Dec RQDX: What kind of chips on it?

Antonio Carlini a.carlini at
Tue Jan 5 06:36:52 CST 2021

On 05/01/2021 11:47, Joshua Rice via cctalk wrote:
> I’m not sure where i read it, but i’m pretty sure the main “brains” of the RQDX2 is a T-11 (PDP-11 FALCON) chip, and that does the negotiations between disk and system. I don’t know if it’s the same for the RQDX3, but i’d suspect not, as the incompatabilities between the 2 and 3 are probably due to a controller redesign. Though i really am no expert when it comes to disk controllers, and barely qualify as an amatuer with QBUS PDP-11’s in general!

The RQDX3 definitely uses a T-11 (the controller User Guide says so). I 
don't know what the RQDX2 uses, although Wikipedia says that uses a T-11 
too. They can use (at least) some of the same RDxx disks but the format 
is incompatible between the two AFAICR. So you could move an RD53 (say) 
from an RQDX2 to an RQDX3 (or vice versa) but you'd have to reformat it 
to use it: you could not read data written by an RQDX2 on an RQDX3 
(again, AFAICR).

I think that the (even older) RQDX1 was very similar to the RQDX2 but 
had a design fault that meant it had to be the last module on the bus 
(it failed to pass on the grant signal, I think).


Antonio Carlini
antonio at

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