[Coco] Four floppy drives?

[Barry Nelson]

I once had 8 floppy disks running at once on a CoCo. I ran the floppy cable to a 4 line to 16 line demultiplexer chip and hooked drive select lines 0-2 into the inputs of that chip, I let the side select signal through untouched. Then I had 3 floppy cables coming out of the demultiplexer, one had lines select lines for drives 0-2 on the pins for 0-2, the next cable had select lines for drives 3-5 on the the pins for drives 0-2, and the last cable had the select lines  for drives 6 and 7 on the pins for 0 and 1. It worked under OS-9. Special OS9 drivers were required. Under disk basic only drives 0,2, and 4 were available. I set this up for a friend who ran a BBS.

On Jul 31, 2015, at 10:26 PM, coco-request at maltedmedia.com wrote:

> Date: Fri, 31 Jul 2015 15:25:08 -0400
> From: Arthur Flexser <flexser at fiu.edu>
> To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> Subject: Re: [Coco] Four floppy drives?
> Message-ID:
> 	<CA+LuDccNzenc1N5oXcTF+EUPw88UBezRMPyfyE8oW_3v4DM77Q at mail.gmail.com>
> Content-Type: text/plain; charset=UTF-8
> 
> It is puzzling how you managed to get 4 double-sided drives working.
> Ordinarily, only 3 would be available.  You have 4 drive select lines, but
> one would normally be used as a side select for double-sided drives.  I
> vaguely recall an article that described some scheme that recognized that
> when two drive select lines were simultaneously selected, a fourth drive
> would be accessed.  Did you do something like that?  Did you modify the
> Disk Basic ROM?
> 
> Art