As already said here most of the better DSDD diskettes could handle 48 or 96 TPI.

The biggest problem I remember from that era (on 6809 Systems in the early '80s and early PC's) is intermixing 48 and 96 tpi drives and reading/writing both drives.

Since the tracks are half as wide on the 96 TPI drive, if you format a disk on a 48 TPI drive and then write to it on a 96 PTI drive and then try to read it back on a 48 TPI drive, the reads may fail because the 96 TPI drive only wrote half of the track as seen by the 48 TPI drive.  When reading data on a 48PTI drive, the drive would see half the new data and half the old data.

Also the 96 TPI drive needed to be double stepped to read a 48 TPI formatted diskette.

On 2/27/2023 12:10 PM, Christian Corti via cctalk 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. :-)

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 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.

Christian

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