ABHYAS PREP: COMPUTER SCIENCE MCQS · OPERATING SYSTEM CONCEPTS

Operating System Concepts

Processes, scheduling, deadlocks, memory and paging.

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Worked examples

Example 1 · level 1

Two threads belonging to the same process in a Linux-based system will share which of the following?

Address space and open files
Stack and program counter
Register set and local variables
Each thread has its own heap

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Identify that threads are lightweight units of a process.
Recall that shared resources include code, data, and OS resources.
Recall that private resources include stack and registers.

Answer: Address space and open files

Example 2 · level 2

A system uses 32-bit logical addresses and a page size of 4 KB. How many entries are required in a single-level page table?

2^20
2^12
2^32
2^16

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Calculate page offset bits: 4 KB = 2^12 bytes, so offset = 12 bits.
Calculate page number bits: Total bits - offset bits = 32 - 12 = 20 bits.
Number of entries = 2^(number of page bits) = 2^20.

Answer: 2^20

Example 3 · level 3

Which statement correctly differentiates a binary semaphore from a mutex?

A mutex has ownership; only the thread that locked it can unlock it, while a binary semaphore has no ownership.
A binary semaphore can be used for signaling between threads, but a mutex cannot.
A mutex can have a count greater than 1, whereas a binary semaphore is limited to 0 or 1.
Both provide the same semantics; the terms are interchangeable.

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Remember mutex = mutual exclusion with owner thread.
Binary semaphore = signaling primitive without owner.
Select the option that mentions ownership.

Answer: A mutex has ownership; only the thread that locked it can unlock it, while a binary semaphore has no ownership.