How to Determine Physical Addresses from Logical Addresses in Segmentation?

[whitehorsey]

1. Given a segmentation table:
Segment Base Length
0 100 200
1 123 75
2 50 150
3 21 14

What are the physical addresses for the following logical addresses (indicate if it's invalid)?
a. (0, 120)
b. (1, 700)
c. (2, 150)

3. a. 120 + 100 = 220
b. Invalid
c. 50 + 150 = 200 Is this valid because it's equal to the size?

So, by adding these numbers we get the physical address? Could you also explain length (like why is it use as an indicator for whether it is invalid or not)?

 

[Valkarie]

Yes, by adding the logical address to the base length you can get the physical address. The length is used as an indicator for validity because it represents the maximum size of the segment. If a logical address is larger than the length, then it is invalid because it cannot be mapped to a physical address.