Using Prescott Mobile Pentium 4's in desktop boards

[Wasmachineman_NL]

I have a ASUS P4P800SE with a Northwood Pentium 4 but the lack of SSE3 is holding me back. I was thinking of getting a Mobile Pentium 4 because of it's lower TDP (and possibly better binning?) but the question remains: can I use that type of CPU in my board?

[ApostolCV]

I saw links about pin mode for Pentium M on Prescott core.
But most of them are already dead.

[Calbris]

Yes, but that's assuming that it supports E0 stepping Prescott cores.

Thing is, you won't be able to use its maximum clock multiplier as SpeedStep is non-existent on the 82865PE+82801EB. That leaves you with a low 14x clock multiplier, which isn't very useful unless you were to perform a BSEL pin-mod to bring it up to 2.8 GHz. Then, an FSB overclock would be needed as a 2.8 GHz Prescott is quite anaemic/crap. I believe your P4P800 SE has a PCI/AGP lock and the ability to modify the FSB, so this shouldn't be a problem. Well, maybe the memory dividers and the RAM itself might be a problem.

A lower TDP does not always necessarily mean it's binned better than any other processor, I've seen a Core 2 Quad Q9550S that overclocked just about the same as a Core 2 Quad Q9550. On the other hand, I've seen a Xeon L3426 that overclocked much worse than a Xeon X3440.

[Wasmachineman_NL]

[wren4777]

Are there any 478 chipsets that can handle Speedstep?

[Calbris]

Apart from mobile Socket 478 chipsets, no. As far as I know, all desktop Socket 478 chipsets had no official support for SpeedStep.

Unofficially speaking, the 865PE (82865PE+82801EB combo) does support SpeedStep, but only in very specific boards such as the ASRock ConRoe865PE, ASRock ConRoe865GV, and the ASUS P5P800. Those are Socket 775 boards though, so that's out of the question.

[wren4777]

That makes sense. Can something like CrystalCPUID help with getting the multiplier back up?

[Calbris]

No, it can't. IA32_PERF_CTRL (MSR 0x199h) will always be read-only if SpeedStep is not supported. If that MSR is set to read-only, it would be impossible to change the core clock multiplier as it controls which multiplier is selected.

If you were to 'forcibly' enable SpeedStep via BIOS modification by setting bit 16 to '1' in IA32_MISC_ENABLE (MSR 0x1A0h), the motherboard wouldn't be able to detect the processor's switch to its maximum clock frequency as the motherboard has no pins dedicated to SpeedStep for it to signal a voltage increase to its VRM. This means you have a processor that is stuck on a core voltage of 1.15 V (for mobile Prescott) at its maximum core clock multiplier. As this takes place in the BIOS, it'd be inducing instability from the beginning which would probably prevent you from accessing the BIOS due to insufficient core voltage.

Unless you have a motherboard that allows the core voltage to be changed before the multiplier is set to the highest, this wouldn't be feasible in any case.

[wren4777]

Don't most 865PE and such boards allow changing the voltage? Meaning that, with that modification you described, a mobile Prescott could be run at max frequency?

[Calbris]

If you were to include the endless sea of OEM and non-overclockable motherboards, not exactly. But I do agree that most enthusiast motherboards are capable of changing the processor's core voltage.

Yes, but only in theory. I don't know the complications or side effects that might arise from this modification, as nobody (as far as I know) had performed this modification to a board that supports Prescotts by default.

You could try the BIOS modification and report back the results, if you are interested. I'm not, since I don't see a logical reason to do so.

[frag_]

There are some benchmark results on hwbot for mobile prescotts, some are with maximum multiplier on 865 desktop boards.
So it must be certainly possible to run at full speed.

[Calbris]

This submission in particular? It's the only one that has the maximum clock multiplier selected, but it could be a board that has a modified BIOS to go along with it.

All the other boards are using SS PTCA-01 adapters, at least that's what I can see.

[frag_]

There are some more.
https://valid.x86.fr/780346
https://hwbot.org/submission/4248199
https://hwbot.org/submission/3963584
https://hwbot.org/submission/2358162
https://hwbot.org/submission/2326832

Interestingly board is the same in all cases - Asrock P4i65G.
But users are different, likely this motherboard can do it out of the box.

Thanks for the topic!

[wren4777]

Thank you both for the info!

[Wasmachineman_NL]

I wonder if digitalbath's modded BIOS will help?