Dec RQDX: What kind of chips on it?

Paul Koning paulkoning at
Tue Jan 5 08:20:07 CST 2021

> 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.


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