Socket 370 Pentium III Engineering sample experiments \ VOGONS

Socket 370 Pentium III Engineering sample experiments

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First post, by Pino

Posted on 2025-10-29, 20:32

Pino Offline

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I have 3 Engineering sample socket 370 CPUs: a Coppermine Celeron 1.1Ghz, a Coppermine-T Pentium III 1.0Ghz (with heatspreader) and a Tualatin Celeron 1.4Ghz.

The Coppermines are operational and fully unlocked, I'm testing it on an Asus CUVX, both are OK overclockers, I haven't pushed much, but I can do 133Mhz x 9 = ~1.2Ghz on both.

Unfortunately I don't have a socket 370 motherboard that supports Tualatin to test the 3rd one.

Of course the point of my experiments were to try to slow down this CPUs, lowering the multiplier to see if I could bring it down to play speed sensitive DOS games.
Since the CUVX motherboard have an ISA slot this would be a great all round machine for DOS games all the way to high end Win98 if I could make it work.

The problem I'm facing is that I can't select the lower multipliers available on the MB BIOS (see the highlighted values in the picture attached).
If I select 2.5x it goes to 9.5X and etc. The minimum I can select is 5.5X.

So the question is, is there a way to force the lower multiplier value on the left side of the table?

Thanks

Reply 1 of 1, by p5p6p7

Posted on 2026-04-20, 07:38

p5p6p7 Offline

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As you perhaps already know: the motherboard can communicate via 4 bus ratio pins to the CPU.
Therefore, there is a maximum of 2^4 = 16 internal frequency settings.
The multipliers on the left side have in part been "recycled"/reassigned for Coppemine CPUs to enable certain multiplier increments above 8.
Therefore, there is no way to avail lower multipliers on the left side.

However, only 14 rows are listed in your multiplier list. These 14 correspond to pin low/high permutations except for all low or all high.
Meaning, there are two remaining settings, namely, all four pins low and all four pins off.
These two settings both correspond in the Pentium II to a multiplier of 2.0
Though, iirc I have also seen a baseline ratio of 4.0.
Perhaps you can avail this setting with "safe mode" to boot with such a lower multiplier (?)
Note, there is also a minimum core frequency iirc. Meaning stability is not only limited upward but also downward.
I estimate, if the bios allows you to boot into the safe mode selection, then you will boot with a multiplier of 2.0 or 4.0
You might have to increase the FSB speed if the resulting clock is too low for the CPU.

Alternatively, you could perhaps locate the 4 bus ratio pins on the CPU or socket (better on the dismounted socket) and insulate them.
This should result in a multiplier of 2.0 or 4.0 as well.
However, it is not advisable to temper with a precious unlocked engineering sample. Better to perform this on the dismounted socket.

Your CPU is listed as a quantification sample in some data bases. Quantification samples are frequently only downwards unlocked.
The question I wonder, can you avail a multiplier of 11.5, meaning, a multiplier above the rated 11.0?
You stated that e.g. 5.0 is not available to you. One could infer that thus, the ratio on the right is available. But in some CPUs simply all settings above the rated multiplier yield a ratio that does not exceed the rated ratio (here 11.0).
That would be an interesting clarification. You could adjust an FSB off 66MHz to safely investigate whether your sample is also upward unlocked, whether it allows a multiplier of 11.5. Perhaps you tried already.

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