Floppy drives

[Wolf N. Paul]

In article <582 at mccc.UUCP> pjh at mccc.UUCP (Pete Holsberg) writes:
>
>In looking through /dev for diskette device files, I came across a
>puzzling set of directory listings.  For example, for the device 1,0, I
>can find no less than 13 different entries with 6 different names and 3
>different link counts!  Here they are (number of links in parens):
>
>/dev/SA:   diskette (1), f0q15dt (5)
>/dev/rSA:  diskette (1), f0q15dt (6 !!)
>/dev/dsk:  0s24 (5),     f0q15dt (5 !!), fd (5),    fd096 (5)
>/dev/rdsk: 0s24 (6 !!),  f0q15dt (6 !!), fd (6 !!), fd096 (6 !!)
>/dev/dos:  A (6)
>
>Can someone explain this?

Yes! One of the nice things about UNIX is multiple links to the same
inode (i.e. file or device). This allows one to call the same file different
names, depending on which application wants to access it, or what purpose
it is to be used for.

In the list above, the following names are all links to the same device,
namely the raw interface to the first floppy drive:

/dev/rdsk/fd, /dev/rdsk/f0q15dt, /dev/rdsk/fd096, /dev/rdsk/0s24, dev/dos/A,
and /dev/rSA/f0q15dt.

The devices in /dev/SA and /dev/dsk should have a different major number
from the ones in rSA and rdsk, but are otherwise identical.

Some of these names are required by different programs; for example, the
DOS file access programs (doscat, doscp, dosdir) need the /dev/dos/A entry.
Others are simply different naming conventions indicating what the capacity
of that particular device is (i.e., fd096 indicates a 96 tpi disk drive, 
f0q15dt indicates a quad density (96tpi) device formatted with 15 sectors
doublesided, etc.). Some systems (i.e. V/AT) also link the first floppy
in it's high capacity version to /dev/rmt/mt0, or /dev/tar, as the default
device for tar(1), since such systems often have no actual tape drive.

On my system, I have added /dev/dos/a, so I don't have to capitalize the
drive letter when using the dos commands, as well as special mnemonic
names for my two floppies in their various modes (these exist both in /dev/dsk
and in /dev/rdsk):

fd0dd	# Drive 0, Double Density (360K)
fd0qd	# Drive 0, Quad Density (720K -- a better use of DS/DD disks)
fd0hd	# Drive 0, High Density (1.2M -- the standard AT format)

fd1qd	# Drive 1, Quad Density (3.5", 720K)
fd1xd	# Drive 1, eXtra Density (3.5", 1.44MB)

I do not know what the /dev/SA and /dev/rSA directories on V/386 are,
but would guess that they are for the use of some System Administration
utility.

As to the 720K drive entries, on V/AT they are as follows (Maybe
someone knowledgable on V/386 could confirm these numbers or else
provide more accurate ones):

Raw devices:

Drive 0, 5.25" 720K ......... Major 6, Minor 87
Drive 0, 3.5"  720K ......... Major 6, Minor 119
Drive 0, 3.5"  1.44M ........ Major 6, Minor 102

Drive 1, 5.25" 720K ......... Major 6, Minor 95
Drive 1, 3.5"  720K ......... Major 6, Minor 127
Drive 1, 3.5"  1.44M ........ Major 6, Minor 110

Block Devices:

Drive 0, 5.25" 720K ......... Major 1, Minor 87
Drive 0, 3.5"  720K ......... Major 1, Minor 119
Drive 0, 3.5"  1.44M ........ Major 1, Minor 102

Drive 1, 5.25" 720K ......... Major 1, Minor 95
Drive 1, 3.5"  720K ......... Major 1, Minor 127
Drive 1, 3.5"  1.44M ........ Major 1, Minor 110

You can just "mknod" these devices with these numbers, and whatever
names you feel comfortable with. 

And by the way, Pete, would you let me know by email what the status of
Larry Gensch's XCOMM is? When is his next version coming out?
What does one hear on CIS on that subject?

Wolf
-- 
Wolf N. Paul * 3387 Sam Rayburn Run * Carrollton TX 75007 * (214) 306-9101
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