Different disk types (was: Re: CBM 8280)

From: peter karlsson (pk_at_mds.mdh.se)
Date: 1999-09-01 11:11:09

> 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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