2 hardrives of different interfaces allowed to coexist?

[Dick Dunn]

teoh at uicbert.eecs.uic.edu writes:
> Is it possible to allow 2 different types of hard disks in a pc UNIX
> environment (using 2 different controllers)? If so, what are comments
> on AT IDE vs ESDI drives?

It is possible to mix controller types, as long as you apply the care you'd
expect, to avoid interrupt and I/O port conflicts.

IDE and ESDI are both fairly inexpensive ways to get disks a bunch faster
than old AT ST-506 (MFM) drives.  IDE is usually cheaper; IDE drives tend
to be smaller.

>...Is it true to say that the AT IDE drive is dependent on AT architecture
> machine?...

Yes, in the sense that the "IDE" interface is mostly a way to extend the
relevant parts of the "ISA" (AT) bus.  That's not to say you can't make an
IDE controller for some other bus; it's just that IDE is most closely
matched to ISA.

The win with either IDE or ESDI--or, to look at the other side, the loss in
the old ST506 interface--is that the old style has a separate drive and
controller with a rather slow interface between the two.  It is this
interface (which is standard) that limits the data rate.  ESDI keeps the
drive/controller split but ups the data rate.  IDE puts the controller on
the drive; the maximum IDE data rate is determined by the ISA bus.

One thing to keep in mind about IDE:  The interface matches that of a
primary disk controller on the AT bus, and you get a max of two IDE
drives.  After that, to add more disks you'd have to add them on a
"secondary" AT-style controller (standard or ESDI) or SCSI.

> I was planning to use the slower 80MB as secondary drive for back up
> purposes or storing files of lower priority, and leaving all the executables
> in the faster drive. Will there be any substantial loss of performance w/
> this configuration?...

Performance shouldn't be that much of a problem--just move things around if
the slow disk is getting too much use.  Even staying with a slow disk, you
can improve performance if you've got an old 2:1 or 3:1 controller by going
to a 1:1 controller.  These are in the neighborhood of $100.
-- 
Dick Dunn     rcd at ico.isc.com -or- ico!rcd       Boulder, CO   (303)449-2870
   ...Are you making this up as you go along?