On Sat, 16 Jan 1999, Tony Duell wrote:
> > > *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.
>
> 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
> 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_at_cts.com
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Don Maslin - Keeper of the Dina-SIG CP/M System Disk Archives
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Received on Sat Jan 16 1999 - 18:00:41 GMT