From: faruque@sun.soe.clarkson.edu (Abdullah Faruque,334CH,3752,2654247)
Subject: Re: How to INCREASE PROCESSOR SPEED (recommended?)
Organization: Clarkson University
Date: Wed, 18 Nov 1992 22:09:32 GMT

From article <wiegand.722013797@lido16>, by wiegand@rtsg.mot.com (Robert Wiegand):
> y70q@jupiter.sun.csd.unb.ca (LAM) writes:
> 
>>In article <7347@kielo.uta.fi> f1sami@uta.fi (Samu Mielonen) writes:
>>>A subject of increasing processor speed by changing the crystal on 
>>>motherboard has popped up in this newsgroup a couple of times. This
>>>sounds very interesting, but I wonder if anyone has used this method
>>>to increase system performance without any loss in reliability. Anyone
>>>care to share their experiences?
> 
>>I heard from my friend that there are guys in Hong Kong change the
>>crystal of a 486DX2/66 to a 40MHz crystal. The machine instantly
>>changed to a 80MHz machine. I know nothing further about this.
> 
> This will definatly reduce the reliability of the machine both in the short
> term and in the long term.
> 
> In the short term you will increase the possibility the soft errors
> (one time glitches) bu running the parts faster than their rated speeds.
> 
> In the long term you reduce the lifetime of the parts due to increased
> heat form the higher operating speed.
> 
I am running a 486DX-33Mhz at 40Mhz without any problem. I put an
extra fan and heatsink to cool down the CPU and now the CPU is running
at a much lower temp that it is used to run at 33Mhz (without any
extra cooling). So, probably the long term effect, due to the extra
heat generated by over running it, is zero. Actually it may even
prolong the life, because it is running much cooler (with a fan and
heatsink) than the max operating temp specified by the manufacturer.
Normally, the manufacturer specifies the max operating temp of a CPU
(or in general any semiconductor device) under certain operating
conditions. If you increase the operating frequency then you must also
provide necessary cooling to keep it under the max rated temp.

Now the question is that how far you can increase the speed. There is
no rule here, it may run at only 1% or as high as 30% above the rated
speed. There are design limitations beyond which it will not work at
all, even if extra cooling is provided.  You have to do the experiment
and find out the max possible speed that can be obtained without any
soft error for a particular CPU. I found that a 486DX-25 can run at
33Mhz and a 486DX-33 can run at 40Mhz without any problem. But again
that may not be true for all 486DX25/33 chips available. So, far I did not
encounter any problem running DOS 5.0, Win 3.1, OS/2 2.0 and many
other diagnostic and application softwares.  I even pushed a 486DX-33
to 50Mhz just to see what happen. I was surprised that the system
booted up and most DOS based programs run (even Checkit passed all CPU
tests), but Win 3.1 and OS/2 2.0 did not run at all when pushed to
50Mhz. I also pushed a 286-16 and a 386SX-16 to 20Mhz an both run perfectly.
You have to consider the following things when pushing a CPU.

1. You must provide extra cooling to run it below max operating temp.

2. The motherboard must be rated at or above the intended speed.
Otherwise you are looking for troubles ( in some cases it may work,
but most of the time it will not work properly).

3. Check extensively with different OS, diagnostic and application
softwares before you settle down at the intended speed.

3. The main memory and external cache (if any) must meet the speed
requirement necessary to run without putting any additional wait
state. If you have to put additional additional wait state, then you
will loose performance and pushing the CPU may not even justify in such
case.

6. Increasing the system clock will also increase the BUS speed clock,
which is  derived by dividing the system clock. In most new motherboards
there is an option to select the BUS speed in the CMOS setup. So, reset that
option as close to the previous setting, otherwise the system may not even
boot up. The standard AT BUS clock is 8Mhz. You can go as high as 12Mhz if
all of your cards (Vedio, HD/FD controller etc) can run at that speed.

5. Pushing the CPU and replacing the crystal may void the warranty.
So, do not go for it if you care about the warranty.

6. If you do not feel confident enough to do the experiment, then do not even
think about it. Not recommend at all for those who even hesitate to open
the computer case.

Please do not flame! I saw this topic several times, so I just
compiled my experience here which may or may not be useful to others.

-Faruque
Email: faruque@sun.soe.clarkson.edu




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