07.003 How can I tell the difference between unlabeled DD and HD diskettes?
Description
This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
07.003 How can I tell the difference between unlabeled DD and HD diskettes?
3.5" HD (1.4MB) diskettes come with a square notch in the upper left
corner. DD (800kB) 3.5" diskettes do not come with this notch. In the early
days of PC computing, some PC users punched or drilled notch holes in DD
diskettes and used them as HD diskettes. If a 3.5" diskette has a circular
notch in the upper left corner, it is likely to be a DD diskette.
DD 5.25" (360kB) diskettes look very much like HD 5.25" (1.2MB) diskettes;
however, HD diskettes seem to almost never have a hub ring, while DD diskettes
usually do. The hub ring may be white paper, etc. and easy to spot or cut from
the same material as the diskette and barely noticeable. This difference has
been mentioned by Peter Norton (of Norton Utilities fame) in one of his books.
The hub ring makes it easier for the Apple Disk Drive II and other older
DD 5.25" drives to clamp and hold the diskette. Older DD drives also tend to
damage the center when there is no hub. If the hub ring of a DD diskette has
fallen off due to age, it's a good idea to transfer the contents to a new
diskette.
Otherwise, about the only observable difference is that DD diskette
surfaces often exhibit a more brownish cast whereas HD diskette surfaces are
generally dark grey or black.
The surest test for 5.25" diskettes is to place the diskette into an Apple
Disk II 5.25" drive and try to do a DOS 3.3 format. If it formats okay, it is
almost certainly a DD diskette. (This test will not always work with the newer
40-track drives. Some of these can get through a format with an HD diskette.)
By: Rubywand
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