On Mon, Feb 27, 2023 at 11:10 AM Christian Corti via cctalk <
On Mon, 27 Feb 2023, Warner Losh wrote:
You should be using QD floppies, but those are
rare. DD floppies from
later than 1985 though work just fine (discovered empirically while a
Are they? I guess that I have at least as many QD floppies as DD, if not
even more. :-)
I'd guess at least as many HD floppies, likely way more. QD was a pretty odd
duck, and any
However, in a
PC, to write these diskettes, you need a 1.2M drive. While
there is a couple of TEAC drives (55FR I think) that do 80-tracks at the
DD/QD RPM and data rates, things get fussy putting them into PCs. And
last time I looked they were 5x the price of ye-olde-generic 1.2M floppy
drive. As long as it's formatted at the right density/rpm rates, it's
fine. And RX50.SYS, if memory serves, does all that right.
When giving an advise, it should be as correct as possible ;-))
So no, you don't need a "1.2M drive" (i.e. high density). You just need a
96 tpi drive. And the drive is totally (well, almost) ignorant of the data
rate. It is just spinning the media at a specific velocity (300 or 360
rpm). When using a 300 rpm drive, you need a 250 kHz data rate for DD (QD
is the same, it's just a marketing name for 96 tpi DD). With 360 rpm you
need a 300 kHz data rate. It only gets a little bit complicated if you
jumper a high-density drive for dual-speed mode (300 rpm if DD, 360 rpm if
Correct. You don't need a 1.2M drive. That's true. However, getting the
300prm 250kHz drives are a lot harder these days than finding an old 1.2M
I recently looked for the TEAC 55FR drives that I used back in the day, and
not find them at all. Found plenty of other TEAC 55xx drives that were all
'360k' or '1.2M' drives. So it was more of a practical bit of advice,
While several of the newer drives do allow dual speed operations, the floppy
cables for the RX-50 drive don't have the necessary signals to switch them.
used a transistor to switch the signals properly for these drives. I opted
drives that didn't need this signal. For 3.5" drives, there weren't any
needed because that signal was ignored by most of the drives.
I rarely used them on a PC back in the day, so I'll defer to others on that.
3.5" drives in double density mode will work, but there's a cascade
of software issues you'll have to deal with. I booted my DEC Rainbow with
It would be the same for a normal 5¼" double sided drive. IIRC the trick
is to combine the RX50 specific drive selects to one drive select and one
head select. The software should not know anything about this. Drive 0
would be side 0, and drive 1 side 1.
The trick is just to use two double sided drives, the side select stuff is
and you just need to jumper the drives to be ID0 and ID1 to get your A & B
drives. You have to use for this, though, drives that can do 300rpm at
because that's what (at least the Rainbow) RX-50 controller puts out. I ran
this way for many years, though the software changes to MS-DOS were a bit
flakey for me, and I never found ones for CP/M.
I only got the 3.5" floppy drives that were the lower density to work,
were also 300rpm/250kHz. I never got the high density ones to work since at
least the ones I looked at didn't have the density signal, nor density
Wrote a 'driver' for it called IMPDRIVE back in the day. Some 5.25" drives
work with it (like the TEAC 55FRs), but many would not. And my old FRs are
toast and I've not been able to find good replacements to try this again...