17 Extended floppy densities

Contents of this section

The extended floppy densities are called xd (extended double) and xh (extended high). They fit more data on a floppy by going outside the `factory specifications' of the floppies and drives. For example, on 3.5" DD floppies, the normal d (double) density format uses 80 tracks and 9 sectors per track, the xd format uses 82 tracks and 10 sectors per track, which fits 820 Kb. on the floppy.

Tbackup needs the setfdprm program to use extended densities. I have no idea when this program first appeared in Linux, so you may not have it.

Not all floppies and/or floppy drives are able to go outside their `factory specifications' and hold extra data. For example, my 5.25" drive can't read and write xd density. Most modern 3.5" HD drives however have no problems reading and writing extended densities.

To find out which extended densities your drives support, just experiment with tbackup and trestore.

Due to limitations in the Linux kernel, reading and writing 1.7 Mb. on 3.5" HD floppies is extremely slow (some 8 times slower as normal floppy access) Note: This was written in 1994, the limitation may be gone by now. This makes the xd density for 3.5" floppies virtually useless. There seems to be some non trivial patch needed to the Linux kernel to allow fast writing of the 3.5" xd format.

Currently you can not use the xd density if you have a DD floppy drive, you can only use xd and xh on a HD drive. I haven't found the xd formatting parameters needed for DD drives, if you have them please let me know.

17.1 extended densities under MS-DOS

If you are actually going to make backups with extended densities, make sure that you have access to at least one other machine that supports them. This other computer need not be a Linux machine, there are also MS-DOS packages that support extended densities. I have one called fdformat, archive name FDFORM17.ZIP.

17.2 using extended densities under Linux

If you want to read or write extended density floppies under Linux outside tbackup, you will have to edit some configuration files first.

Before accessing an extended density floppy, type the command

setfdprm -p /dev/fdnr name
where nr is the floppy drive number, 0 or 1, and name is Now you can use mdir a: or mdir b: and other mtools commands to access the floppy.

You can also mount it with

mount -t msdos /dev/fdnr mountpoint
Formatting is possible with
fdformat -n /dev/fdnr

where the -n option switches off the verify pass as verification of extended floppy formats won't work with the current version of fdformat. You can do a simple verify by hand by typing

cp /dev/fdnr /dev/null
and looking if cp gives an error.

If you are finished with the floppy, you sometimes may have to type

setfdprm -c /dev/fdnr
to get the drive back in `autodetect mode' so that it will accept normal floppies again.

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