Gavin writes:

>Stan writes:
>> HP-UX *barely* uses any of the addressing capability of PA-RISC.
>
>HP-UX pre-11.0 uses only implicit 32-bit pointers, and provides no APIs
>capable of accepting (or giving) a 64-bit segmented address (long pointer).
>
>> MPE/iX uses all of it!
>
>The 64-bit version of HP-UX 11.0 uses 100% of the enhanced 64-bit addressing
>capabilities of PA-RISC 2.0.  Memory appears to a process as a flat 64-bit
>address space.  Each process has its own 4 TeraByte stack, 4 TeraBytes of
>"text" (program code), and access to 8 TeraBytes of shared data objects
>(like mapped files)...

I will point out that this scheme isn't quite as flexible as Gavin
suggests. There is only a 32-bit space register, meaning that the OS can
manage, at most, 2^32 - 1 processes.

>The current 16TB addressing limit of HP-UX 11.0 is a software convention,
>rather than a hardware limit as in PA-RISC 1.x.  It can be expanded as
>needed (as soon as someone writes a program bigger than 4TB :-)

I distinctly remember being in a technical roundtable session at the
Interex (then HPIUG) conference in Edinburgh in 1983. They were
discussing the 32-bit address space that Vision was going to have, and
announced that 4GB would be enough for the foreseeable future. I predict
16TB is going to seem as laughably small in 2015 as it seems laughably
large now.

>If MPE ever becomes a real 64-bit OS, then it will be able to take advantage
>or the HP-UX way of doing things (Note that becoming 64-bit and running on
>IA-64 are two *unrelated* issues).

Not completely, since the MPE lab is a lot more reluctant to fork OS
development than the Unix folks. HP 3000s are expected to last five years
or more, meaning that forking the OS to allow a true 64-bit MPE would
leave out all the PA-RISC 1.x systems manufactured in the last five
years. The timeframe for the second-generation IA-64 chip is just about
the earliest that HP could reasonably cut off all the 1.x people from new
OS development.

-- Bruce


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