21 Sep
2015
21 Sep
'15
9:43 a.m.
On 2015-09-21 18:29, Jerome H. Fine wrote:
I am not sure that I understand your suggestion.
While I agree
that the RX02 was able to switch a single-density floppy to a
double-density floppy (and visa versa), the difficulty, as you
pointed out, was performing the initial LLF (Low Level
Formatting) in the first place on Un-Formatted 8" floppies.
That may have been easy with IBM hardware, but DEC
made that impossible if all the user had was a DEC system.
Agreed. The DEC RX01 and RX02 drives could not do a low level format.
But your comment above suggested you needed to find some special drive
and controller combo which supported RX02 floppies, which would just be
irrelevant. If you could format the floppy anywhere, to just IBM SSSD
format, then you were good.
The RX02 special stuff is something you then did on an RX02.
If it was possible to perform a LLF using the same RX50 drive
on
the Rainbow, what was the reason why an LLF could not also be
performed on a PDP-11? There seems to be a number of possibilities:
(a) There was some hardware that the Rainbow had which was missing
on the PDP-11 systems
No.
I don't know how to respond since different individuals will
interpret your story in the opposite manner, So I will add
my own experience when I used the RX02 drive from DEC
along with the DSD RX03 floppy drive.
Around 1990 after I had acquired the DSD RX03 floppy
drive in a DSD 880/30 system, I also managed to acquire
many brands of 8" floppy media. At that point, I had not
yet managed to acquire any tape hardware such as the TK25
which supported a 32 MB disk image, so the floppies were
my primary backup. I probably had about a dozen different
brands of 8" floppies that required an LLF before they could
be used. And since a double-density, double-sided 8" floppy
media held about 1 MB (1976 blocks) as opposed to about
1/2 MB (988 blocks) for double-density, single-sided media,
I set set about the task of enhancing the DEC DY.MAC RX02
device driver after I found the code in V04.00 of RT-11 which
included support for double-sided media.
What may be called "interesting" was that DEC had removed
all of that optional code in DY.MAC by the time V05.00 of
RT-11 was released. That might have had something to do
with the fact that DEC never sold (that I heard of) an RX03
drive.
In any case, adding and correcting the extra code was quite
easy. The challenge was to also add support for a user buffer
being above the 1/4 MB boundary in a PDP-11 with all 4 MB
of memory when a Mapped RT-11 Monitor was used since
the controller supported only 18-bit addresses.
This would be the Qbus controller. And that is an annoying detail, yes.
You need a bounce buffer in the low part of memory. One of a few Qbus
controllers with 18-bit addressing for DMA.
Rod Smallwood
wrote:
On
21/09/2015 10:30, Johnny Billquist wrote:
On
2015-09-21 02:11, Jerome H. Fine wrote:
You bring up a VERY notable lack of support by
DEC of that
situation!!!!!!!!!!!!!!!!!!!!!!
For both the DEC RX01 and the DEC RX02 8" floppy drives,
while it might have been possible that DEC engineers were unable
to initially figure out how to allow users to perform an LLF (Low
Level Format) on the 8" floppy drives, it seems certain that after
3rd party manufactures figured out, DEC could also have supported
that function as well.
Instead, DEC pretended that all 8" floppy media HAD to be
purchased PRE-FORMATTED from DEC. Well, if you
ever discussed that option with a DEC person, it certainly
did not seem like the individual was pretending.
After I managed to locate a DSD (Data Systems Design)
drive which supported the DEC RX02 floppy drive function,
it was game over for that particular DEC monopoly. The
DSD drive was able to perform an LLF for either single
density or double density in addition to being both single
sided and double sided.
Not that tricky. All you needed was a way to format into RX01 format,
which is plain simple IBM single side, single density format.
RX02 floppies have the same low level formatting. To use them in RX02
mode just requires flipping a bit in the sector header, and the RX02
drive is able to do that. Note that the
RX50 was the same. DEC finally changed
their marketing policy with the RX33 drive which used the
same 3.5" HD floppy media as the PC. It was actually
possible to FORMAT those floppies under RT-11.
No, DEC actually did support users formatting RX50 floppies on their
own, but only on the Rainbow.
Johnny (b) The firmware in the controller on the Rainbow
supported an LLF,
but the firmware in the controller on the RQDX1, RQDX2 or RQDX3
on the PDP-11 did not support an LLF
Quite possible.
(c) The Rainbow used a program which DEC supplied
that could
perform an LLF, but DEC did not supply such a program for
the PDP-11 systems
Also quite possible. And would be what Jay Jager claims. I don't know
myself. I know that RSX refuses to even try formatting an RX50. If it in
fact could, I don't know. But the floppy drive itself obviously could.
(One reason why some places bought Rainbows in fact...)
Take me back to my desk in DECPark thirty years ago
and I could have
pulled out the internal documents on this.
I cant do that so we will have to make do with my dodgy memory.
When floppy disks first appeared end users just wanted to take the
disk out of the box and use it.
They could not see why they should waste time preparing every new one.
They did not need matching to a particular drive as DEC's
manufacturing tolerances made sure any disk would work on any drive.
In fact it was more difficult and expensive to provide pre-formatted
disks.
It was more about customer service and making sure the equipment kept
running.
I heard the following story
One customer went out and got a huge pile of unformatted (and
untested) floppys and a third party format program.
He expected DEC to make it work.
The account manager asked to see his DEC maintainance contract and had
to be restrained from tearing it up.
Through the window of the office was building site and the inevitable
50 gallon oil drum burning rubbish.
He was offered a choice; he could put the disks or the contract in the
burning drum.
Rod Smallwood
DEC supplied pre formatted disks Another problem was that the index hole for
single-sided floppies
was offset about 1/2" from the index hole for double-sided
floppies. That challenge was solved by using a DPDT switch
to flip the sensors that were used on the DSD 880/30 and
that supported using, as double-sided, floppies with the single-
sided index hole. While a number of 8" floppies had been
purchased that had the double-sided index hole, that was less
than 10% of the total and after punching the extra pair of holes
in single-sided floppies just a few times, it was very quickly
apparent that the DPDT switch was a much better one-time
solution. What was initially a surprise was that EITHER the
single-sided OR double-sided index hole could be used with
the same floppy to access the sectors even though the holes
were in different positions. The timing did not seem to matter.
Only the device driver software cared if the bit was set one
way or the other, so flipping the sensors which were activated
was an excellent one-time solution when the user (me!!)
wanted to use a floppy with a single-sided index hole as a
double-sided floppy.
In any case, the code was enhanced, my version of DYX.SYS
supported the RX03 double-density, double-sided floppy drive
under a 22-bit RT-11 monitor. So I set about the job of the
LLFs for double-sided 8" floppy media. As mentioned above,
in addition to a couple of dozen 8" DEC floppies, I had about
a dozen other brands. To make a long story short at this point,
the results were "interesting". Every non-DEC branded 8" floppy
could hold an LLF for double-sided, double-density. On the other
hand, I seem to remember that only about 2/3 of the DEC 8"
floppies managed to complete the LLF. The other 1/3 of the
DEC 8" floppies could hold an LLF on the normal first side,
but not on the second side.
Obviously this story was somewhat different since it was not
necessary to ask DEC maintenance to make the LLF capability
with the DSD 880/30 to work - it already worked. In addition,
there was no DEC maintenance contract in the first place and
there was no 50 gallon oil drum. There was also no refusal
by DEC to enhance the DY.MAC device driver to support
the RX03 floppy drive since DEC was not asked.
Over the decades since, I have always wondered how it was
even possible for ONLY the DEC 8" floppies to be unable to
take an LLF double-sided when every other brand managed
to do so. There was probably one floppy that was so severely
damaged that it would not take an LLF on either side, but that
was a specific exception. Any 8" floppy which could take a
double-sided, double-density LLF held the data successfully
when used in practice.
Probably qualification differences. DEC only cared if one side was good.
So floppies with one bad side were still acceptable for DEC, since they
only used one side anyway.
Floppies sold as double sided needed to pass testing on both sides.
Johnny