Just for info. I purchased a 200 MHz MMX. I was able to overclock the
bus frequency and achieve:
Bus Speed CPU Speed (from boot msg)
66 MHz => 200 MHz
75 MHz => 230 MHz
83 MHz => 250 MHz
The 200 MHz part uses a 3.0 bus multiplier. I then tried the 1.5
multiplier that works for 233 MHz part, and SURPRISE, the chip came up
at 233 MHz! I then tried the 75 MHz bus speed and the chip went to 266
MHz. When I tried the 85 MHz bus speed the chip said it was still a 266
part, but couldn't read the disk to boot linux.
Bus Speed CPU Speed (from boot msg)
66 MHz => 233 MHz
75 MHz => 266 MHz
83 MHz => 266 MHz (but dosen't operate correctly)
The actual execution times for compute bound tasks is near identical
even with the 6% clock increase. For 1024x1024 FFT (of a single
precision image) it took 1.7 seeconds while at 266MHz it took 1.71
seconds, a 0.5% increase. So the increase in memory speed caused by the
83 MHz bus clock (up 10%) balances the the increase in CPU clock speed.
For now I have deceded to be conservative, not pick on the memory or PCI
devices and run at 75MHz. Anybody know how to get the 85MHx bus clock
to work?
don
-- ******************************************************************* * Don Fisher dfisher@as.arizona.edu * * MMT Observatory VOICE: (520)621-7647 * * University of Arizona FAX: (520)670-5740 * * Tucson, AZ 85721 * *******************************************************************