> 
>   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 of process-space addresses is different on an
>   rtVAX than described in Chapter 4. *
> 
This would require quite much memory in the machine to be useable.
If the user PTEs must be in physical memory, the memory must be contiguous,
and therefore it must be allocated at boot. This means that page tables
for one process of size 32MB would require 256K physical memory, and
the possibility to have 50 processes would need 12MB pre-allocated memory.

-- Ragge