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
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
of software issues you'll have to deal with. I booted my DEC Rainbow
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.