30 May
2003
30 May
'03
9:17 a.m.
Megan wrote:
So when under
the command in RT-11:
FORMAT DY0:/SINGLE
all that happens is that the density bit in the sector header is set
to "Single Density", but a complete LLF (Low Level Format)
is not done, in fact can't be done, using a DEC RX02 drive.
Likewise, the RT-11 command:
FORMAT DY0:/DOUBLE (the default)
sets the density bit in the sector header to "Double Density"
and again can't be done with a DEC RX02 unless the floppy
media is already LLF.
If you have a DSD disk unit with a floppy, that will truly
format the floppy. The only disk drive/system from DEC
which could format a floppy is the PDT-11/150 (!) This was discussed at some length on a DEC-interal
mailing
list following the sale of PDTs to employees. It turns out
that the PDT writes all the formatting info for any track it
writes, so if you write to the entire disk, it will be
formatted single density.
Please confirm that the PDT-11/150 uses ONLY RX01 media.
ALSO, is the device driver for the PDT-11/150 the PD.SYS
file? I seem to remember that the PDT-11/150 did NOT have
a hard drive, is that true? If the PDT-11/150 does have a
hard drive, which hard drive and what is the name of the file
for the device driver?
You can then take the disk to another drive (RX02) and
change
the density to double.
That was the essence of my reply above with the two different
commands under RT-11 using a DEC RX02 floppy drive.
What would be helpful is is you would confirm (or deny - since
I am always making mistakes) that the FORMAT command
under RT-11 for 8" floppy media on a Qbus/Unibus system
ONLY sets the density bit in the sector header of the media.
BUT, before that can be done, a successful LLF must occur
with that media.
The DSD 3rd party floppy drives were one method.
You have confirmed that a PDT-11/150 is a second method.
At one point when I had an office on ML5-5 at DEC, I
had a
floppy which was held to a filing cabinet by a large disk
magnet. When people wanted proof, I would take it down and
demonstrate it as being unreadable, then would format it in
a PDT-11/150 I had, and then proceed to use it...
While I have no doubt that the PDT-11/150 can do an LLF
on an 8" floppy media and your demonstration was evidence
of that fact, I do not agree that it was proof. I have, on many
occasions, had an 8" floppy which I could not read on a
DEC RX02. It had already had an LLF, but all attempts
to read the media were unsuccessful or unreadable. On a
Qbus PDP-11/23 with a DEC RX02 drive, I used the
RT-11 command:
FORMAT DY0:
and it was successful and I could again read the 8" media.
So while the magnet would likely do a bulk erase, it is not
proof that it was done and that an LLF was required - yes
99.9% of the time I would agree it would be necessary, but
very rarely it might not.
The same
situation occurred with the DEC RX50 floppy media.
The DEC RX50 drive could NOT perform an LLF.
There was, however, a ROM which was
available (at least I had
one at one point) which allowed formatting of RX50 media on
a PRO series machine...