Re: teraspace, user spaces, etc.

In the single level store:  The individual pages within a segment are
contiguous addresses.  This includes user spaces.

It is the segment identifiers themselves are discontiguous.  The system
ensures that one cannot address outside of the boundaries of one's current
segment.  Thus, if one loads an MI space pointer, it cannot be made to
address some unrelated segment.  It can reference any valid byte in its own
segment, one way or another.

Think of the segement identifier of the space pointer as an unmodifiable
token and the offset as a more-or-less standard virtual address.  The thing
that makes single level store what it is is:  1) the unmodifiable token is
more-or-less visible to the problem state program in the MI pointer,  2) an
MI pointer can be passed between jobs and used identically in both.

In general and in practice, one cannot allocate multiple segments (e.g.
multiple user spaces) and expect the segment identifiers that result to be
numerically adjacent.  Even if they were (and, they won't be), the system
will behave in a manner to make any adjacency of segment number irrelevant.
The "token" aspect of the segment identifier is virulently enforced, as you
would expect.


Larry W. Loen  -   Senior Java and iSeries Performance Analyst
                          Dept HP4, Rochester MN


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