Is it better to have two cores or four logical processors?

Question

My system has two physical cores, and four logical processors. To my understanding this means that I have four CPUs due to Hyperthreading, and work is distributed as evenly as possible. However, I have a BIOS option that disables Hyperthreading, giving me only two CPUs to work with.

If I turn this option on, what would be expected? Would my system speed up or slow down? If I was running something that uses all the CPU such as Folding@home, would I notice an increase or decrease in productivity?

Solution

Hyperthreading allows for the CPU to stay active and to never go idle during a load. Lifehacker made a nice post based off of from As fast As Possible's YouTube video explaining this technology by theory and metaphor. It is a nice read and Linus in the YouTube video does a great job explaining it.

If Hyperthreading is on, it keeps the processing more at a stable overall speed and makes workloads that don't require the processes to be consecutive (i.e. rendering in Blender, video editing, and heavy multitasking) a noticeable amount faster. While if your professes require them to be done in order (i.e. computation math equations) it my make no difference at all to a slight decrease in performance. I think that you would see at least a noticeable increase in performance in Folding@home, especially if you're running other tasks at the same time, but this would depend on the programming and optimization of the application. How ever much hyperthreading helps, it isn't the same as double the processing cores, but it is overall better to keep it on for much faster multitasking and risking the possible tiny decrease in productivity and performance once in a blue moon.

Hope it helps!

Comments

[Ramhound]

Realistically there is no difference. There is virtually zero downside to Hyperthreading compared to physical cores in Intels current product line. If you disable Hyperthreading the you can only run 2 threads at once compared to 4

[Admin]

@Ramhound So it might make the computer slower because it can only process 2 commands at a time instead of 4?

[Ramhound]

It will make a multi-threaded application slower, the pc, won't be slower specifically

[Admin]

It appears that this is answered in the folding@home FAQ: Hyperthreading is a technology used on Intel CPUs to improve parallelization of computations. A dual-core CPU with hyperthreading enabled appears to the operating system as a four-core CPU. Each physical core powers two logical cores, so in reality hyperthreading does not actually double the CPU’s performance. Hyperthreading is usually enabled in the BIOS by default, and we recommend that it stays enabled, as the SMP cores can use it to process Work Units faster.