FD(HW) UNIX System V
Name
fd - floppy devices
Description
The fd devices implement the interface with floppy disk
drives. Each device name corresponds to a specific major
and minor device. Typically, the tar(C), cpio(C) or dd(C)
commands are used to read or write floppy disks. For
instance,
tar tvf /dev/fd0
tabulates the contents of the floppy disk in drive 0 (zero).
The block special fd devices are also block-buffered. The
floppy driver can read or write 1K bytes at a time using raw
i/o. Note that block transfers are always a multiple of the
1K disk block size.
XENIX Devices
XENIX diskette device file names use the following format:
/dev/[r]fd[0,1][48ss8,48ss9,
96ds9,96ds15,135ds9,135ds18]
(See Notes, below, for more information about device naming
procedure.) The corresponding character special (raw)
devices afford direct, unbuffered transmission between the
floppy and the user's read or write transfer address in the
user's program.
For information about formatting, see format(C).
The minor device number determines what kind of physical
device is attached to each device file (see Notes). When
accessing the character special floppy devices, the user's
buffer must begin on a word boundary. The count in a
read(S), write(S), or lseek(S) call to a character special
floppy device must be a multiple of 1K bytes.
Device names determine the particular drive and media
configuration. The device names have the form:
fd048ds9
Where:
fd0 = drive number (0, 1, 2 or 3)
48 = number of disk tracks per inch (48 or 96)
ds = single or double sided floppy (ss or ds)
9 = number of sectors on the floppy (8 or 9)
For instance, /dev/fd048ss9 indicates a 48 track per inch,
single sided, 9 sector floppy disk device in drive 0.
The minor device numbers for floppy drives depend on the
drive and media configuration. The most common are:
_________________________________________________________________
| 48tpi | 96tpi | 135tpi |
| ds/8 ds/9 ss/8 ss/9 | ds/15 ds/8 | ds/9 ds/18 |
|________________________________________________________________|
|Drive | Minor Device Number |
|_____|_________________________________________________________|
| 0 | 12 | 4 | 8 | 0 | 52 | 44 | 36 | 60 |
| 1 | 13 | 5 | 9 | 1 | 53 | 45 | 37 | 61 |
| 2 | 14 | 6 | 10 | 2 | 54 | 46 | 38 | 62 |
| 3* | | | | | | | | |
| | | | | | | | | |
|______|_____|_____|______|______|_______|______|______|______|
* reserved for special, non-floppy devices connected to
the floppy controller as unit #3.
The scheme for creating minor device numbers is as follows.
When interpreted as a binary number, each bit of the minor
device number represents some aspect of the device/media
configuration.
For example, the minor device number for /dev/fd048ss8 is
``8.'' Interpreted as a binary number, 8 is:
00001000
This is how each bit, or binary digit, is significant:
________________________________________________
|48tpi - 0 | Sectors per | ss - 0 | Drive |
|___________| |________| |
|96tpi - 1 | Track | | |
|___________| | | |
|135tpi - 1 | | ds - 1 | |
|___________|_________________|________|_______|
| 32 | 16 8 | 4 | 2 1 |
|___________|_________________|________|_______|
| 0 | 0 | 1 | 0 | 0 | 0 |
| | | | | | |
|___________|________|________|________|___|___|
Only the last six digits of the number are used in minor
device identification. The first significant digit is the
third from the left. In this example, the third digit from
the left is zero, thus the device is 48tpi. The next two
digits mean:
______________________
| | Sectors per |
| Bits | Track |
|_______| |
|16 | 8 | |
|__|___|_____________|
|0 | 0 | 9 |
|0 | 1 | 8 |
|1 | 0 | 15 |
|1 | 1 | 18 |
|___|___|____________|
The fourth digit tells whether the floppy is single sided
(ss - 0) or double sided (ds - 1). The last two signify the
drive number:
________________
| | Drive |
|Bits | Number |
|______| |
|2 | 1 | |
|_|___|________|
|0 | 0 | 0 |
|0 | 1 | 1 |
|1 | 0 | 2 |
|1 | 1 | 3* |
|_|___|________|
* reserved for special, non-floppy devices connected to
the floppy controller as unit #3.
Using this information, you can construct any minor device
numbers you need.
UNIX Devices
UNIX diskette device file names use the following format:
/dev/[r]dsk/f[0,1][5h,5d9,
5d8,5d4,5d16,5q,3h,3d][t,u]
where r indicates a raw (character) interface to the
diskette, rdsk selects the raw device interface and dsk
selects the block device interface. 0 or 1 selects the drive
to be accessed: f0 selects floppy drive 0, while f1 selects
drive 1. The following list describes the format to be
interacted with:
5h 5.25" high density diskette (1.2MB).
5d9 5.25" double density diskette, 9 sectors per
track (360KB).
5d8 5.25" double density diskette, 8 sectors per
track (320KB).
5d4 5.25" double density diskette, 4 sectors per
track (320KB).
5d16 5.25" double density diskette, 16 sectors per
track (320KB).
5q 5.25" quad density diskette (720KB).
3h 3.50" high density diskette (1.44MB).
3d 3.50" double density diskette (720KB).
Format specification is mandatory when opening the device
for formatting. However, when accessing a floppy disk for
other operations (read and write), the format specification
field can be omitted. In this case, the floppy disk driver
will automatically determine the format previously
established on the diskette and then perform the requested
operation (for example, cpio -itv</dev/rsdk/f1).
The last parameter, t or u, selects the partition to be
accessed. t represents the whole diskette. Without t or u
specified, the whole diskette except cylinder 0 will be
selected. u represents the whole diskette except track 0 of
cylinder 0.
Besides the device file naming convention described above,
some of the formats have alias names that correlate to
previous releases. The following list describes the formats
that have an alias:
format alias
5h q15d
5d8 d8d
5d9 d9d
For example, the device file /dev/rdsk/f0q15dt is equivalent
to /dev/rdsk/f05ht.
Files
XENIX Devices:
/dev/[r]fd0 /dev/[r]fd048ds9 /dev/[r]fd196ds9
/dev/[r]fd1 /dev/[r]fd096ds9 /dev/[r]fd1135ds18
/dev/[r]fd048 /dev/[r]fd0135ds18 /dev/[r]fd096ds15
/dev/[r]fd148 /dev/[r]fd148ds9 /dev/[r]fd196ds15
/dev/[r]fd048ds8 /dev/[r]fd048ss9 /dev/[r]fd0135ds9
/dev/[r]fd148ds8 /dev/[r]fd148ss9 /dev/[r]fd1135ds9
/dev/[r]fd048ss8 /dev/[r]fd096
/dev/[r]fd148ss8 /dev/[r]fd196
UNIX Devices:
/dev/[r]dsk/f0 /dev/[r]dsk/f05d8t /dev/[r]dsk/f03h
/dev/[r]dsk/f0t /dev/[r]dsk/f05d4 /dev/[r]dsk/f03ht
/dev/[r]dsk/f05h /dev/[r]dsk/f05d4t /dev/[r]dsk/f03d
/dev/[r]dsk/f05ht /dev/[r]dsk/f05d16 /dev/[r]dsk/f03dt
/dev/[r]dsk/f05d9 /dev/[r]dsk/f05d16t
/dev/[r]dsk/f05d9t /dev/[r]dsk/f05q
/dev/[r]dsk/f0fd8 /dev/[r]dsk/f05qt
Notes
It is not advisable to format a low density (48tpi) diskette
on a high density (96tpi or 135tpi) floppy drive. Low
density diskettes written on a high density drive should be
read on high density drives. They may or may not be readable
on a low density drive.
Use error-free floppy disks for best results on reading and
writing.
(printed 8/30/89) FD(HW)