Gibsaw wrote:HD formats as DD no problem at all...
You're not going to get reliability using HD disks in a DD drive. HD formats as DD no problem in an HD drive only!
HD media has a thinner coating and double the coercivity of DD media. Thinner coating = lower read signal, higher coercivity = higher write current required.
QD is a different beast, it has the same coercivity as DD media but is certified to a higher track density (96 or 100tpi) - so it's just better quality media for drives that need it. Saying that, back "in the day" I'd never heard of problems using standard DD 48tpi media in Sord 100tpi mk III drives (and I'm guessing Commodore 8050 users found the same thing).