Misunderstanding the difference between single-threading and multi-threading programming

Question

I have a misunderstanding of the difference between single-threading and multi-threading programming, so I want an answer to the following question to make everything clear.

Answer 1

It depends.

How many cpus do you have? How much I/O is involved in your tasks?

If you have only 1 cpu, and the tasks have no blocking I/O, then the single threaded will finish equal to or faster than multi-threaded, as there is overhead to switching threads.

If you have 1 cpu, but the tasks involve a lot of blocking I/O, you might see a speedup by using threading, assuming work can be done when I/O is in progress.

If you have multiple cpus, then you should see a speedup with the multi-threaded implementation over the single threaded, since more than 1 thread can execute in parallel. Unless of course the tasks are I/O dominated, in which case the limiting factor is your device speed, not cpu power.