how do i know hyperthreading is on?

i have a p4-2.40b (c1 stepping). wcpuid says it has HTT... buuut how do i know its really there and working??

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Originally posted by df
i have a p4-2.40b (c1 stepping). wcpuid says it has HTT... buuut how do i know its really there and working??

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C1 does not mean HT. AFAIK only the 3.06 has HT to date ;)

ok. that answers that.. just wondering why the hyperthreading flag is on in cpuid flags if its not really there?

On POST, you would see two identical CPUs and in Windows, your system would be recognized as a dual system.

I think you have a stepping of the core with HT technology in there, but not working (a finalized version, not the Jackson Tech core logic which all P4s have had).

Tom's Hardware talked about this:

http://www6.tomshardware.com/cpu/200..._306ht-02.html

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In contrast with its direct predecessor, the 2.8 GHz P4, the new CPU has a major new benefit - its Hyper-Threading technology has now been enabled. What has been hidden from the user up until now is that Intel already integrated its Hyper-Threading technology into the Willamette core two years ago. Software developers were able to access this function right from the start for research purposes. It is not possible to activate HT on older P4 CPUs, because certain settings in these chips are permanently disabled.

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There's a discussion going on here: http://www.vrforums.com/showthread.p...5&pagenumber=1

Also, I'm sure WCPUID checks for HTT by running the CPUID instruction and checking the value returned in one of the registers. Since the newest chips are probably all made on the same mask, the CPUID instruction should return the same values on any current stepping of the CPU. CPUs with HT (for now the 3.06) and those without HT probably differ in some later stage where Intel might blow fuses (as they do to set the multiplier) or something along those lines to really enable or disable HT. It would seem to me that a company that goes as far as to put the actual speed of the CPU on the namestring, wouldn't leave it entirely upto the BIOS to limit HT.

This is why I think WCPUID shows HTT as enabled (because the program is basically just a GUI representation of the x86 CPUID instruction), but try as one might, they won't be able to actually activate it on a CPU that's not supposed to have it.

Hope that helps.

If someone is familiar with x86 assembly and wants to try this out themselves, they can use the CPUID instruction to find out for themselves how WCPUID reports HTT supported. Supported does not mean enabled, as this program would show (it returns the number of logical processors).

Its just a register value after executing WCPUID with the correct value in the EAX register (in this case 1).

Here's some sample x86 code I wrote to check this (my dated assembler won't support the CPUID instruction so I can't post the actual working program):

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MAIN PROC FAR
    PUSH DS ;INITIATE THE PROGRAM
    XOR EAX,EAX ;CLEAR EAX
    PUSH EAX
    MOV EAX,1H ;INITIATE CPUID
    CPUID
    MOV DX,EBX[23:16] ;CHECK COUNT
    MOV AH,9
    INT 21H ;DISPLAY COUNT
    RET
MAIN ENDP

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I just wrote that quickly, so bear in mind it might have bugs, and like WCPUID, it will be fooled, so even if it returns a 2 (HTT supported CPU stepping), it doesn't mean your specific CPU has HT enabled. Enabling it would require Intel to do so during production.

Check out page 17:
http://developer.intel.ru/download/d...s/24161822.pdf

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Originally posted by Ramuman:
On POST, you would see two identical CPUs and in Windows, your system would be recognized as a dual system.

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You can open Device manager in WIN XP/2000 , go to Processor sub menu , you will see two identical CPUs.
It means that HT is enabled

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Originally posted by shev_milan07


You can open Device manager in WIN XP/2000 , go to Processor sub menu , you will see two identical CPUs.
It means that HT is enabled

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Exactly, for all intents and purposes you have 2 identical P4s if you have HT -- just with one set of execution resources, cache, bus bandwidth etc. ;).

People talk about having to disable HT in dual xeon systems because win2k only accepts 2 processors - the OS sees the primary processor and it's second virtual identity and put's *that* down as the second processor instead of the second actual cpu... then leaves the second chip to waste completely... My question is this... Is there a bios feature that needs to be switched on in order for HT to run? (Win2k server, by the way works fine with 2 xeon's and HT enabled...)