Pentium 90 (P54C) multiplier modification?

By trodas ยท 8 replies
Feb 27, 2009
  1. An old Pentium 90 CPU (P54C) has internal multiplier x1.5 - so it make from the 60MHz FSB the 90MHz clock.

    I do wonder, however, if that multiplier can be set to x1 ;)

    Usually people want to overclock, however I would like to try underclocking and the x1.5 multiplier suxx. If I understand good the multiplier settings, for example for the Asus TXP4-X Socket 7 board:
    ( )
    Then setting BF0, BF1 to 1-2, 1-2 (manual, page 17) let the CPU internal multiplier be used, so, if I can modify the multiplier somehow (burning internal path? connecting two pins?), then I got the underclocker dream machine.

    Anyone know if that is possible or know someone who might know?

    Another possibility is the Pentium Overdrive, but dunno where to obtain one and if it ever run at x1 multi. Any other ideas, beside rare 5V Pentium 60/66 witch use Socket 4 and hence are not very usufull as the nice underclocker board has Socket 7 (5) ...

    Another idea pop into mind and that is the Mobile Pentium or Mobile Pentium MMX chips for laptops, but I have no idea either where to get one of these, besides I have no idea if they can run with the x1 multi... :eek:

    Anyone got some clues there?
  2. Justin

    Justin TS Rookie Posts: 942

    This is an interesting project, but I wonder what your aim is for this? You won't be doing much to reduce power consumption or heat - most energy consumed by the CPU is lost as heat and is due to the CPU voltage, not the clock frequency. Or is there some other reason?
  3. raybay

    raybay TS Evangelist Posts: 7,241   +10

    It can be done, but you are asking for disaster from the OS or other components. But it might be a fun experiment. See some of the programmer sites.
  4. trodas

    trodas TS Member Topic Starter Posts: 29

    Soul Harvester -
    Today I'm in second place, as for the lowest CPU clock reached and verified by CPUZ:
    And I would like 1st place. I'm just 0.55MHz shy of 1st place, so if I convince the board again to FSB 7.14 and having x1 multiplier - the resulting frequency will be 7.14MHz. A guaranteed WR...

    Either this, or much harder way - reduction from Pentium 60 or 66 (Socket 4) to Socket 7 (5) has to been made, together with the voltage supply (creating add Vcore powering - 5V for the Pentium 60 or 66) and then using the x1 multi and reaching 7.14MHz.

    And then there is a possibility of... etc. :-D

    raybay -
    Sounds great, you sure it can be done?
    As far as the disaster goes, well, I already noticed how exceptionally hard was to save the CPU-Z validation already, since at 7.14MHz FSB the default keyboard and mice in PS/2 ports refuse to work... so... I know all about it.
    Witch sites do you recommend?
  5. Bill_Bright

    Bill_Bright TS Rookie Posts: 21

    I am not sure I would assume the CPU would run, even if you could modify the board to run at 1:1. Not to mention the RAM, I/O controllers, and any other devices dependent on that clock. But, for the sake of argument, let's assume they would. Which two pins would you short? Which runs would you open? Without a full "service manual" with detailed schematics for that specific model AND revision number (very important!) I could not begin to tell you which ones.

    :( :suspiciou

    Wow! You get around Trodos. I wish I had researched first before I wrote the above. Please note that many sites consider cross-posting poor forum etiquette! It keeps multiple volunteer resources from helping others and it can result in confusing and conflicting advice. As an admin of your own site, I would think you would be aware of that.

    As a member of the staff at, where I was about to answer your post when I found this one. I note you asked this question at these sites too:
  6. trodas

    trodas TS Member Topic Starter Posts: 29

    Well, I'm pretty sure the CPU will run at 1:1 with FSB, however I'm more inclined to think that Pentium (1) have internal multiplier. Only in some unlocked cases you can externaly change it, but that is not the case of Pentium 90 - not to mention the board did not have x1 multiplier settings.

    So the question is - how to modify the Pentium to force it into x1 multi?

    As far as the documentation goes, well, if I have it, I would figure it out myself already, so I asking about that because I did not have it. Intel sell (!!!) some documentations that might be interesting, like:

    Pentium Processor Technical Overview - 241610
    AP-579: Pentium Processor Flexible Motherboard Design Guidelines - 243187
    AP-479: Pentium Processor Clock Design - 241574
    Pentium Processor 3.3V Clock Driver Specifications
    Pentium Processor 3.3V ASIC Interface Specification

    However I did not seems any way to buy them:

    As far as your personall attacking goes, I will not comment that, because you are lecturing me here about net etiquette and yourself breaking it badly. It is obvious that I ask on any forum I know, when I did not getting answer anywhere. But - nevermind then.
  7. Bill_Bright

    Bill_Bright TS Rookie Posts: 21

    I'm breaking it? Not hardly. Or else I would have commented everywhere like you did. And I did try to answer your question here, after all.

    I'm not sure you can - it does look like it will let you go to x1.5, x2, and x2.5, depending on the exact model, but I don't see x1.

    The link in that document does not seem much help, but right below that it provides an address and phone number.
  8. trodas

    trodas TS Member Topic Starter Posts: 29

    True, but I'm not US resident, so... So I emailed Intel about it and they told me:

    "Intel is announcing the discontinuation of interactive support for the..." well, for almost every older CPUs. That suxx :(

    So I wonder, if any of the also supported Socket 5/7 CPUs by the board, such as Cyrix 6x86 PR166+, K5 and K6 (some even claim K6-2 or so works well) can be forced to accept x1 multi.

    So I go to the
    clicked on the Support & drivers
    then clicked on Technical Documentation
    ...and then ERROR: 404 Not found


    Is that a IT joke, or AMD way of support? :rolleyes:
  9. Justin

    Justin TS Rookie Posts: 942

    This is certainly a prospect.

    trodas, have you considered using a Socket 4 Classic Pentium, 60 or 66MHz variety? As I recall, they were host-based clocks - locked at 1:1.
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