27 Feb
2023
27 Feb
'23
6:10 p.m.
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. :-)
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
HD).
Using 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 5ΒΌ" 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.
Christian