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Michael Karcher
Michael Karcher
6:59 PM
Are you sure your 386 system uses a high-speed bus? Typically, 386 boards run the ISA bus at 8MHz, which contributes to memory cards on that bus being slow. Furthermore, 386DX systems suffer from the reduced memory width of just 16 bits on the ISA bus.

Running the ISA bus at unconventianally high speed did happen up to around 12MHz on 286 system. As the slowest 386SX speed rating is 16MHz IIRC, I don't think there ever were 386 boards *designed* to overclock ISA that much. Of course, there are boards that support ISACLK = FSB/2 for 16MHz processors and happily accept that configuration at …
 
fuz
fuz
7:40 PM
The 386 box I have has an i386DX at 25 MHz
the BIOS has the option to run the ISA bus at 1/2 or 1/3 cpu clock or at "AT bus speed" whatever that is (probably 8 MHz)
without the memory card, the system runs fine with ISACLK = 1/2 FSB speed, so at least the other cards seem to cope fine with the higher bus speed
 
Michael Karcher
Michael Karcher
8:14 PM
OK, I understand. "AT bus speed = 1/2" is meant for 16MHz, and 1/3 is meant for 25MHz. With 1/2 at 25MHz you are indeed overclocking the ISA bus, and memory cards failing at that timing is not surprising.
 
fuz
fuz
8:33 PM
yeah
hm maybe setting this to 1/3 will do better
curiously, only one of the three memory extension cards I have seem to work
the other two misbehave
 

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