August 1997
SW204: SOFTWARE AND FILES DESIGN

QUESTION 4

Total Marks: 20 Marks

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4. (a) What are partitions? [2]
Partitions are separate areas of main memory [1]
that can be used to store different (or separate) programs. [1]
Similar answers should also be awarded marks.
(b) What is the purpose of partitioning? [2]
Partitioning enables multiprogramming [1]
and multitasking operations to be carried out. [1]
Similar answers should also be awarded marks.
(c) Paging and segmentation are widely used methods in many large general purpose time-sharing systems for memory management.
(i) What is segmentation? [1]
Segmentation involves breaking up a program into variable sized chunks. [1]
One mark for any answer with a similar content, although the fact that segments are of variable size (for segmentation of programs) must be mentioned.
(ii) What is paging? [1]
Paging involves breaking up a program into equal sized chunks. [1]
One mark for any answer with a similar content, although the fact that pages are of fixed size (for segmentation of programs) must be mentioned.
(iii) How does fragmentation for segmentation differ from that in paging? [2]
It is the same, [1]
except for the fact that segments are of variable length. [1]
(iv) What two advantages does segmentation have over paging? [4]
One mark should be awarded for each valid point and one mark should be awarded for each acceptable elaboration. Examples of valid points include the following:
It provides protection over critical sections.
It enables sharing of code and data with other users.
(d) One of the major problems of paging and segmentation is the presence of fragments in memory which is wasted.
(i) Distinguish between external and internal fragmentation. [2]
Internal fragmentation is wasted space within a partition, [1]
whereas external fragmentation is wasted space due to empty partitions being too small for current processes. [1]
Similar answers should also be awarded marks.
(ii) List two ways by which fragmentation can be managed. [2]
One mark should be awarded for each valid point. Examples include compaction and coalescing.
(iii) Briefly describe each of the methods mentioned in part (d) (ii). [4]
Compaction involves moving all of the used partitions to one side and keeping the unused ones together. [2]
Coalsecing involves merging two adjacent free partitions. [2]
Similar answers should also be awarded marks.