Segmentation

Question 1

what is segmentation?

Answer 1

• a memory management scheme that supports the user view of memory
• logical addresses space is a collection of segments containing data associated with a particular logical entity
• segments are addressed by a fixed id number
• address consists of
• user is aware of the segmentation, unlike paging

Question 2

what is a segment table>?

Answer 2

• address mapping via a segment table (per process)
• an entry for each segment addressable by the process, with base and limit values
• offsets are checked against limits, trapped if illegal, added to base to get physical address

Question 3

how does fragmentation affect segmentation?

Answer 3

external fragmentation may occur because phsical memory is contiguously allocated
but we can fix this by paging the segments
woa

Question 4

describe segmentation protection?

Answer 4

we have an advantage in protection, as its likely that all data in a segment will be used in the same way

so we can associate a protection level with a partiuclar segment
- read/write/execute permissions

Question 5

how does paging relate to segmentation?

Answer 5

each segment is a paged address space with its own page table
gives us the benefit of segmentation without external fragmentation

segment number indexes the segment table
base address and offset combined into a 1D address
page table for segment used as normal