On Tue, 12 Nov 2002, Roger Ivie wrote:

> I've changed the subject because, as someone else pointed out, there are
> several rtVAXes.
>
> The original rtVAX used a special implementation of the MicroVAX II. As I
> understand it (and I've not seen any technical specs on the processor, so
> this could just be lunatic rantings), the change made for the original
> rtVAX was to not allow user-mode page tables to be paged. I don't know the
> details; sorry.

The 2nd Ed. VARM discusses the rtVAX, but doesn't mention specific
models, but I'd gather this would be characteristic of all of them:

   [p. 422]

   11.2.3 rtVAX Memory Management

   The rtVAX is a variant of the VAX Architecture.  An rtVAX processor
   implements the per-process page tables in physical memory.  All other
   VAX processors implement the per-process page tables in virtual
   memory. Therefore, translation of process-space addresses is
   different on an rtVAX than as described in Chapter 4.

   [blah blah, details, blah...]

More recently, I've also heard about system known as the ftVAX which is
a "fault tolerant" version of the VAX.  I don't know anything about it
apart from it being designed for critical applications.  The one
significant reference I can find to it in Google is in a PDF document
for some evil Windows 2000 system:

   http://www.marathontechnologies.com/news/ent9.pdf

   [...]
   I recall working on the ftVAX (Fault Tolerant VAX) from Digital
   Equipment Corp. many years ago. I was impressed with the architecture
   and design. I remember the demo of the ftVAX that showed how the four
   boxes consisting of multiple CPUs and mirrored disks could be
   dismembered piece by piece and, as long as at least one of each
   critical piece was still functioning and properly connected, the
   system kept on going without a hiccup.

-brian.