GNU Info
(fdutils.info)More sectors
More sectors per cylinder
=========================
The official formats used by MS-DOS and other operating systems are
generally very conservative. It is often possible to fit more sectors
on each track than the default by simply reducing the size of the gap
between tracks and/or the size of the leftover space at the end of the
disk.
For example, a 3 1/2 disk has a raw track capacity of around 12500
bytes. The raw capacity of a floppy disk is not rigorously constant
among different boxes, because both the data transfer rate of the floppy
controller, and the rotation speed of the drive are subject to small
variations. In order to account for these, we have to use a safety
margin, and we only use up 12450 bytes of the 12500 bytes that are
theoretically available.
A sector contains a header of 62 bytes and 512 bytes of data. A
minimum gap of about 45 bytes should be used in order to leave enough
time to the floppy controller to "rest" between reading two successive
sectors. In total, 619 bytes per sector are thus needed.
This shows that we can fit 12450 / 619 = 20 sectors per track.
*Usage:* These disks are bootable by Lilo, and can be read in MS-DOS
using numerous shareware utilities such as `vgacopy', or `fdformat' or
many others. Check your nearest Simtel mirror.
With dos6, you don't need any add-on utilities, just put the
following line in your `config.sys':
drivparm=/d:0 /f:7 /h:2 /s:21 /t:82
^ ^ \______________/
| | |
drive number | max geometry
|
drive type, consult the dos help system for details
*Interesting Formats:*
density tot. cap. throughput media description
5 1/4 DD 800KB 30KB/s dd sect=10
3 1/2 DD 800KB 25KB/s dd sect=10
3 1/2 HD 1600KB 50KB/s hd sect=21
3 1/2 ED 3200KB 100KB/s ed sect=42
The `--dd', `--hd' and `--ed' options describe the density of the
media to be formatted (double density, high density or extra density).
The `-s' options describes the number of 512 byte sectors per track.
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