How to distinguish between multithreading and parallel task execution concepts?

Multithreading and parallel execution are related but different concepts:

• Multithreading — the ability of a program to create and manage multiple threads within a single process. Threads can run simultaneously or alternately, switching on a single CPU core (concurrency).

• Parallel execution — the simultaneous execution of multiple threads or processes on different CPU cores or machines, which actually speeds up task completion.

Example:

• On a single-core processor, multithreading implements switching between threads, creating the illusion of simultaneous work.
• On a multi-core processor, threads can run in parallel, truly at the same time.

Thus, multithreading is a software model, and parallelism is a hardware capability.