Richard Gambrell ([log in to unmask]) wrote:
: Someone knows, I'm sure:
 
: What is so fundamental about a 2 or 4 GB limit on files size (for both
: MPE and HPUX)?
 
For MPE 4GB is the limit because the offset of the space and offset
address in PA-RISC is 32 bits.  MPE files are mapped into virtual memory
and are addressed by space and offset.
 
HPUX uses the 32 bits as a signed integer, thus 2 GB.  For a long
time in HPUX, a file system could only be 4 GB.  In MPE, I believe
the limit for a volume set is in the tera byte range.  This I believe
is a Label Table Limit.
 
The obvious question is:  with space and offset, we have 64 bits, why
can't we address more than 4 GB.  Because the instruction set does not
allow an offset addition to carry over to the space.  The Virtual
Manager would have to allocate contiguous space IDs.  Many MPE tables
would grow and the Label Table would really have to change.
 
- Rick
 
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Rick Ehrhart
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