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| • |
Paging
is invisible to programmer, but
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segmentation
is not
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• |
Even
paging with two-level page tables is invisible
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| • |
Segment:
an open-ended piece of VM
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• |
Multics
(H6000): 218 segments of 64K words each
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• |
Pentium:
16K segments of 230 bytes each
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– |
8K global
segments, plus 8K local segments per process
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– |
Each
segment may be paged or not
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– |
Each
segment assigned to one of four protection levels
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| • |
Program
consciously loads segment descriptors
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when
accessing a new segment
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• |
Only
OS/2 used full power of Pentium segments
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• |
Linux
simply concatenates 3 segments to provide process VM
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