On 23 Sep 98 at 14:59, George W Hurless wrote:

> I have a 486 sx2-50 with a 25/33mhz selection choice on the
> motherboard. I want to put in an upgrade cpu (amd 586-133) which
> says it will give 100mhz for a 25mhz board, or 133 for a 33 mhz
> board. If I switch to 33mhz on the board and install the upgrade
> chip, what other changes am I looking at? My system works ok now,
> just slow. I want to speed it up as cheaply as possible w/out
> messing it up.

  There are two things that could show up if you switch the board
from 25 MHz to 33 MHz.

1.  RAM speed
  If your installed RAM is rated for more than about 70ns -- 80 and
110 were once common -- it may not be able to keep up.  You may be
able to add "wait states" through the CMOS setup to compensate, but
IF you don't have L2 cache then this may eliminate much of the
effectiveness of the upgrade.

2.  ISA bus speed
  The ISA bus speed is often set as a fraction of the board speed.
For 25 MHz, this would typically be CLK/3, that is 8.33 MHz.  At 33
MHz, CLK/3 is 11 MHz, and CLK/4 is 8.25 MHz.
  Most modern ISA peripherals can handle 10 MHz just fine, but 11
could be pushing it.  You should be able to set this in the CMOS.

David G

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