Pentium 90 (P54C) multiplier modification?

[caps_buster]

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: http://rapidshare.com/files/202992710/Asus_TXP4-X.pdf
( http://capsmod.net/forum/viewthread.php?tid=342 )
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... :o

Anyone got some clues there?

[caps_buster]

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: http://www.intel.com/support/processors/pentium/sb/cs-011038.htm
http://processorfinder.intel.com/details.aspx?sSpec=SU031
http://support.intel.com/support/processors/pentium/sb/CS-023718.htm

[celemine1Gig]

I just had a look at the manual for your board. I don't know if a multiplier of 1x is even possible at all, but what is strange is that according to the manual page 17, the "BF2" signal is not used. So maybe you could try and see what happens when you place a jumper for "BF2".

IMHO, it's worth a try, considerung that the parts are not really expensive. So what do you have to lose? :)

[caps_buster]

True. However, nothing has happend. I quess that the Pentium 90 has LOCKED the multiplier into the x1.5 settings.

The question is, witch Socket 5/7 CPU has it UNLOCKED or witch can be modified to have x1 ... or modified to unlock :p:

Intel support is really funny. First they are telling me that documentation for Pentium (1) I must BUY (?!?!) and then - Intel is announcing the discontinuation of interactive support for the... well, for almost every older CPUs. That suxx :down:

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 http://amd.com
clicked on the Support & drivers
then clicked on Technical Documentation
...and then ERROR: 404 Not found

ROFL :rofl: :ROTF:

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

[Cheffy]

i think the old cyrex prxxx cpu's ran funky multipliers and might be worth checking:

on 66mhz bus, and set to board multi of 2.5 (2.5*66=166mhz) it run at 113mhz or close to that O.o?

dont try with K6-2 or K6-3, as far as i remember the K6-2 and 3 have a min multi of 2x. and the 2x multi is internally re-mapped to 6x. giving 6x, 2.5x, 3x, 3.5x, 4x, 4.5x 5x and 5.5x - they are however atleast fully unlocked. and the P200mmx i played with wasnt locked atall either nor the amd K5

[caps_buster]

Yep, if they can do x1 multiplier, then I'm definitively interesed. ATM it looks like that only Pentium Overdrive can do it. With disconnected fan it should set itself to x1 multi. The question is where to get one working Socket 5/7 Pentium Overdrive, regardless of it's default clock. Looks like kinda scarce CPU... Some pieces are on eBay, but from China and not tested - eg. if a dead Pentium Overdrive come, you can't even blame them... Damn.
Not to mention the pricetag they ask for not tested and kinda obsolete and useless todays piece of HW. Did I mention possibly not even working?

Pentium Overdrive 166MHz
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&Item=230223333937&Category=3674

Pentium Overdrive 166MHz MMX
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&Item=230244893667&Category=15921

[Cheffy]

http://cgi.ebay.com/AMD-K5-75-AMD-SSA-5-75ABR-CPU-GREY-TOP-tested-RARE_W0QQitemZ310126162463QQcmdZViewItemQQptZUK_Mo therboards_CPUs?hash=item310126162463&_trksid=p3286.m63.l1177

thats the old K5 i was talking about, seems its as expensive as the pentium OD's O.o
iirc it oced well, from 75mhz to something like windows boot at 120-130mhz