Date : Sat, 12 Sep 1992 02:52:06 GMT
From : rde!ksmith!keith@uunet.uu.net (Keith Smith)
Subject: Re: 720K 5-1/4" diskettes
In article <".9-Sep-92..9:31:25.EDT".*.Michael_D._Sprague.wbst311@Xerox.com>
Sprague.Wbst311@xerox.com writes:
>
>Just to be nit-picky :-) 720K 5-1/4" drives/disks are NOT quad density,
>though they are sometimes incorrectly called that!! The drives/disks are
>DOUBLE DENSITY, but have twice as many TRACKS as a standard Double Density
>drive/disk.
>
> ~ Mike (sprague.wbst311@xerox.com)
Hmm, So let's get this straight. They are double track and double
density. 2 * 2 = 4. 4 times the density is NOT QUAD density. Got it.
To pick a nit ....
The org CP/M disks I had were 10 hole hard sectors with 100K per side on
a single sided disk, basically DS/QD is 7+ times that. The issue at
hand is DENSITY however. Density meaning how tight the bits are packed.
Tightly packing the sectors and increasing their size to 512 bytes
enabled us to get 180K on the side of a disk rather than the old 100K
functionality. This basically put the "bits" almost twice as close
together on a given track, hence "double" density. Doubling the number
of tracks brings the bits another factor of 2 closer together hence the
term "QUAD DENSITY" diskettes. QD diskettes were marketed extensively
pre-ibm and clone takeover for hardware such as EPSON, OLIVETTI, SEIKO
(Yea The watch guys sold computers!) and my Heathkit. The AT&T 3B2 used
these puppies too. Now the quality of standard IBM "Double Density"
360K media is so good it will work fine as 720K "Quad Density" too.
The Current Crop of AT/HD stuff is even higher than quad, packing 15 512
byte sectors on a track instead of 9 a factor of 1.7 improvement in
density. The 3.5" disks on the other hand STARTED at 720K which was
called "double density" so the 1440K 18 SPT 3.5's are now often called
"quad density" which is where the confusion may be from.
The REAL density improvement on 5.25" has not "really" doubled though.
Single Density = 100K per side
Double Density = 180K per side really 1.8 density not 2
Quad Density = 360K per side really 3.6 density but advertising you know.
High Density = 600K per side They didn't push to "HEPT" density on
this one :)
Again this is BIT density, nothing to do with actual storage mind you.
Also the 3.5's really started out on the HD emulsions. Now the NEW
stuff comming out is pushing 10MB on Standard floppy style media. They
stopped "densitizing" the names (finally, thank god) and just say
"2.4MB" or "5MB" 5-1/4" media.
--
Keith Smith uunet!ksmith!keith 5719 Archer Rd.
Digital Designs BBS 1-919-423-4216 Hope Mills, NC 28348-2201
Somewhere in the Styx of North Carolina ...