On Mon, Feb 27, 2023 at 11:10 AM Christian Corti via cctalk < [email protected]> wrote:
> 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 > HD). > Correct. You don't need a 1.2M drive. That's true. However, getting the 96tpi QD 300prm 250kHz drives are a lot harder these days than finding an old 1.2M drive. I recently looked for the TEAC 55FR drives that I used back in the day, and could not find them at all. Found plenty of other TEAC 55xx drives that were all either '360k' or '1.2M' drives. So it was more of a practical bit of advice, than an absolute requirement... 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. IDrives used a transistor to switch the signals properly for these drives. I opted to use drives that didn't need this signal. For 3.5" drives, there weren't any hacks 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. > > 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 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 there, 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 250kHz 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, since those 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 jumpers. Wrote a 'driver' for it called IMPDRIVE back in the day. Some 5.25" drives would 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... Warner
