Which of the following is not an interprocessor communication mechanism in UNIX?

Correct option is D

Inter-Process Communication (IPC) mechanisms in UNIX allow processes to exchange data or coordinate their activities. The commonly recognized UNIX IPC mechanisms include:
· Pipes
· Message queues
· Shared memory
· Sockets
· Signals
A semaphore, however, is primarily a synchronization mechanism, used to control access to shared resources and coordinate processes. It does not itself provide a mechanism for exchanging data between processes.
Therefore, among the given options, the one that is not primarily an interprocessor/process communication mechanism is:
​$$\boxed{\text{(d) Semaphore}}$$​​
Information Booster
1. Pipe → Communication through a byte stream.
2. Message Queue → Communication through discrete messages.
3. Shared Memory → Processes communicate through a shared memory region.
4. Semaphore → Synchronization and mutual exclusion.
5. Socket → Communication between processes, including across networks.
Additional Knowledge
Why the Other Options Are Correct?
(a) Pipes — IPC
A pipe provides a communication channel through which one process can send data to another.
​$$P_1\rightarrow\text{Pipe}\rightarrow P_2$$​​
(b) Messages — IPC
UNIX provides message queues, allowing processes to communicate by sending and receiving messages.
(c) Shared Memory — IPC
Shared memory allows multiple processes to access a common region of memory and is one of the fastest IPC mechanisms.
(d) Semaphore — Synchronization
A semaphore is primarily used to synchronize processes and control access to shared resources. It is generally classified as an IPC-related synchronization primitive, rather than a data-communication mechanism.