[Coco] FD-500 Floppy Drive

Roger Merchberger zmerch-coco at 30below.com
Sun Oct 24 16:24:08 EDT 2010

On 10/24/2010 02:29 PM, Arthur Flexser wrote:
> My vague recollection is that Commodore disks might not have an index hole,
> needed on the CoCo only for formatting.  This is a hole adjacent to
> the center of the disk, both in the disk itself and in the envelope
> containing it.  You can make one with a paper punch if you're careful.

I can't say about the Commie drives; I never was enough into that 
hardware to know for sure if it *required* the index signal. The drives 
were certainly non-standard enough that it's quite possible.

I can tell you, however, that the Apple ][ series drives *did not* 
require any "hardware" index -- there was a software index that Woz 
designed into the drives.

I remember using my "Apple Flippy" disks that had only the 2nd 
write-protect notch cut in the disks (and worked fine) and I was quite 
puzzled at first when I tried to reformat the disks on the Tandy Model 4 
systems, the "normal" side would format fine, but the "back" side would 
not. I can say, cutting the notch for the index signal was much more 
"harrowing" than nipping out a 2nd write protect notch.

The advantage to the Apple system is that you could use either soft 
sectored (one hole) or hard sectored (one hole per sector, there were a 
couple of standards) floppies without worry.

As far as I know, all disks had an index hole for the primary side - to 
retool an entire manufacturing line to remove a hole that only a few 
machines didn't use (and didn't care existed anyway) would have been 
quite costly.


My advice to the OP would be to see if there's a way of getting a small 
program onto your CoCo (type it in, DriveWire, etc.) that can check the 
rotational speed of your drive system. I'm pretty sure they existed 
(back in the day, anyway) and were fairly accurate. If there's 
fluctuation in the spindle speed, that could cause the issues of which 
you speak. This could be done with any known good floppy, no special 
disk was needed.

To check for drive alignment, however, that did require a special disk 
(Dysan was one of the big name brands for those) and an oscilloscope, so 
it's a bit more outside the scope of a "weekend tinkerer."

Hope this helps!
Roger "Merch" Merchberger

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