Yay, now I need some Osborne boot media!

tony duell ard at p850ug1.demon.co.uk
Mon Nov 24 12:54:58 CST 2014

> The flamewar about RX02 is based on defining what is meant by the phrase
> "MFM floppy"!  Nobody is "wrong", they just aren't recognizing each
> other's definitions.  The RX02 is NOT an "FM floppy"; the RX02 is NOT an
> "MFM floppy".  It is a hybrid.  It took an FM low level format, and
> rewrote the data area of each sector with MFM, resulting in a disk that is
> about 1/3 FM, and 2/3 MFM.  In terms of the floppy ITSELF, disks rated for
> FM or rated for MFM should both work, but there might be better
> reliability using the MFM rated disks.  AND NOT the 600 Oerstedt "1.2M"
> disks!  THOSE might seem to work, but will be blank again before you need
> to reread the disk!   BTDT.

If you can make a real DEC RX02 unit do anything useful with a PC type 
'1.2M' disk then I feel like saying I will eat one. The RX02 drive. It's a 
dual 8" unit...

As I mentioned, there were 3rd party Qbus boards that did RX02 format
using normal 8" drives (SA800 type), Many also supported double-sided
operation (The hooks for that were in the drivers in most DEC OS's, the
DEC RX02 had almost all the electronics for it, other than the 'down' heads).

I suspect that with the right cabling these boards could be used with PC
type HD drives. In which case you _would_ want 600 Oestedt disks,

> And, NO, the 765 can't be tricked into reading RX02.
> Or can it?  PROVE ME WRONG - write the code to do it!

I've never heard of it being done. Those 3rd party RX02 compatible
controller boards didn't use a standard FDC IC. They used a 
custom controller (often a pair of 2901s, a 2910 and microcode PROMs
plus a lot of extra logic).


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