Multi-platform distribution format (Was: Backups [was

Jerome H. Fine jhfinedp3k at
Mon Sep 21 19:31:24 CDT 2015

 >tony duell wrote:

>>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
>It is. Remember the RX50 is just a drive, it does not include any of
>the controller electronics.
>>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
>It's more the reverse!. The Rainbow just has a standard controller chip on the 
>processor bus (I forget which processor, I can look at the schematics if you
>want). The controller chip can do what is needed for a LLF, and there is
>nothing in the way to prevent software from sending the commands to do
Well that is a reverse explanation!  Completely opposite of
what I thought might be the actual situation.

>On the PDP11 there is a lot more stuff between the processor and the disk
>controller chip. Even the Pro 300 series has a microcontroller (8051?) on
>the floppy controller board. Therefore the processor you can program
>(PDP11) can't do arbitrary things to the disk controller chip, it is very likely
>that sending the right commands to do an LLF is one of the things you
>can't do.
HOWEVER, while the PDP-11 is still unable to perform an
LLF on an RX50 when an RQDX3 is present, it is possible
to perform an LLF on a floppy in an RX33.  Does that still
seem compatible with your explanation?

I would not attempt a trick question with you since I don't
know enough to set one up.  Again, I am just trying to
understand what DEC did and how DEC managed to
still avoid being able to perform an LLF on an RX50
using an RQDX3, yet supported an LLF right from
RT-11 on the RX33 using an RQDX3?

The one time I watched it being done, I nearly fell off
my chair in astonishment.  After all those decades using
the PDP-11, I was finally allowed to FORMAT a floppy
and it actually worked.  Of course, the floppy in question
was identical to a HD 5 1/4" PC floppy which any PC
at that time would also be able to FORMAT.  And in
any case, the floppies were usually sold with a FORMAT.
So all that would normally be needed would be the
INITIALIZE command.  But it would be nice to be
able to understand how the RQDX3 can FORMAT
an RX33, but not an RX50.  I also have an RX23
drive on a CQD 220/TM which I have never tried.
But since that is a non-DEC host adapter, I don't
think it counts,

Jerome Fine

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