On May 4, 2007, at 14:41 , Jon Hylands wrote:

> On Fri, 4 May 2007 20:35:21 +0200, "Damien Pollet"
> <damien.pollet at gmail.com> wrote:
>
>> Windows would probably report 100% CPU usage, but I doubt the CPU
>> would go twice as fast... HT means a single core can run instructions
>> from two threads simultaneously, not that the transistors are
>> partitioned into two half-cores. Surely all computing units are  
>> shared
>> among threads?
>
> No, with hyperthreading, the BIOS basically builds two virtual  
> processors,
> and each one gets half of the CPU speed.

I'm pretty sure this is not true, but more like what Damien wrote.  
Basically all that HT does is having a second register set so you can  
hold the state of two processes in the CPU at the same time.  
Execution units are shared. Since one process seldomly utilizes all  
execution units (due to "pipeline bubbles") the other process can use  
the free units. This simply enhances throughput, but it's not like in  
one process you only ever get half the speed.

- Bert -