Unlocking a Pentium 1

[Crashman]

I have several regular Pentium (P54C) and Pentium MMX (P55C)CPUs which are the later version with the multiplier locked by pins. Does anyone know where I can find the documentation for these pins so I can unlock them?

Cast not thine pearls before the swine

 

[Crashman]

You can tell if it's a newer version if it won't overclock beyond 100, but chances are that it won't run that fast anyway. While some 100's will accept either 2x (for 2x50) or 1.5x (for 1.5x 66), the 75/90, if locked, will not go beyond 100. I have seen an unlocked P75 reach 166, but since the chances of one going that fast are slim, the only processors that use locks that matter are the 120/133 (2x cannot be changed), 150/166 (2.5x cannot be changed), 180/200 (3x cannot be changed), and 233 (3.5x cannot be changed). For instance, it would be nice to make a 233 go to 100x2.5, but I mainly ask for overclocking slower processors on older boards (making the 133 go to 166, etc.) Some of these have the clock speed etched on the bottom. I already found the documentation.

Cast not thine pearls before the swine

 

[jlbigguy]

How can you unlock them? From my understanding, the pins are "cut" or disabled within the chip itself.

If possible, I would love to get my daughters 200mmx running at 266 or higher. Best I can do is 225 @ 75mhz FSB.

<font color=blue>This is a Forum, not a playground. Treat it with Respect.</font color=blue>

 

[Crashman]

OK, if your sure you want to try this-
The original specification for up to 200MHz showed BF1 open, BF0 open to be reserved, but the specification update that included the 233 showed that setting to be 233MHz. So disabling pin BF1 (BF0 is already disconnected internally)should make your processor go to 233 as long as your motherboard supports it.
There are adittional settings available that require BF2 to be opened. These additional settings came about as a result of faster Pentium MMX processors being released for the mobile market. At least 266 and 300 are available. For 266 to be active requires BF2 to be opened and BF 1,0 to be closed. Because the pinout graph does not show BF2 to be on the processor itself, I must assume that it is either a new pin added to the Mobile version, or that it is on the motherboard itself. So unless you can figure it out, the best I can suggest is the 233 setting, which would be 262.5 for 75MHz.

Cast not thine pearls before the swine

 

[74merc]

how about a little more info Crashman.
got a url I can look at?
I've got a 133 sitting here that I am playing with on a test Linux box...

----------------------
Independant thought is good.
It won't hurt for long.

 

[Crashman]

<A HREF="http/support.intel.com/support/processors/pentium/" target="_new">http/support.intel.com/support/processors/pentium/</A> give you a list of avaialble documents. I con't remember which ones I downloaded. I tried modifying the pins on a 200 but without good results-I think the pins have to be connected internally. You might be able to modify a 150/166 to 200 by blocking BF0 simply because these have both connected internally, but as for any others, good luck. I have not tried modifying a 166 yet because I am out of stock on these.

Cast not thine pearls before the swine

 

[Crashman]

Not true-only the multipliers are controlled by the proccesor. Voltage is regulated by the motherboard, not the processor. The processor tell the motherboard what to set it at. Which means that you can raise your voltage simply by wiring a VID pin to VSS using a fine wire. The motherboard cannot tell whether it is internally or externally connected. I raised a Celeron FC-PGA 1.5v 566 to 1.7v by wiring in Vid3 to VSS and disconnecting Vid2. It works on all motherboards capable of detecting that voltage.

Cast not thine pearls before the swine