What is Lock-Free?

  • Thread starter Thread starter NBK
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NBK said:
What is Lock-Free? Does the P4P800 Deluxe support it?

Thanks
NBK
Click to expand...

http://abxzone.com/forums/showthread.php?t=79631&highlight=lock+free

Lock free is simply utilizing a "safety feature" of some of the Intel
processors. A Prescott processor can either be a PRB=0 or PRB=1
part. The Platform Requirement Bit identifies whether the processor
draws 89W, or draws a higher number (up to 115W?). The higher
power processors have a feature, where they will only operate
at a 14x multiplier, unless the BIOS reads the PRB bit and responds
to it appropriately. When a high power processor is set up properly,
it will use its rated multiplier (x17 on a 3.4GHz processor), but if
the BIOS doesn't handle PRB properly, the processor stays at 14x
instead.

This originally showed up as a bug with Asus BIOS, where a high power
processor would only run at 2.8GHz. Then, the BIOS was modified, using
information obtained from Intel, so that later BIOS corrected the
flaw.

The marketing department got a hold of the info, and decided to
make the choice of x14 or "Normal Multiplier" as a BIOS option. By
doing this, an overclocker can specify the low multiplier, then
boost the FSB (and in turn, the memory clock), to allow higher
memory bandwidth, without necessarily having to overclock the core.
(Of course, if you push the FSB far enough, even the core gets pushed
past its normal rating.)

All this depends on how good a cooling system you've got. If you
find the CPU temp is always 70C, you are running in thermal throttle
mode, where the processor reduces the number of clock cycles during
which useful work is done. The processor will benchmark poorly in this
condition, so the cooling system must be able to get the CPU under
70C, for any benefit to be obtained.

Note that, in my description above, if the processor is a PRB=0 unit,
I don't think the choice of x14 or "Normal Multiplier" will exist,
because such a processor doesn't need a safety feature. So, if your
processor plus motherboard combo offers no x14 option, it could be the
processor is a PRB=0 unit. The safety feature was invented by Intel,
in case a "low power" Vcore design meets up with a "high power"
processor. With the two available load lines for processors, Intel
felt that some of the cheaper motherboards would support only the
89W processors, so the safety feature was added so that a high power
processor wouldn't damage a low power motherboard. As far as I know,
all the Asus Prescott ready boards support both - I've never read or
seen a suggestion they are limited to 89W processors.

The Intel documentation for this feature is coy about the whole thing.

Page 750 of this manual, tells you of the existence of the
MSR_PLATFORM_BRV bit 18 (the PRB bit), but doesn't describe how it works.
ftp://download.intel.com/design/Pentium4/manuals/25366814.pdf

A P4 datasheet, like this one, doesn't spell out the details,
but identifies different versions of processor via their PRB.
ftp://download.intel.com/design/Pentium4/datashts/30056102.pdf

This is the first article to tie it all together.
http://www.tomshardware.com/motherboard/20040916/asus_overclocking-02.html

HTH,
Paul
 
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