🚀 go-pugleaf

In article <218@ima.UUCP> johnl@ima.UUCP (John R. Levine) writes:
>Look again.  The standard IBM controller handles two 10 MB disks.

In fact, the controller in newer IBM XTs will handle any combination of two
drives out of four drive types.  Three of these four types are 20 meg
drives.  I am writing this article on an XT with 2 Seagate ST-225 (20 meg)
drives hooked to its IBM controller.  To tell if your controller is of this
newer type, look for a four position dip switch near the mounting bracket.
Older controllers have solder pads and silk screen markings where this switch
could be mounted, but no switch.  Older controllers will also handle any two
out of four drive types (if you add the switch), but the types are different.
I suspect (but do not know) that the only difference between the older and
newer XT controller is the switch, and a different ROM (the ROM contains the
fixed disk bios including the disk type table).

This information is taken from the "IBM Technical Reference, Options and
Adapters."  The relevent sections are "IBM Fixed Disk Adapter (#6361503)"
(for the older XT controller), and "IBM PC 20MB Fixed Disk Drive Adapter
(#6139790)" (for the newer controller).

Write me if you need to know what drive types are supported, or what the
switch settings are for a particular drive type.
-- 
Dave Shanks             ..!tektronix!tessi!atelabs!cds
AT&E Laboratories
1400 NW Compton  Suite 300
Beaverton, OR  97006
(503) 690-2000