[Coco] 3.5" drives on coco 3

[Fred D. Provoncha]

For years back in the late '80's and early '90's I ran my OS9 Level 2 
system on my Coco3 with just one 5 1/4" drive. I even wrote my fractal 
generator Mandel09 on that system, using just that one drive. It's a 
pain to have to keep swapping disks all the time, but it's doable. A 
couple of years after I got my system back up and running, around 2002, 
I finally added a 3 1/2" drive to the system. I modified the drive 
cable, and crammed the 3 1/2" drive into my FD-502 case. It was 
difficult to get the cable connected to both drives; not much space 
inside that case, and the cable was just barely long enough.

RSDOS sees the 3 1/2" drive exactly the same as how it sees the 5 1/4" 
drive. From RSDOS's point of view, there is no difference. When RSDOS 
formats a disk in the 3 1/2" drive, it formats it as a 35 track, 
single-sided disk. It only uses 186k of the 720k that is on the 3 1/2" 
disk. That's fine with me, I don't care about wasting all that unused 
space on the disk. The reason I use a 3 1/2" drive is not to get more 
space on a disk, but because 3 1/2" disks are more durable and easier to 
find than 5 1/4" disks.

Nevertheless, I find I'm not getting as much use out of my 3 1/2" drive 
as I thought I would. When working with RSDOS, I still use my 5 1/4" 
drive more often. That's because a lot of my RSDOS games that are on 5 
1/4" disks are copy-protected and so cannot be transferred to 3 1/2" 
disks. Also, a lot of RSDOS games are hard-coded to run in Drive 0; my 3 
1/2" drive is wired up to be Drive 1. That also prevents me from booting 
up OS9 from a 3 1/2" disk. I haven't been able to figure out how to 
modify OS9Boot to have the system boot entirely from Drive 1.

The 3 1/2" drive is nice to have, though. Anything not copy-protected 
and not hard-coded to use Drive 0 has been copied onto 3 1/2" disks, and 
using them is sweet!

Fred Provoncha
Stansbury Park, UT


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