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(fdutils.info)Smart use of the dtr

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Smart use of the data transfer rate
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   Due to different drive rotations speeds, 5 1/4 double density disks
and 3 1/2 double density disks are accessed using different raw data
transfer rates (300 kb/s for the faster spinning 5 1/4 disks, and only
250 kb/s for the slower spinning 3 1/2 disks).  The method described in
this section consists in using the faster data transfer rate intended
for 5 1/4 disks on 3 1/2 disks, and thus boost the raw capacity per
track of these disks.  This is possible because 300 kb/s is still low
enough not to excede the specification of the disk surface of a double
density disk (which 500 kb/s would).

   *Usage: this method is only available for 3 1/2 double density
disks.  The disk obtained cannot be booted from by LILO, and are
inaccessible from MS-DOS.*

   The following table shows the media description for a format using
this method in conjuncion with the previous methods:
     density     tot. cap.    throughput    media description
     3 1/2 DD     1120KB         17KB/s     qd tracksize=7KB mss

   We use the `QD' density selector to describe this particular DTR
set-up, although the acronym `QD' is already taken to name 96tpi double
density 5 1/4 disks.  However, as this dtr trickery is only meaningful
for 3 1/2, we hope that there will be no ambiguity.