[Coco] 3.5" FD drives

[Francis Swygert]

Date: Fri, 24 Jul 2015 23:09:17 -0500
From: Dave Philipsen <dave at davebiz.com>

There is a lot of discussion on this if you search the internet.  I have 
personally found that you can write DD disks in a HD drive without 
problems.  Others swear that you'll have a problem.  Since the HD 
floppies generally require a higher recording strength to store data at 
that density it makes sense that perhaps a DD controller may not have 
enough power to overcome a pre-existing HD format.  So it may be better 
to use non-formatted disks that have never been used to record HD.  You 
might also improve your chances by bulk erasing (degaussing) an HD 
diskette before using it as DD.
================================================
The problem isn't being able to write HD disks at DD, but the amount of time the data will remain valid. The HD disks don't "hold" data as long as DD disks when the HD is written at the lower levels with a DD controller. An HD controller can write an HD disk at DD and data will hold though. So you can use the HD disks to transfer data, but if you use it for back-up you may find that 2-3 years later the data is corrupt. I've used HD disks back in the day and read data back reliably several months later, but had been using the disk for saves over that time. Probably wasn't re-writing all the data, but a good bit of it. 20 years ago I'd heard of people creating long term backups with HD discs on their CoCo and finding the data corrupt after several years, but data saved on DD discs (5.25" and 3.5") was still valid 10 years or more later as long as the discs were stored correctly. 
 Frank Swygert
Fix-It-Frank Handyman Service
803-604-6548