Floppy format

[Floyd Davidson]

In article <1991Mar6.001518.15066 at ra.src.umd.edu> zafar at phoenix.src.umd.edu (Sohail Zafar) writes:
>Hi everyone,
>	I have a question about formating floppies on unixpc. First I don't
>know the difference between /dev/rfp020 and /dev/rfp021.  Secondly, I

Disks, either the floppy or the hard drive, are divided into slices
(or call them partitions, or call them volumes, whatever).  On the
UnixPc all disk devices have the same major device numbers (one for the
block device, and another for the raw device).  There can be up to 16
slices on a single disk.  The device driver selects which disk and
which partition you are addressing by looking at the minor device
number.  Each /dev/rfp0nn (and each /dev/fp0nn) file is for a different
minor device number.  00n is on the first hard disk, 01n is on the
second hard disk, and 02n is on the floppy.

So /dev/rfp020 is the "raw" access to slice 0 of the floppy, and
/dev/rfp021 is slice 1.

And if you have some strange desire to experiment, it is possible to
format and access the rest of the slices (2, 3, etc).  There just
isn't any useful purpose in doing so that I know of.

Normally slice 0 is set up to be only the first cylinder on a disk and
contains the Volume Home Block (information about the disk), the boot
loader, and a bad block table if it is a hard disk.  Slice 0 can also
be used to access the entire disk because it starts at the first track,
and if you ignore the partition table...

Slice 0 is not a mountable partition, but any other partition can have
a file system built on it.

>cannot format a 360K or a 720K floppy because both have 9 sectors per
>track and iv sends a message "iv: not slice 0 of the raw device".  I
>used both fformat and also fffc but no luck. iv will not take 9 sectors.

The trick is to format for 10 sectors.  On the UnixPc the difference
between a hard disk (17 sectors) and a floppy disk, is one has an
odd number of sectors and the other (the floppy) has an even number.
I've never used the msdos floppy tools, but they use disks formatted
for 10 sectors and then ignore the last one (or at least that is what
I understand).
 
>The third question is that can you use a floppy formatted on a spark
>station where the device is /dev/rfd0c.  What I mean to say is that
>if I can use cpio on /dev/rfd0c on my university sun I won't have to
>wait forever to load using kermit. Is there a way or not?  I have
>tried but without any luck.  Floppies formatted on unixpc are recognized
>on Sun (I can cpio and tar) but any floppy formatted on Sun is not
>recognized by unixpc nor is any information written by Sun on a diskette
>formatted on the pc itself.  I was wondering if anyone had any idea as
>to how to use a floppy on both Sun and unixpc.  What I think is because
>of the 9 sectors per track problem.

Could be just the 9 sectors, but there are probably a lot of other
differences too.  Tar and cpio (and pax) do raw read/writes to the
disk.  They don't use a file system on the disk.  To copy files to
the disk on one machine and read them on another machine will require
a lot more compatibility than is required by the archive programs.

Floyd
-- 
Floyd L. Davidson  |  floyd at ims.alaska.edu   |  Alascom, Inc. pays me
Salcha, AK 99714   |    Univ. of Alaska      |  but not for opinions.