floppy disks -- Technical Information

The COHERENT system lets you read or write to floppy disks, using a variety
of different formats.   You can choose the format that  best suits the task
at hand.

Disks Supported

COHERENT lets you use either 3.5-inch or 5.25-inch disks, in either high or
low density; what you use depends  upon the type of hardware that you have.
The  following table  gives some  commonly used  diskette device  names and
formats.  The  minor number  of each  device is also  given; note  that all
floppy-disk devices have the major number of 4:

Device NameSectors/TrackHeadsSectors BytesFormatMinor Number
/dev/f9a0      9        2    720  360 KB 5.25"     12
/dev/f9a1      9        2    720  360 KB 5.25"     28
/dev/fqa0      9        2   1440  720 KB 3.5"      13
/dev/fqa1      9        2   1440  720 KB 3.5"      29
/dev/fha0     15        2   2400  1.2 MB 5.25"     14
/dev/fha1     15        2   2400  1.2 MB 5.25"     30
/dev/fva0     18        2   2880  1.44 MB3.5"      15
/dev/fva1     18        2   2880  1.44 MB3.5"      31

Device names ending in `0' indicate  drive A:, names ending in `1' indicate
drive B:.  For a  fuller description of COHERENT's floppy-disk devices, see
the Lexicon entry for fd.

MS-DOS Format

COHERENT lets  you read or write  to floppy disks that  contain MS-DOS file
systems.  Both tasks use the commands doscp or doscpdir. These commands are
discussed in full in their respective Lexicon entries.

To  read  files  from an  MS-DOS  disk,  use doscp  with  the  name of  the
appropriate for the floppy-disk device that  you will be using (as given in
the above table).  For example, to copy binary file fred.exe to the current
directory from a low-density, 5.25-inch  MS-DOS floppy disk in drive A, use
the following command:

    doscp /dev/f9a0:fred.exe .

The following command copies to the  current directory all files on a high-
density, 5.25-inch MS-DOS floppy disk in drive B:

    doscp /dev/fha1:\* .

To write a  file to a preformatted MS-DOS floppy  disk, again use the doscp
command, but invert the order of the arguments.  For example, to write file
fred.ms,  which contains  text, to a  low-density, 5.25-inch  MS-DOS floppy
disk in drive A, use the following command:

    doscp -a fred.ms /dev/f9a0:

Note  that the  `a' flag  in  the command  line tells  COHERENT to  convert
linefeeds to  the linefeed/carriage return combination,  as used by MS-DOS.
You will want to use this flag only when transferring text files to or from
an MS-DOS floppy disk.

The following command copies all files  in the current directory to a high-
density, 3.5-inch MS-DOS floppy disk in drive B:

    doscpdir . /dev/fva1:

Note that when you copy a  file to an MS-DOS floppy disk, COHERENT observes
the MS-DOS  file-name conventions: it permits only  eight characters to the
left of the period, and only three characters to the right of it.

(It should  be noted in passing  that you can use the  doscp or doscpdir to
read files  from or write files  to an MS-DOS partition  on your hard disk.
All that  is necessary is  to replace the  name of floppy-disk  device with
that  of the  hard-disk  device for  the  partition in  question.  See  the
Lexicon entry  for at for  a list of  hard-disk devices; see  the entry for
fdisk for information on how to  read the layout of your hard disk; and see
the  entries  for doscp  and  doscpdir  for details  of  how  to use  these
commands.)

Finally, COHERENT lets  you format a floppy disk and  create an MS-DOS file
system on it.  To do so,  you must use the commands fdformat and dosformat.
fdformat is described in detail in its Lexicon article.

To format a high-density, 5.25-inch floppy disk in drive B and write an MS-
DOS file system onto it, use the following commands:

    /etc/fdformat -av /dev/fha1
    dosformat /dev/fha1:

COHERENT Format

If you wish, you can create  a COHERENT file system on a floppy disk, mount
it, and use standard COHERENT commands to manipulate the files on it.  This
illustrates well the fact that to  COHERENT a file system is a file system,
whether it  resides on  a hard,  a floppy disk,  or any  other mass-storage
device.   You can  use such  mountable floppy  disks as  an easy  method of
backing up files, or as a  flexible extension to any other file system that
you have currently mounted.

To  create a  COHERENT  file system  on  a floppy  disk, you  must use  the
commands fdformat and mkfs.  Each is described in detail in its own Lexicon
article.  The  following example creates a COHERENT file  system on a high-
density, 3.5-inch floppy disk placed in drive B:

    /etc/fdformat -av /dev/rfva1
    /etc/mkfs /dev/fva1 2880

In this example, command fdformat  formatted the disk.  The option -v tells
fdformat to use its verification mode.  This takes longer, but ensures that
the disk is good.  If this command fails, it means that the floppy disk has
a bad block or sector: throw it away and try again.

Command mkfs  builds a COHERENT file  system on the disk.   The file system
has  2,880 blocks  (1.44 megabytes)  of space, which  is appropriate  for a
high-density, 3.5-inch floppy disk.

Now that the file system is  created on the disk, you must mount it.  To do
so, use  the script mount;  this is described  in its Lexicon  entry.  This
mounts the file system on directory  /f0 if the disk drive is drive 0 (A:);
or f1 if the disk drive is drive 1 (B:).

While it  is customary to mount  file systems under directory  `/', you are
not required to  do it.  For example, if your  login identifier is fred and
your  home directory  is /usr/fred,  you can mount  the floppy  disk's file
system onto  a subdirectory of  /usr/fred and so  make the floppy  disk, in
effect,  an extension  of your  home  directory.  To  mount a  floppy on  a
directory other than its default, use the command /etc/mount. The following
command does this for the 3.5-inch disk we formatted in the above example:

    /etc/mount /dev/fva1 /usr/fred/temp

Now, all files you copy  into directory /usr/fred/temp using the cp command
will be written  directly onto the floppy disk.  Note  that you may need to
log in as the superuser root  and use the command chown to ensure that fred
owns the  file system on that  floppy disk.  For details  on chown, see its
entry in  the Lexicon.  For  details on shorthand notations  for mount, see
its entry in the Lexicon.

One  important  point about  mounting  file systems:  before  you remove  a
COHERENT-formatted  floppy disk  from  its drive,  you must  first use  the
command /etc/umount  to unmount its file  system.  If you do  not, all data
that COHERENT  has stored in its  buffers will not be  written to the disk,
and may be lost.  Worse, if you remove one COHERENT disk and insert another
without unmounting  the old  disk and mounting  the new one,  COHERENT will
write all  data in its  buffers onto the  new disk without  regard for what
that disk contains;  in all likelihood, this will trash  the file system on
the new  disk and render  its data unreadable.   So, the lesson  is: always
unmount a floppy disk before you remove it!.  To unmount the floppy disk we
used in our previous example, use the command:

    /etc/umount /dev/fva1

By the way, that's not a misprint: the command is umount, not ``unmount''.

Finally, please note  that you can mount only a  COHERENT file system.  You
cannot  mount  a file  system  created  with MS-DOS,  XENIX,  or any  other
operating system.

You  can,  however import  a  set  of files  --  including their  directory
structure --  from UNIX, XENIX, or any other  UNIX-like operating system by
using the  utilities.  cpio or tar.  Each of these utilities  uses a backup
algorithm that  is implemented on many operating  systems.  To import files
from another operating  system, go to the machine that  holds the files you
want and use its version of cpio or tar to back up the files or directories
to a  set of floppy disks  or cartridge tape.  Then  bring the floppy disks
back to  your COHERENT system and use COHERENT's  implementation of cpio to
read the  back-up disks.  The following section gives  directions on how to
do this; or see the Lexicon entries for cpio and tar for more information.

Raw Format

Finally, COHERENT lets  you use floppy disks in their  raw form as a backup
medium, much as you would use magnetic tape on a larger computer.  You must
first use the command /etc/fdformat with the -v option to format the floppy
disks you will  be using; it is also wise  to label and number the disks so
you  can keep  them in  some  reasonable order.   Then you  can use  any of
COHERENT's archiving utilities, such as tar or cpio, to archive directories
or entire file systems onto the disks.  It is recommended that you format a
generous supply of floppy disks before you begin; if you run short of disks
while archiving your files, you will  have to abort, format more disks, and
begin again.  For  details on how to use the  archiving programs, see their
respective entries in the Lexicon.

Interleave

The ``interleave'' of a disk device refers to the pattern with which blocks
are scattered around a disk cylinder.   It can have a drastic effect on the
speed with which data are read from and written to a disk.

The interleave  is set by  the file system  written onto that  disk.  Thus,
under COHERENT the interleave is  set by the command /etc/mkfs. By default,
this  command  sets the  interleave  pattern  to six.   You  can request  a
different interleave  pattern; however, the proper  interleave for a floppy
disk can  vary wildly, depending upon  what disk drives you  have, your CPU
speed,  amount  of RAM,  and  several  other variables.   The  best way  to
discover the interleave pattern is to experiment.

The following script, by Fred Smith (fredex%fcshome@merk.merk.com), formats
a floppy disk  to a specified set of factors,  generates a file system, and
runs a  program to exercise it.   By running this program  with a number of
different settings, you  can find which is best for  your system.  You will
find  this to  be especially  helpful  if you  work frequently  with floppy
disks:

# usage: doit <interleave> <skew> <device name> <tracks (not sectors) per drive>
#   for a 3.5dshd in drive 1:  sh doit 3 6 fva1 2880
#   for a 5.25dshd in drive 0: sh doit 3 6 fha0 2400
# assumes that iozone is in the current directory, and that there is a
# subdirectory named 'test', over which the floppy can be mounted.

echo /etc/fdformat -a -i $1 -o $2 /dev/r$3
/etc/fdformat -a -i $1 -o $2 /dev/r$3
/etc/badscan -v -o flop /dev/$3 $4

# in case you want to modify the permissions of the new file system.
# if you don't want to do the vi, then run this as root.
#vi flop

    /etc/mkfs /dev/$3 flop
    /etc/mount /dev/$3 ./test
    cd test
    ../iozone
    cd ..
    /etc/umount /dev/$3

Debugging Floppy-Disk Problems

The  COHERENT  floppy-disk  driver has  been  used  frequently  by tens  of
thousands of users over a number  of years, and has been found to be sound.
However, from time  to time a problem can arise.   This usually occurs when
users install  new equipment  into their  systems.  If you  continually see
error messages  that indicate a  problem with the  floppy-disk drive, e.g.,
door open, try the following steps to diagnose the problem:

1. Is CMOS configured for the floppy-disk drives?  The CMOS on your machine
   may have  been ``clobbered''  by an  event that has  nothing to  do with
   COHERENT -- e.g., a power surge.

   To check your CMOS, you can  reboot your system; the BIOS on practically
   every computer  includes a program  for reading and  resetting the CMOS.
   Or, you can read the output  of device /dev/cmos. The Lexicon entry cmos
   describes how to interpret the output of this device.

2. If  you have  switched hard  drives, did you  change IDE  controllers or
   alter  any jumpers?   If the  same  card controls  both floppy  and hard
   drives, you  may have moved a  jumper wrongly.  It may  also be that the
   new controller has a bug.

3. Try  using  the  command /etc/conf/bin/idtune  to  change  the value  of
   variable FL_DSK_CH_PROB;  then use the  command /etc/conf/bin/idmkcoh to
   link a new kernel, and boot  the new kernel.  To check the current value
   of that  variable (or of  any tunable variable), use  the command idtune
   -p.

4. Is any other equipment conflicting with the drive in question, such as a
   QIC-80 or  QIC-40 tape drive?   Try pulling the device  in question, and
   see if that makes the problem go away.

5. Check that all cables are secure and all cards seated properly.  If your
   machine is  loaded with equipment, its  interior can be a  rat's nest of
   cables and connectors; and while installing new equipment, it is easy to
   loosen a cable or jar a card so that it no longer works.

6. Try the  following command with a  floppy disk in place,  just after you
   have booted COHERENT and before any other access to the drive:

       dd if=/dev/rdev of=/dev/null count=2 bs=30b

   dev is  names the  floppy-disk device in  question, e.g., fha0  or fva1.
   This command  may help  if the driver  is not getting  the recalibration
   status it expects.

7. If all else fails, try swapping  out the controller or drive.  It may be
   that the device simply has failed.

See Also

Administering COHERENT,
badscan,
cpio,
doscp,
doscpdir,
dosformat,
fd,
fdformat,
gtar,
mkfs,
mount,
umount

Notes

You can create a version of  the COHERENT operating system that runs from a
floppy disk.   Such a  version of  COHERENT can be  used to create  test or
backup systems for device drivers or other applications.  For directions on
how to  make a version of  COHERENT that boots from a  floppy disk, see the
Lexicon entry booting.

© 2012 by Stephen A. Ness