> The question often occurs: What is the difference between the various
> densities since the coating seems to be the same for SD, DD and QD.
[Scott Mueller, Upgrading and repairing PCs, eighth edition, p.554]
5 1/4-Inch 3 1/2-Inch
-----------------------------------------------+-----------------------------
Double Quad High | Double High Extra High
Density Density Density | Density Density Density
Media Parameters (DD) (QD) (HD) | (DD) (HD) (ED)
-----------------------------------------------+-----------------------------
Tracks Per Inch (TPI) 48 96 96 | 135 135 135
Bits Per Inch (BPI) 5,876 5,876 9,646 | 8,717 17,434 34,868
Media Formulation Ferrite Ferrite Cobalt | Cobalt Cobalt Barium
Coercivity (Oersteds) 300 300 600 | 600 720 750
Thickness (Micro-In.) 100 100 50 | 70 40 100
Recording Polarity Horiz. Horiz. Horiz. | Horiz. Horiz. Vert.
-----------------------------------------------+-----------------------------
"Disks have two types of densities: logitudinal density and linear density.
Longitudinal density is indicated by how many tracks can be recorded on the
disk, often expressed as a number of tracks per inch (TPI). Linear density
is the capability of an individual track to store data, often indicated as a
number of bits per inch (BPI). Unfortunately, both types of densities often
are interchanged incorrectly in discussing different disks and drives.
(...)
Both the quad- and DD disks store the same linear data on each track. They
use the same formula for the magnetic coating on the disk, but the
quad-density versions represent a more rigorously tested, higher-quality
disks. The HD disks are entirely different, however."
--
\\//
peter - http://www.softwolves.pp.se/
- and God said: nohup make World >& World.log &
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