question about WnXp and xeon DP w/HT

[SpiralDragon]

AFAIR winXp Pro suports only two CPUs... how does HT fit in if you have two Xeons and HT enabled? the CPUs would show up as 4... right? will WinXP use both phisical and HT CPUs? will it alow other aps to use all four segments?

[dZeus]

XP Pro only supports 2 physical CPUs. I don't think it'll have problems seeing extra logical processors and using them.

[DGhost]

WinXP Pro will handle 2x Physical HT processors just fine. You should see 4 processors listed in the task manager - 2 are physical, 2 are logical.

Windows 2000 on the other hand... since it is not HT aware, it will not be able to distinguish between physical and logical, and will only use the two physical processors (hopefully).

[isochar]

Win2k will show 4 physical processors... leading to all sorts of problems. Hence why HT is recommended off on Win2k.

[Byock]

First time I looked in Server 2003, and saw 4 CPU's, it threw me for a loop.

[SpiralDragon]

thanx guys

[VJ]

Just to confirm: I'm running XP Pro on a dual Xeon with hyperthreading enabled. As dZeus said, the limitation concerns two physical CPUs.
There are some neat things though:

1. In task manager, there are 4 CPU history graphs. The graph left of them (current CPU usage) is still just 1 graph. The history graphs are ordered as follows: logical 0 on physical 0, logical 0 on physical 1, logical 1 on physical 0, logical 1 on physical 1.
DGhost: all 4 processors you see are logical: for the system there is no difference between both CPUs from the same physical unit - there were a lot of discussions on this when the dual-CPU + hyperthreading emerged. As both logical CPUs from one physical CPU are treated identically (the one that needs available resources on the CPU gets them, no priority), you don't see physical CPUs as a user.

2. In the processes screen, the CPU time goes faster. So if your PC is running idle, after 1 hour, it will show 4 hours of idle time ! Suprised me at first... Also, a program that uses multiple CPUs will show the total CPU time used, not the total time you would measure with a chronometer.

3. I still haven't found where you can see that you are running hyperthreading: even in the system hardware, you see 4 CPUs showing up. Everything in Windows looks like there are 4 physical ones.

4. Initially, some softwares that use the number of CPUs for licensing purposes incorrectly assumed there are 4 CPUs present, and demanded a higher license. But I think by now those issues have been solved (could still occur if you intend to install older software).

Jörg