>From: allisonp@world.std.com (Allison J Parent)

>< RX50s are 80 tracks, single sided, double density. They will work only
>< reliably with 360K floppies, preferably ones without a hub ring.
>
>No 360k floppies do not!  RX50 is 96tpi and 360k are 48tpi.

You're right that 360 KB floppies are not officially rated for 96 TPI,
but in practice they seem to work fine.  For years the disk companies have
been telling us that we can't use disks beyond the purpose they're sold for,
but we all know that it's cheaper for them to have one manufacturing line
for each distinct type of disk and leave it at that, so they're just peeved
that they got caught artificially segmenting the market.  It would be pretty
difficult to make disks that work perfectly at 48 TPI but not at 96 TPI
using the same data rate, they'd need to have carefully aligned concentric
circles of oxide or something.  Anyway 1.2 MB disks will certainly not work
reliably as RX50s so unless you know where to find DD disks that officially
support 96 TPI, 360 KB disks are your only choice.

>Putr with a 1.2mb tricked to single sided 250kbS mode is equivilent to
>RX50.

No trickery involved, 250/300 kHz mode is fully supported on 1.2 MB drives
since that's how they access 360 KB disks.  Which doesn't work too well
for PC 360 KB disks because the tracks are the wrong width (even if they're
spaced correctly), but it's just right for RX50s.  Whether the drive runs
at 250 kHz/300 RPM or 300 kHz/360 RPM is the FDC+FDD's business (most newer
systems use single-speed drives and multi-speed FDCs rather than the other
way around since it's cheaper), the software can't tell the difference and
the media are the same either way.

John Wilson
D Bit