[Coco] [Color Computer] Max number of disk drives?

[John E. Malmberg]

Allen Huffman wrote:
>>What's the maximum number of disk drives you can connect to a CoCo
>>assuming you are going through a MPI?
>  
> That said, there was a hack that let the control lines address way more 
> disk drives than normal.  Originally we could have, what, 6 drives max 
> (single sided)?  Then with double sided, I think it was three.  You had 
> one line for side select, then 2 lines for the actual drive?  The hack 
> was a hardware mod that read those lines binary and then did the actual 
> switching of more drives.
> 
> Someone at the Atlanta CoCoFest in 93 or 94 or 95 was telling me about 
> it.  But I can't remember how many drive select lines there are to know 
> what the actual number was.

With the COCO hardware, there are 3 drive select lines wired and 1 side 
select lines.  The controller is apparently ignorant of their contents 
and passes them through.

So with software driving them and a binary decoder on each drive, you 
can have 8 double sided drives one string.

The Model 3/4 used two different cables and sent two drive select lines 
to each and a side select line, so the same trick would still limit it 
to 8 double sided drives on the two strings.

Of course there could have been other hacks.

And interesting project might be to drive one of those old tape backup 
units that connect to a floppy controller like the one on the superboard.

-John
wb8tyw at qsl.net
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