486's and UNIX

[Michael Squires]

I had some problems with a 486/25 running under SCO ODT 1.0 that have
been traced to improper setup.  The board was (apparently) an MCT 486/25
baby AT with 8MB of DRAM using the OPTI chipset, AMI 486 BIOS.  The system
ran at about 1/3 the expected speed under UNIX but close to the expected
speed under DOS.  It turned out that the jumpers on the motherboard
that enable/disable the external cache overrode the XCMOS setup and
that the 8K on-chip cache was always enabled and its parameters were
set by the other XCMOS settings.  Changing the BIOS cache parameters to
cache off and all 8MB cachable increased speeds from 6900 1.1 Dhrystones/sec
to 21,000. (The XCMOS had arrived set for 1MB cachable, so the system cached
for DOS but not for UNIX above 1MB of physical memory.)

I tried the updated /boot from SCO but that had no effect one way or the
other.

Moral:  get docs from your vendor on XCMOS setup if you intend to use a
486 with UNIX.

Mike Squires (mikes at iuvax.cs.indiana.edu)     812 855 3974 (w) 812 333 6564 (h)
mikes at iuvax.cs.indiana.edu          546 N Park Ridge Rd., Bloomington, IN 47408
Under construction: mikes at sir-alan.cica.indiana.edu
-- 

Mike Squires (mikes at iuvax.cs.indiana.edu)     812 855 3974 (w) 812 333 6564 (h)
mikes at iuvax.cs.indiana.edu          546 N Park Ridge Rd., Bloomington, IN 47408
Under construction: mikes at sir-alan.cica.indiana.edu