3-1/2" Floppy Market Cornered

From: Fred Cisin <cisin_at_xenosoft.com>
Date: Wed May 21 20:07:01 2003

On Wed, 21 May 2003, Marvin Johnston wrote:
> This brings up an interesting point; how do you tell the difference
> between DD and HD diskettes? My usual method was to try and format them
> on a DD drive, and if they formatted, they were DD :). Is there a better
> method?

That method will let some slip through that "almost" work.

Find one of each that are known, and labeled by the
manufacturer. Sometimes the labeling will refer to the UNFORMATTED
capacity and say 1M v 2M.
Find the write protect hole. Notice that on the HD diskette, there is
another similar hole in one of the other corners.
Go with whether or not the manufacturer put in that other "media
identification" hole. Once HD came out, every RESPONSIBLE manufacturer
of HD drives put in a switch to check for that hole. But if you have IBM
equipment, then YOU have to check.

Also for 3.5":
2.8M (4M unformatted) (Barium ferrite?) has a different media
identification hole.
Floptical (20M) has a different media identification hole.

Although LS120 drives will also take "regular" 3.5" diskettes, they are
thoroughly different in appearance.

There is usually a slight difference in color.
Also, when HD came out, they discontinued reinforcing the center hole.
Therefore, if there is no reinforcement, then it is EITHER a very early
"low" density diskette, or is an HD diskette.
If there IS a reinforcement, then it is either a DD diskette, or it is an
unreinforced diskette that somebody added a reinforcement to, by using an
aftermarket jig, such as from Inmac, or the Berkeley Microcomputer (later
Xenosoft) "Flip-Jig".

Also watch for hard sectored diskettes (more than one hole in the mylar
goes by the index hole in the jacket if you manually turn it.)

I don't think that there are any density differences, but single and
double sided diskettes are different. The position of the index hole is

I don't think that there are any density differences, but single and
double sided diskettes are different. I don't remember the difference -

All the same. But watch out that there are a lot of alignment diskettes
extant, and it would be a shame to wipe one of those for routine data

Fred Cisin                      cisin_at_xenosoft.com
XenoSoft                        http://www.xenosoft.com
Received on Wed May 21 2003 - 20:07:01 BST

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