[Coco] Max number of floppy drives with DOS

Arthur Flexser flexser at fiu.edu
Wed May 19 10:58:03 EDT 2021

On the CoCo 3, in the normal all--RAM mode, switching slots will switch the
ROM, but that wouldn't normally matter since the ROM isn't in the memory
map.  (By changing only one nybble (4 bits) of the MPI poke, you could
switch the disk controller slot/address without changing which slot's ROM
would be in the map if you switched to ROM mode.  I forget which nybble is


On Wed, May 19, 2021 at 8:09 AM rietveld rietveld <rietveldh at hotmail.com>

> I am using a 512k coco3. I am running HDB DOS in my first controller and
> RSDOS in the second.  I BOOT up with HDB DOS . I know that HDB DOS is not
> being written over by RSDOS after I software select (POKE) the other
> controller because the second set of drives are still using the 6ms step
> rate . Just to be sure I pulled the ROM from the FD500 and i can still
> access those drives
> Sent from my BlackBerry Key2
> From: farna at att.net
> Sent: May 19, 2021 7:34 AM
> To: coco at maltedmedia.com
> Reply to: coco at maltedmedia.com
> Subject: Re: [Coco] Max number of floppy drives with DOS
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