Difference between

[Basil Alias]

What is the difference between cores and threads.

[Electronics Wizardy]

Cores is how many physical execution units there are on a cpu to run code at the same time.

 

Each core has atleast one thread, but can have more, this allows the core to be better used as normally one logical thread can't full use all parts of one core.

[VeganJoy]

4 minutes ago, Electronics Wizardy said:

Each core has atleast one thread, but can have more, this allows the core to be better used as normally one logical thread can't full use all parts of one core.

How much extra performance does hyperthreading generally offer? 20-50% more? And in particularly optimized programs, isn't hyperthreading sometimes even bad for performance?

[WelshFruitSnacks]

Depends on the program. Single threaded stuff is actually hurt by multi threading sometimes. Its more if you have two unrelated programs so your (out of order) CPU core can keep executing code even if one thread has a cache miss or a long dependency chain to resolve. There was a (in order) processor had 8 threads in 1 core but each thread was only running at 1/8th the speed of the CPU because each thread would occupy a separate pipeline stage and exit before entering. So your multi threaded workloads don't see dependencies and stall so you essentially have a 100% performance core, but the single threaded stuff could run at most at 1/8th the theoretical performance.

[Electronics Wizardy]

18 minutes ago, VeganJoy said:

How much extra performance does hyperthreading generally offer? 20-50% more? And in particularly optimized programs, isn't hyperthreading sometimes even bad for performance?

Depends on the program, but normally 0-30%, depending on use.