Dec RQDX: What kind of chips on it?

Warner Losh imp at
Tue Jan 5 10:00:35 CST 2021

On Tue, Jan 5, 2021, 7:20 AM Paul Koning via cctalk <cctalk at>

> > On Jan 5, 2021, at 6:56 AM, Joshua Rice via cctalk <
> cctalk at> wrote:
> >
> > These links may help:
> >
> > <
> > ...
> > There’s definitely incompatabilities between the RQDX2 and RQDX3. They
> shouldn’t be assumed to be designed or act similarly, despite their names.
> The only similarity is that the RQDX3 can read the same floppy disks as the
> RQDX2 formats.
> It's surprising that the RQDX3 wasn't made format-compatible with the
> older controllers.
> As for floppies, the RX50 format is the same for all PDP-11/VAX systems.
> Unlike hard drives, Pro floppies and RQDX3 floppies are identical.  The
> geometry is handled in the host for the Pro and in the controller for the
> RQDX case, but it's the same geometry.  And by the way, a PC floppy drive
> can handle RX50 floppies without any trouble, if you set it to the correct
> geometry -- in particular, you have to tell it there are 10 sectors per
> track rather than the PC default of 9 sectors.

Reading this is true. There are several drivers for this for DOS, linux and
FreeBSD (though the latter may be out of tree). Writing on PC and reading
on a Rainbow is possible, but it is unreliable because the 1.2M drives
aren't that good at writing lower the lower density data rates.

Fun fact: the 720k 3.5" floppies can handle 10 sectors per track just fine.
You can boot a Rainbow off one of these even, but I didn't keep that setup
for reasons I don't recall..



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