24 Nov
2014
24 Nov
'14
10:54 a.m.
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).
-tony