GATE CS 1987 Q1-xvi — Concurrency and Synchronization

A critical region (also known as a critical section) is a portion of a program where shared resources (such as shared variables, files, or hardware devices) are accessed. To prevent race conditions and maintain data consistency, concurrent access to this region must be synchronized so that only one process can execute within it at any given time.

Let's evaluate the options:

• Option A: While semaphores ($P$ and $V$ operations) are commonly used to enforce mutual exclusion around a critical region, they are merely a synchronization mechanism. The definition of a critical region itself is independent of the tool used to protect it.
• Option B & C: These are incorrect and unrelated to the formal definition of a critical region in operating systems.
• Option D: This correctly and precisely defines a critical region as the segment of code where shared resources are accessed.

Therefore, the correct option is D.