies like TCS, Wipro, Infosys, Cognizant, Capgemini, and Accenture. This guide explains the most commonly asked OS interview questions with easy-to-understand answers, practical examples, and simple definitions. Whether you are preparing for your first job, a technical round, or a written placement test, understanding OS concepts will help you perform confidently. You can also practice mock questions or download PDFs to strengthen your preparation.
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21. Describe the Buddy system of memory allocation.
Free memory is maintained in linked lists, each of equal sized blocks. Any such block is of size 2^k. When some memory is required by a process, the block size of next higher order is chosen, and broken into two. Note that the two such pieces differ in address only in their kth bit. Such pieces are called buddies. When any used block is freed, the OS checks to see if its buddy is also free. If so, it is rejoined, and put into the original free-block linked-list.
22. What is time-stamping?
It is a technique proposed by Lamport, used to order events in a distributed
system without the use of clocks. This scheme is intended to order events consisting of
the transmission of messages. Each system 'i' in the network maintains a counter Ci.
Every time a system transmits a message, it increments its counter by 1 and attaches the
time-stamp Ti to the message. When a message is received, the receiving system 'j' sets
its counter Cj to 1 more than the maximum of its current value and t
23. How are the wait/signal operations for monitor different from those for semaphores?
If a process in a monitor signal and no task is waiting on the condition variable,
the signal is lost. So this allows easier program design. Whereas in semaphores, every
operation affects the value of the semaphore, so the wait and signal operations should be
perfectly balanced in the program.
24. In the context of memory management, what are placement and replacement algorithms?
Placement algorithms determine where in available real-memory to load a
program. Common methods are first-fit, next-fit, best-fit. Replacement algorithms are
used when memory is full, and one process (or part of a process) needs to be swapped out
to accommodate a new program. The replacement algorithm determines which are the partitions to be swapped out.
25. In loading programs into memory, what is the difference between load-time dynamic linking and run-time dynamic linking?
For load-time dynamic linking: Load module to be loaded is read into memory.Any reference to a target external module causes that module to be loaded and the references are updated to a relative address from the start base address of the application module.
With run-time dynamic loading: Some of the linking is postponed until actual reference during execution. Then the correct module is loaded and linked.
26. What are demand- and pre-paging?
With demand paging, a page is brought into memory only when a location on that
page is actually referenced during execution. With pre-paging, pages other than the one
demanded by a page fault are brought in. The selection of such pages is done based on
common access patterns, especially for secondary memory devices.
27. Paging a memory management function, while multiprogramming a processor management function, are the two interdependent?
Yes.
28. What is page cannibalizing?
Page swapping or page replacements are called page cannibalizing.
29. What has triggered the need for multitasking in PCs?
Ø Increased speed and memory capacity of microprocessors together with the support
fir virtual memory and
Ø Growth of client server computing
30. What are the four layers that Windows NT have in order to achieve independence?