4 floppy disk drives on a PC?

[Paul Koning]

Tony,

Nice discussion of the various floppy formats.

One point you didn't mention is that the standard PC format has 9
sectors per track, while the DEC RX50 has 10 sectors per track.  So in
fact the RX50 does not have the same capacity as the double sided
48tpi PC floppies -- it has 10% more because of the higher sector
count. 

PC floppies can read and write RX50 format, given a 96tpi capable
drive.  You can do it under DOS by using direct BIOS calls (int 13);
under Linux, by setting the drive parameters to match the RX50
format.  

In addition, the RX50 logical block number to c/h/s mapping is odd.
There is a 2:1 interleave, which is reasonable enough.  Harder to
explain is that logical block 0 is in cylinder 1, and cylinder 0
contains the last 10 blocks.

I can supply details and sample code if anyone is interested (or you
can find my utility "rstsflx" which has all this -- John Wilson's file
server has a copy, as does Johnny Billquist if I remember right.

       paul