FD(HW) XENIX System V FD(HW)
Name
fd - floppy devices
Description
The fd devices implement the interface with floppy disk
drives. 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 512 bytes at a time using
raw i/o. Note that block transfers are always a multiple of
the 1K disk block size.
The floppy devices are named /dev/fd0 and /dev/fd1 (see
Notes, below, for more information about device naming
procedure).
The corresponding character special (raw) devices, /dev/rfd0
and /dev/rfd1, 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).
Files
/dev/fd0 /dev/rfd048ds8 /dev/rfd096ds15
/dev/fd1 /dev/rfd148ds8 /dev/rfd196ds15
/dev/rfd0 /dev/rfd048ds9 /dev/rfd096ds8
/dev/rfd1 /dev/rfd148ds9 /dev/rfd196ds8
/dev/rfd048ss8
/dev/rfd148ss9
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 512 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)
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FD(HW) XENIX System V FD(HW)
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 |
| ds/8 ds/9 ss/8 ss/9| ds/15 ds/8|
|______|__________________________________________|
| Drive| Minor Device Number |
|______|______|______|______|______|_______|______|
| 0 | 12 | 4 | 8 | 0 | 52 | 44 |
| 1 | 13 | 5 | 9 | 1 | 53 | 45 |
| 2 | 14 | 6 | 10 | 2 | 54 | 46 |
| 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 | ds - 1 | |
|__________|_______________________|___________|_______________________|
| 32 | 16 8 | 4 | 2 1 |
|__________|___________|___________|___________|___________|___________|
| 0 | 0 | 1 | 0 | 0 | 0 |
| | | | | | |
|__________|___________|___________|___________|___________|___________|
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FD(HW) XENIX System V FD(HW)
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 |
|___|___|_____________|
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.
It is not advisable to format a low density (48tpi) diskette
on a high density (96tpi) 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.
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