Hi Mike,

 MR> The issue with ISA cards, incidentally, is whether or 
 MR> not they perform bus mastering DMA.  Since ISA slots only 
 MR> have a 24-bit DMA available to them, they limit OS/2's direct  MR>
addressing ability to 16MB.  Anything above that 
 MR> is used as fast swap space.

While the 16MB direct Bus Master DMA limit is true as you say, it actually
depends a lot on the driver for the ISA card. When I upgraded the BBS machine
from a 16Mb 486DX2-66 to a 32Mb K6-300 I changed the Adaptec 1540C to a PCI
NCR based card because of the ISA DMA issue, but this change seemed to result
in a moderately rare (every 15-20 days operation), but totally fatal
reliabilty problem. 
While researching driver updates for the NCR card I discovered that a refresh
of the OS/2 AHA154X.ADD file appeared early 1998 which allowed me to enable
Double Buffering -

  BASEDEV=AHA154X.ADD /V /DBUFF /ET

Using the above parameter it allows the card to work fine and was a great
help, I have (had) about 3 of these cards lying around here. 

Of course there is a little catch in that it can require an extra move of the
data in memory before the application can have it, reducing performance by a
small amount, but at least it keeps a good reliable old card still usable.

Cheers.........pk.


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