16 Jan
1999
16 Jan
'99
10 a.m.
On Sat, 16 Jan 1999, Tony Duell wrote:
Actually, you can have 4 _per controller_, for a total of 8 drives.
The original PC and XT controller has 2 drive connectors. One is a 34 pin
card edge used for the internal drives. The other is a DC37 on the back
panel used for the external drives. Each connector has 2 drive select
signals and 2 motor-on signals.
The AT controller, alas, only has the internal connector, so it only
supports 2 drives. But in theory it would be possible to have an AT
controller with 2 drive connectors. The enable bits for the extra drives
are simply called 'reserved' in the output registers, nothing to stop
them being used as they were on the XT.
Unfortunately all the single-chip floppy controllers only support 2
drives. Great pity...
Not true, Tony, if you are talking FDC chips. The CompatiCard IV is a
single chip, as are the WD FOX and some DTK cards and others as well.
- don
*Why we are limited to 2 floppy drives in DOS
Actually, you can have 4, if you have a controller at the secordary floppy
controller address as well as at the primaryfloppy controller address.
Each controller can only have two drives because of a silly hardware setup
chosen by IBM. The Linux floppy driver (or at least the one in this
old kernel) will
support 8 drives like that. 4 of them (drives 2 and 3 on each controller)
are normally disabled in software, but it's a trivial, and documented,
patch to enable them
-tony
donm(a)cts.com
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