- 2068 Bhadra · 3 marks
Real and pseudo-parallelism
Short answer
Real parallelism occurs when multiple processing units execute tasks truly simultaneously, providing true speedup. Pseudo-parallelism is rapid time-sharing on a single CPU, making tasks appear concurrent but only one executes at any instant. Real parallelism requires multiple processors; pseudo-parallelism uses context switching.
What do you mean by real and pseudo-parallelism?
Real parallelism
Several tasks really execute at the same instant, because the system has more than one processing unit (multiprocessor, multicore CPU, cluster). Each process or thread has its own CPU. Total work finishes in less time, so it gives true speed-up.
Pseudo-parallelism
Only one CPU is present, and the OS switches rapidly between processes (time-sharing, context switch every few milliseconds). Because of the fast switching, it appears to the user that all processes run at the same time, but at any instant only one executes. It is also called concurrency or logical parallelism.
| Basis | Real parallelism | Pseudo-parallelism |
|---|---|---|
| Execution | Truly simultaneous | Interleaved, one at a time |
| CPUs needed | Two or more | One |
| Speed-up | Real | Only better CPU utilisation |
| Overhead | Communication/synchronisation | Context switching |
| Example | Quad-core PC | Multitasking on single-core CPU |
✓ Answer checked by Claude Opus 5.5 (high effort)
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