Unlocking & downclocking a Pentium II?

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Unlocking & downclocking a Pentium II?

Postby static- » 2017-11-26 @ 20:57

Hi Vogons!

I'm going through all my old PCs I've upgraded over the years and am looking to make an all-around decent DOS/win98 machine, with stronger focus on DOS end.

One of my computers is a Pentium II-ECC 400Mhz with an Asus P2B motherboard which I figure should be perfect. I was also curious if I could downclock it for older games.

When I go into the BIOS features, as the bios draws the screen I can see a quick flash of a selection menu for changing the clock speed multiplier, but then it disappears. So my guess is my Pentium II is locked. I see "CPU Internal Core Speed: 400MHz" but cannot change it.

Does anyone know if it can be unlocked and allow me to downclock when needed? I found this page which seems to say you can do it if you block one of the PINs:

http://www.overclockers.com/forums/showthread.php/67133-Unlocking-the-PII-Tutorial-(Warning-Large-Photos)

Does anyone know if this actually works? There are no pictures that I see (broken links?), but it describes which PIN.
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Re: Unlocking & downclocking a Pentium II?

Postby Scali » 2017-11-26 @ 21:10

I don't think most Pentium II CPUs are locked in the first place.
I have an Asus P2B-LS with a Pentium II 333 on there, and afaik I can just select any bus speed and multipliers that I want.
I've had it running at 350 MHz without a problem at least (bus speed to 100 MHz instead of the 66 MHz at its stock speed). I've also had it run at 400 MHz, but it requires extra cooling.
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Re: Unlocking & downclocking a Pentium II?

Postby static- » 2017-11-26 @ 21:24

Perhaps only some are. I see the option in my Asus P2B bios but it disappears after the bios screen finishes loading, like it's realizing the CPU is locked so hides the option from UI
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Re: Unlocking & downclocking a Pentium II?

Postby Scali » 2017-11-26 @ 21:32

static- wrote:Perhaps only some are. I see the option in my Asus P2B bios but it disappears after the bios screen finishes loading, like it's realizing the CPU is locked so hides the option from UI


Yea, according to Wikipedia, later models were multiplier-locked, and some even locked to 66 MHz bus:
https://en.wikipedia.org/wiki/Pentium_II
Towards the end of its design life, Deschutes chips capable of 500 MHz within Intel cooling and design specifications were produced. However, these were not marketed. Rather than destroy already multiplier-locked units, those Deschutes units that had been tested and locked with a multiplier of 5 were sold as being 333 MHz. This was accomplished by disabling the 100 MHz bus option. Overclockers, upon learning of this, purchased the units in question and ran them well over 500 MHz; most notably, when overclocking, the final batch of "333 MHz" CPUs were capable of speeds much higher than CPUs sold at 350, 400, or 450 MHz.


Mine is an early Deschutes 333 model, and not locked in any way afaik.
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Re: Unlocking & downclocking a Pentium II?

Postby static- » 2017-11-26 @ 22:18

Seems as though mine is already at 100Mhz. It would just be nice to have a downclock option
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Re: Unlocking & downclocking a Pentium II?

Postby BitWrangler » 2017-11-26 @ 23:49

Might be a hidden option in that BIOS, try shift F1 or Ctrl F1
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Re: Unlocking & downclocking a Pentium II?

Postby static- » 2017-11-27 @ 00:04

Thanks for the suggestion, didn't seem to do anything.

I found the manual and funny enough it says this:

CPU Internal Core Speed (350MHz)
This function is reserved for future use and is currently disabled

Maybe there is a way to access it?

Actually I'm on Bios 1011 but looks like there are newer..
http://soggi.eu/files/motherboards/bios ... 3_beta.txt

But nothing specific to this. I should try it out.
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Re: Unlocking & downclocking a Pentium II?

Postby Deksor » 2017-11-27 @ 00:23

I've read stories on the internet from the late 90's telling that some germans managed to figure out how to unlock the multipliers. Unfortunately nobody explained how they did. I can't say if that's true or not ... I've also read on an old article presenting the Abit BH6 that said that some of the early locked chips could be unlocked by signaling them as 66MHz bus CPUs. Unfortunately I wasn't able to reproduce this. I'm not sure if that's just because it's a fake (though it come from a well known website) or if I really need a deschutes CPU from mid/late 1998
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Re: Unlocking & downclocking a Pentium II?

Postby BitWrangler » 2017-11-27 @ 00:34

Some slot 1 stuff toward bottom of page here... https://www.ocinside.de/workshop_en/intel_overclock/
Basement full of ancient PC stuff, starting to go through it. Most recently toyed with DOS era stuff 15 years ago, so memory might be rusty. So what's this BitWrangler guy's deal ??? >>> http://www.vogons.org/viewtopic.php?f=25&t=56382
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Re: Unlocking & downclocking a Pentium II?

Postby static- » 2017-11-27 @ 01:44

I tried updating to the latest BIOS. It was successful, but the option is unavailable. Shfit-F1, Ctrl-F1, Alt-F1 also didn't work.

I guess my motherboard doesn't support it, or my CPU is locked. I was hoping for a BIOS option out of convenience specifically for selective underclocking.., oh well!

Thanks all for the suggestions.
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Re: Unlocking & downclocking a Pentium II?

Postby idspispopd » 2017-11-29 @ 09:15

Doesn't the P2B have jumpers to change the FSB? At least that's what Google tells me. Of course that may depend on the revision...
In that case you could change the FSB from 100MHz to 66MHz.
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Re: Unlocking & downclocking a Pentium II?

Postby Scali » 2017-11-29 @ 11:31

idspispopd wrote:Doesn't the P2B have jumpers to change the FSB? At least that's what Google tells me. Of course that may depend on the revision...
In that case you could change the FSB from 100MHz to 66MHz.


Yea, it's still 'oldskool', my P2B-LS (basically the same board, but with the optional LAN and SCSI controllers onboard) also requires you to jumper in the speeds. But mine works.
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Re: Unlocking & downclocking a Pentium II?

Postby FFXIhealer » 2017-11-29 @ 15:22

I've got an ASUS P2B Revision 1.02 and it has the jumpers to both set the FSB speed and the CPU multiplier. I always kept mine at 3.5x @100MHz FSB for my Pentium II, but for the new Pentium III in the system, it ignores the CPU multiplier altogether. I've never tried overclocking or underclocking the Pentium II, so I can't tell you about that. But I do know that Phil's Computer Lab talks about DISABLING CACHE to make a fast processor slow as dog-shit in order to play Wing Commander - which is the one DOS game that is ALWAYS referenced by people trying to make the system slower. Maybe disabling cache is something you could try.
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Re: Unlocking & downclocking a Pentium II?

Postby meljor » 2017-11-29 @ 18:14

My 333 p2 can go as low as 2x multi and i think my 300 (66fsb version) and 266 can do that also.

So the lowest would be 2x 66mhz = 133mhz on 440BX.

Some 440LX boards can go even lower as 66mhz fsb and can do 60 and 50mhz fsb. So it should be possible to run some p2 cpu on some LX board at 2x50mhz.
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Re: Unlocking & downclocking a Pentium II?

Postby static- » 2017-11-29 @ 18:19

Yeah jumper route should definitely work.. I just hoped it'd be something that could be done from BIOS directly to not have to open up the CPU case. I guess I could wire some switches or something :) I just found it interesting that in the BIOS you can see the options there but they disappear once the screen finishes refreshing. I should try to take a picture.

And yes, disabling cache is very handy! .. and accessible from BIOS. I have to try Wing Commander.. but it does pretty well for Ultima VI. Also THROTTLE.EXE works well too.
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Re: Unlocking & downclocking a Pentium II?

Postby sprcorreia » 2017-11-29 @ 21:45

meljor wrote:My 333 p2 can go as low as 2x multi and i think my 300 (66fsb version) and 266 can do that also.

So the lowest would be 2x 66mhz = 133mhz on 440BX.

Some 440LX boards can go even lower as 66mhz fsb and can do 60 and 50mhz fsb. So it should be possible to run some p2 cpu on some LX board at 2x50mhz.


My ASUS P2B allowed for 2X multi and 50MHz FSB, but would loose L2 cache. There is a minimum multi to keep L2 active.
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Re: Unlocking & downclocking a Pentium II?

Postby gerwin » 2017-11-29 @ 23:49

sprcorreia wrote:My ASUS P2B allowed for 2X multi and 50MHz FSB, but would loose L2 cache. There is a minimum multi to keep L2 active.

I used to experiment a lot with these things. Pentium II Deschutes core has no setting to do 2x with L2 cache enabled, But the earlier Klamath core does have a setting of 2x with L2 working. However, Klamath also has a jumper setting with 2x and non-working L2.

I don't have enough data to pin the week exactly, and it may also depend on the fab location, but to my knowledge Intel started locking the Pentium II processors around week 33 of 1998. Year and Week can be read from the markings on the plastic SECC-1 cartridge. There is no unlocking method.
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Re: Unlocking & downclocking a Pentium II?

Postby idspispopd » 2017-11-30 @ 10:22

static- wrote:Yeah jumper route should definitely work.. I just hoped it'd be something that could be done from BIOS directly to not have to open up the CPU case. I guess I could wire some switches or something :)

I'm pretty sure somebody posted about connecting the turbo switch to the FSB jumper on the mainboard. But with a P2 you probably don't have a turbo switch.

Did you have a look at SoftFSB? Or maybe there are other tools to do this?
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