Dec RQDX: What kind of chips on it?

Ethan Dicks ethan.dicks at
Tue Jan 5 11:22:20 CST 2021

On Tue, Jan 5, 2021 at 9:20 AM Paul Koning via cctalk
<cctalk at> wrote:
> It's surprising that the RQDX3 wasn't made format-compatible with the older controllers.

I think it's more of a case that DEC completely rolled their own
controller for the RQDX1/2 and gave it and went with a standard (SMC)
controller for the KA410 (uVAX 2000) and the RQDX3.

I have no specific knowledge of their process, but it seems likely
that they had two engineering goals around the same time: make a
lunchbox VAX and create the follow-on hard disk controller for Qbus
MicroVAXen that could support larger disks than the RQDX2, and that
one effort likely borrowed from the other (why reinvent two wheels at

The fact that you had to toss out your old RQDX2 to put a larger disk
in the machine was already a given so there was no need to support a
backwards-compatible on-disk format.

I'm just happy that the KA410 and RQDX3 have compatible formats.
That's been handy over the years.  I do have one uVAX I with an RQDX1
(that I should probably see about imaging, but as mentioned, it's easy
enough to use vtserver - just pull the KA610 processor and install a
KDF11 or KDJ11 board (and a grant card) at the top.


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