🚀 go-pugleaf

In article <MOSS.92Jul26183952@ibis.cs.umass.edu>, moss@cs.umass.edu (Eliot Moss) writes:
|>
|>3) Kernel space is the third quarter of the address space, as previously
|>noted, and is generally shared among all processes (but pages have different
|>protections in user, exec, supervisor, and kernel modes, so this is safe,
|>etc.)
|>

This is S0 space.

|>4) The fourth quarter of the address space is generally used for I/O devices
|>and could be called "I/O space", though I am not sure if that is an "official"
|>designation.
|>

Here you're confusing the high-address physical address space and virtual
address space.  The high-address physical addresses are indeed I/O space, but
the high-address virtual addresses are S1 space, which has been "reserved for
future expansion" in most VAX implementations, and was finally defined as an
extension of S0 space to double the system vitrual address space in the newest
VAX implementations.

As a side note, not all operating systems use the virtual address regions the
same way.  VAXELN uses an interesting partition of the three available
address spaces.  S0 is shared by all jobs in the system, P1 is shared by all
processes in a job (but not between jobs), and P0 is private to each process.

Paul