VAX Q-bus identical to PDP-11 Q-bus?

Jerry Weiss jsw at
Thu Dec 7 18:02:07 CST 2017

> On Dec 7, 2017, at 1:22 PM, allison via cctalk <cctalk at> wrote:
> …..
> As such PDP11 and VAX support is there unless the OS in non-DEC in
> origin and even then if the
> time frame made it a marketing requirement the third party OS vendor had it.
> An example is a RD54 on a Qbus PDP-11 running RT11.  You need the LD
> driver to partition the
> disk as RT supports only 32mb or smaller devices and the RD54 is 150.  
> It was supported but
> not ever sold that way.
> Things like block replacement are options of the OS and the device IO is
> then just a
> interface.  The protocol for to talk to the device is a lower level
> layer in most cases.

I think you are actually referring to the logical partitioning in the DU handler under
RT-11.  The DU (MSCP) handler managed this and had the ability to allow
the disk to handle bad block replacement (RA type device) or do it in the controller (RD).

The KZQSA is not listed as supported in V5.6.   i have not seen documentation
on how it configured SCSI drive support.  I would be interested to know if anyone tried
to use it under RT-11.


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