[Tfug] Interchangeability of VRM's?

[Bexley Hall]

Hi Adrian,

On 12/12/2012 1:09 PM, Adrian wrote:
> On Wednesday 12 December 2012 10:39, Bexley Hall wrote:
>
>>> They could be changed dynamically, but presumably the processor would
>>> have to be halted during the change to prevent corruption.
>>
>> Does their state affect *performance*?  I.e., does tweaking the
>> core voltage buy you anything -- or is it "this core *requires*
>> this supply voltage"?
>>
>> (e.g., the performance of "classic" CMOS devices could be significantly
>> varied by altering their operating voltage)
>
> Yes, not directly affecting performance by itself (other than causing the
> processor to run hotter/out of voltage spec). But if you were a hardware
> tweaker trying to overclock the processor you would manually bump up the core
> voltage, say from 1.3V to 2.0V (beyond the processor spec), to increase the
> internal processor transistor response/decrease switching time to try and
> give yourself a better chance of getting that 200MHz CPU to run at a 500MHz
> system clock. This was also when people were pouring LN2 over their CPUs and
> such. Either it worked... or it went "poof" in a cloud of magic smoke...

Ah.  Never saw the appeal of that.  You want 500MHz?  *Buy* 500MHz!

You can push N2O into your engine for extra performance.
But, would you trust your *brakes* in those operating
conditions?  What would you think if you blew your engine?
"ooops"!

<frown>

And you're doing this, why:  to play a *game*??

>>> CPU required a different core voltage, changing the core voltage profiles
>>> was as simple as updating the firmware.
>>
>> ... in the BMC?
>
> Yes, though usually the BIOS firmware/BMC firmware was one indistinguishable
> package to the end user. Some motherboards (like the SC450NX) did break it
> out, you would have to upgrade both your BIOS and the BMC firmware to
> run/upgrade particular CPU combinations.

Yes, each of my servers has this sort of structure.  I had assumed
it also was concerned with the hot swap capability of the drives,
power supplies, etc. (monitoring, alarming, etc.)

>>> point the CPUs are "on". Alternatively, you could have the VRM lines held
>>> with pull-up/down resistors at power-on and then later have the CPU
>>> twiddle them
>>
>> But, they would still have to be pulled to their "nominal" levels.
>> I.e., you can't just arbitrarily pull them all high/low as this would
>> tell the VRM to supply a particular voltage to the core -- that it
>> might not be capable of tolerating (?)
>
> Correct, you would pull them to some nominal level that would work with the
> CPUs you had designed your motherboard to run with... Some other CPUs may not
> function correctly because the core voltage would be wrong initially, but
> hey.. your motherboard was never "certified" to run that processor anyways
> right?

So, these types of folks are content to "roll the dice"?