Concurrency vs Parallelism: What Is the Difference?

Concurrency vs Parallelism

Definitions

Concurrency Multiple tasks appear to run simultaneously but may interleave (possible on single core)

• Focus: managing and switching between tasks
• Analogy: one chef handling multiple dishes by switching attention

Parallelism Multiple tasks truly run simultaneously (requires multiple cores)

• Focus: actual simultaneous computation
• Analogy: multiple chefs each making one dish

Relationship

• Parallelism is a subset of concurrency
• You can be concurrent without being parallel, but not parallel without being concurrent
• Concurrency is a design concern; parallelism is a hardware concern

Implementation by Language/Framework

Language	Concurrency	True Parallelism
Node.js	Event Loop + async/await	Worker Threads
Python	asyncio / threading	multiprocessing
Go	Goroutines + Channels	Yes (GOMAXPROCS)
Java	Threads	Yes
Rust	async/await + tokio	Yes