From: khoo@husc15.harvard.edu
Subject: Upgrading the processor on 386/486 machines
Organization: Harvard University Science Center
Lines: 43


In case anyone was wondering about upgrading their 386 or 486 class machine
without spending a lot of money, I looked into replacing the processor
on those machines and here are the facts (as I understand them).

If you have a PS/2 Model 70 or Model 80, you can replace the i386 chip with
either 1) a Cyrix 486DLC chip for $130 which will increase your processing
power by about 60% for normal fuctions, and not at all for math functions.
This chip will only run at your original clock speed, ie. if you have a 16MHz
machine the Cyrix 486DLC will run at 16MHz.
note: Windows does not use the math functions, so it is a good upgrade if
you are running Windows.
Or, 2) you can get a Kingston 486/NOW platform for $450 with a 25MHz i486SX
on it which will increase your normal processing power by about 100%, if you
were running at 25MHz originally. But again it will not increase the speed
of your math fuctions.  I think that it will continue to run at 25MHz even
if your original processor runs at a slower speed.
There is also 3) the Kingston 486/NOW platform for $750 with a 33MHz i486DX
on it.  This might speed up your math functions as well, but I am not sure.

If you have a PS/2 Model 70 B21 or other PS/2 machine with either an i486SX
or a non-clock doubling i486DX (ie. it runs at either 25 or 33MHz) in it,
then you can get an Intel Overdrive chip (which is really an i486DX2 chip) and
replace your chip with it.  You should get about 95% better preformance for
both normal and math functions.  The 25/50 Mhz version of the Overdrive chip
costs $450 and the 33/66MHz version costs $700.  The replacement for the
25MHz 486SX chip is an espeacially good deal as it provides the math
coprocessor which the 486SX does not have.  Note that the speed ratings on the
Overdrive chips are the maximum speed at which they can run.  If you have a
20MHz 486SX, then the Overdrive chip will run at 20/40MHz, ie. 20MHz externally
and 40MHz internally.  There is no reason to buy an Overdrive chip which is
rated at faster then your machine, you will not get faster performance.

You should be able to buy these chips from any of the microchip merchants that
advertise at the back of PC Magazine or PC Week.  You might want to shop
around as prices do vary.  If you need a name/phone number for a source for
a particular chip, e-mail me, and I will respond with a couple of sources.

Lawrence Khoo

-- 
khoo@husc3.harvard.edu       Lawrence Khoo       Computer Consultant
khoo@haavelmo.harvard.edu    (617) 496-8992    Econ. Dept, Harvard U.