Future Domain SCSI controller for AT bus

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In article <1996 at spdcc.COM>, dyer at spdcc.COM (Steve Dyer) writes:
> 
> it works is a little weird.  Apparently the current (< 2.3) versions
> of XENIX are said to "only support two drives (of any type)".  This
> would mean that if you have a AT floppy/hard disk controller with
> at least one of the disks in use, you don't have the option of adding
> another controller of any type.  Now, no one can really tell me why
> that is, since UNIX really doesn't care, and the best explanation I
> can surmise is that the XENIX "divvy" partitioning software layer
> makes such a bad assumption, so two drivers for two different
> controllers which both use the "divvy" partitioning scheme can't coexist.

The problem is not Xenix, but the way IBM designed the AT.  What happens
is that most controllers use the same interrupt.  The AT cannot support
multiple devices with the same interrupt.  Also, they both might be using
the same address space.  Either or both of these situations will cause 
problems.  Perhaps some of the hardware types will be able to shed some
more light on the matter.

Jonathan Bayer
Intelligent Software Products, Inc.