> On Feb 22, 2022, at 7:33 PM, Fred Cisin via cctalk <cctalk@classiccmp.org>
> wrote:
>
> From the FDC point of view, which doesn't have optical view of the drive and
> media, the 80 track DD 5.25" looks similar to a "720K 3.5" drive.
> (80 tracks, 9 sectors per track, 300 RPM, 250K data transgfer rate)
>
> On SOME PCs, setting the CMOS floppy setting to "720K" may take care of it.
Originally I wrote my RX50 floppies on a Windows PC. The drive was a plain old
5.25 inch PC drive, normally used for 9 sector per track PC floppies. It turns
out some BIOS operations will reset it to 10 sectors, which is RX50 format, and
then BIOS int13 operations can read and write it. I coded up support for that
in RSTSFLX, which can be found on my Subversion server (in branches/V2.6). The
original version was built with Borland C++, but I switched to DJGPP which made
all that much easier. No CMOS or other magic needed, just an application that
knows how to speak int13. And of course an old enough Windows, or plain DOS,
which allows you to do those operations.
Subsequently I moved all this to Linux. There is (was?) a tool -- fdparm? --
that you could use to tweak the floppy layout settings. A simple entry in its
config file would give the RX50 layout. Then it's just a matter of handling
the sector interleaving, track skew, and odd track numbering. With just a few
more lines of code, the application can handle the parameter setting so no
prior setup is needed, which is what I ended up doing in RSTSFLX (in C). The
latest version does this as well, but in Python.
So as far as I can see, all this stuff is perfectly easy if you just use a
plain ordinary floppy drive.
paul
