🚀 go-pugleaf

In <1319@alsys1.aecom.yu.edu> manaster@yu1.yu.edu (Chaim Manaster) writes:

>In article <C18A2L.Dtx@hkuxb.hku.hk> h9117228@hkuxa.hku.hk (Li) writes:
>>The slowdowns are probably due to a change in the system clock (40MHz
>>for the 386 to 25MHz for the 486DX2).  The boot-up (a lot of disk
>>accesses) and video speed are dependent on the ISA bus speed.  I'd bet
>>his bus speed is set at 1/5 ACLK (8MHz for a 40MHz system clock, but
>>5MHz now for 25MHz system clock).  Changing it to 1/3 ACLK should fix
>>it.

You're right. I overlooked the most likely possibility.

>How does one change ACLK? Is this a variable somewhere? (DOS, BIOS
>etc?) Is this a hardware signal? (In which case a user can't change
>it?) If it is a variable please be specific on how to find it and
>then how to change it (temporarily and permanently).

It's - like the settings I suggested to you - in the BIOS setup. At
least, it's there in all (?) modern PC clones.  The names may vary
a bit, but under 'Advanced Chipset setup' you should find something
like
          AT Bus Clock     CLK/5

This is the factor that the master clock (which you just changed
from 40MHz to 25MHz) is divided by to give the ISA bus clock (which
should equal 8MHz, but most machines work with 10MHz or even more).

If you can't find this entry, it is most probably set by jumpers
on your motherboard.  In that case you should refer to the
motherboard manual for further information.

The decrease in startup speed and video I/O are certainly NOT
caused by the decrease in CPU clock speed because [1] A 25MHz
486 in burst mode outperforms a 40MHz 386 for raw I/O speed and
[2] video speed is mainly limited by the video board and the ISA
bus throughput, not by CPU I/O.

Success,

Peter Herweijer
pieterh@sci.kun.nl