about Limit Maximum CPUID to 3 options

about Limit Maximum CPUID to 3 options

Hi there,

we use E5450 cpu, Windows Xp 32bit in the HP XW6600 workstation.
There is an option named "Limit Manximum CPUID to 3", the default value is Disabled, and Windows starts up normally. When I set this option to Enabled, the Windows Xp starting up is very very slowly, about 5 mins.
and we also have some HP Z600 workstations, with E5540 cpu and Windows Xp 32bit os runing. on Z600, setting this option to Enabled, and windows will be starting up normaly.

Could someone please tell me some detail of the "Limit Max CPUID to 3" option, it looks like an option for Intel CPU only.

many thanks,

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Quoting - andrew.chenys
Hi there,

we use E5450 cpu, Windows Xp 32bit in the HP XW6600 workstation.
There is an option named "Limit Manximum CPUID to 3", the default value is Disabled, and Windows starts up normally. When I set this option to Enabled, the Windows Xp starting up is very very slowly, about 5 mins.
and we also have some HP Z600 workstations, with E5540 cpu and Windows Xp 32bit os runing. on Z600, setting this option to Enabled, and windows will be starting up normaly.

Could someone please tell me some detail of the "Limit Max CPUID to 3" option, it looks like an option for Intel CPU only.

many thanks,

Here's some useful info: http://www.techarp.com/showfreebog.aspx?lang=0&bogno=307.
To sum it up: this option is only useful if you are using an operating system that does not recognize all of the features of your processor. I don't know exactly why your OS is slowed down by enabling it, but since it's windows XP, which has no problems with E5450, you will probably never need to have it enabled anyway.
This site explicitly recommends that you have it off for XP and Vista: http://www.overclock.net/3371220-post2.html.

Quoting - Tudor

Here's some useful info: http://www.techarp.com/showfreebog.aspx?lang=0&bogno=307.
To sum it up: this option is only useful if you are using an operating system that does not recognize all of the features of your processor. I don't know exactly why your OS is slowed down by enabling it, but since it's windows XP, which has no problems with E5450, you will probably never need to have it enabled anyway.
This site explicitly recommends that you have it off for XP and Vista: http://www.overclock.net/3371220-post2.html.

Thank you Tudor.
We use a homegrown PCI adapter on HP workstations. On HP Z600, we must set the BIOS option to Enabled, otherwise, the communication using the PCI adapter will abort when McAfee VirusScan Command Line running.
We also use HP XW6600 workstations, but it has the booting performance problem with the BIOS option to Enabled.
Yesterday, HP sent me a special BIOS version for xw6600, the booting performance problem solved, but the communication problem is still existing.

Could you please show me some demo codes (c/c++ codes is welcom:))about how to query the processor to find out the highest input value CPUID recognizes? I want to test the difference between HP Z600 and HP XW6600 using windowsXp.

I just find http://www.intel.com/assets/pdf/appnote/241618.pdf , and made a test of the maximum value of CPUID with 'MOV EAX, 00h', on HP xw6600 (with oneE5450 processor).
The test result are:

HP BIOS Option: Limit Maximun CPUID value to 3=Disabled
return:
EAX:0000000a (Largest Standard Function Number Supported)
EBX+EDX+ECX=GenuineIntel

HP BIOS Option: Limit Maximun CPUID value to 3=Enabled
return:
EAX:00000002 (Largest Standard Function Number Supported)

EBX+EDX+ECX=GenuineIntel

Question:
I think the EAX should be 3 when I set the option as Enabled, but it returns 2 on HP xw6600.
It should be 3? or 2?

no more ideas?

Maybe this is a lost in translation

value 3 = 3 (four values 0, 1, 2, 3)
values 3 = 2 (three values 0, 1, 2)

Jim

www.quickthreadprogramming.com
Best Reply

Quoting - andrew.chenys

no more ideas?

"Limit to three" means levels 0, 1, and 2 will be reported -- standard C array counting applies since it is starting from level 0.

Just the enumeration of the remaining CPUID levels should not slow down the OS startup. There is something fishy going on. I would use bootvis to do a boot+drivers trace with limit enabled and disabled to compare the driver initialization times and see which one is responsible for the slowdown. My psychic powers lead me to believe thar the culprit is most likely the homegrown PCI adapter driver followed by the McAfee filesystem filter driver. Removing them one by one and measuring startup time with limit disabled seems like a good starting point as well.

Regards,
Igor Levicki

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