On 17 Feb 99, at 18:22, Vincent Young wrote:

> I'm attempting to install a 56k modem on 486\dx4 100mhz cpu,33mhz bus
>
> the modem card doesn't use entire isa slot 12/16
>
> Can anyone explain why this would occur??

  I'm not sure what you mean by "12/16", but most ISA slots consist of
TWO connectors, one about 4" long and a second one about 2" long.
  The original IBM PC provided only the 4" connector, and supported
only transfers of 8 bits at a time.  The PC/AT added the second
connector so it could transfer 16 bits at a time.  [Although the
number of data lines was increased, there was no need to duplicate the
various bus "control" lines.]

  You may still encounter some devices which only transfer 8 bits at a
time, and so only use the 4" connector.  [Up into the 486 era, one
could find boards on which one or two of the ISA slots had only this
single connector....]  Few modems support 16-bit transfers, so they're
a common candidate for this simplification.


David G

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