Jochen Kunz wrote:
On 2003.05.29
20:27 Jerome H. Fine wrote:
John, if you are reading this, it would be best if you could
confirm - also even better if you could explain why they
hardware to read the DEC RX02 8" floppy media is
not available on a PC.
I am not John, but this may be the explanation:
The RX02 uses double density only for the data inside the sector. The
sector header is (mostly) the same as a RX01 sector header and it is
rcorded in single density. Result: A RX01 holds 128 Bytes per sector, a
RX02 holds 256 bytes per sector, thus doubling the capacity. So the
floppy controller has to switch the data rate from sector header to
sector data... A really, uhhm, "interresting" design.
tsch??,
Jochen
Homepage:
http://www.unixag-kl.fh-kl.de/~jkunz/
Jerome Fine replies:
YES!!!
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.
On the other hand, in my experience, in some cases the floppy
media can be "somewhat" damaged. Under some circumstances,
is is possible to use the RT-11 FORMAT command to restore
those bad sectors so that they function correctly. Of course,
if the LLF is totally wiped out for any given sector, I guess that
nothing can be done. Warning - if the FORMAT command
is used, all current information on the floppy is destroyed - save
anything that is still useful BEFORE the FORMAT command.
NOTE that most 3rd party RX01/RX02 controller/drive pairs
for DEC PDP-11 hardware were able to do the complete
LLF for RX01/RX02 media. In fact, I seem to remember that
the controller was not required - the drive contained the ability
to do a LLF off-line. This was not the RT-11 FORMAT
command, but a complete LLF.
The same situation occurred with the DEC RX50 floppy media.
The DEC RX50 drive could NOT perform an LLF.
However, by the time that DEC allowed the RX33 on the RQDX3,
DEC had switched to industry standard HD PC 1.2 MByte floppy
drives and media with 2400 blocks. The first time I used RT-11
to perform a FORMAT command on an industry standard
UNFORMATTED PC HD 1.2 MByte floppy, AND IT
WORKED, I think I almost fainted I was so shocked.
The question that is still unanswered is IF the board that dbit
has available that supports the RX01 floppy media on a PC
with the appropriate 8" floppy drive CAN ALSO support
an RX02 media? I seem to remember that the answer is NO!
But perhaps John can confirm this answer?
Sincerely yours,
Jerome Fine
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