Hyper Treading Technology

[Oct714]

Hi there,

Need some help to fully understand the advantages/disadvantages of using a CPU with Hyper treading technology.

I have a P4 Prescott 3.4GHz w/HT, and 2 GB RAM 3200 Dual Channel. When HT enabled in BIOS, Device Manager will show my system as a multiprocessor system with 2 "virtual" CPU's.

I know that by using Task Manager/processes, I can "set affinity" for most of the applications in memory (force application to use either CPU "0" or CPU "1")

Now, here comes my confusion. If I do not set affinity for some applications, I will not get any advantage of having a HT CPU? Aplication will be handled by "both" CPU's (as if HT is not enabled)?. If I do get advantage, although I have heard not all applications will benefit of HT(is it true?), should I notice a significant improvement of the performace of my pc?

Also, given the speed of the CPU and RAM, if I only use office and web surfing, I should not notice any improvement if HT is enabled, right? But if I use a little more complex software (video editing, music creation, etc), enabling HT should or should not give me a significant increase in performance?

I have noticed that when rendering video (after effects) I get a CPU usage of up to 95% (w/o HT) Now, correct me if I am wrong: if I enable HT with after effects and set affinity to one CPU only, I should notice a decrease of performance since I am forcing after effects to use only 1 CPU (50% of the physcical CPU)?

How Due Core would handle all this?

[cohenx]

Well, forcing an application/task to use "only" CPU "0" isn't useful, since Windows XP manages that itself.

You get advantage of having a HT CPU most of the time when there is more than one thread to execute. If you only run "After Effects", it depends if this is coded multithreaded. If you run "After Effects" and another task in the background, for example video or audio player, you will for sure have an advantage with a HT CPU.

I have noticed that when rendering video (after effects) I get a CPU usage of up to 95% (w/o HT) Now, correct me if I am wrong: if I enable HT with after effects and set affinity to one CPU only, I should notice a decrease of performance since I am forcing after effects to use only 1 CPU (50% of the physcical CPU)?

Wrong, thats not a "real" Duo Core CPU. In fact, I would estimate no change of performance when you set affinity to one CPU only.

How Due Core would handle all this?

Duo Cores can handle identical threads at the same time, a HT CPU can only handle different threads at the same time, because the 2 virtual CPUs have to share their ressources (If CPU "0" calculates floating point, CPU "1" cannot calculate also floating point at the same time. A Duo Core can do that.)