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memory may remain unused in such systems due to internal fragmentation.
2. When the system uses variable number of variable-sized memory partitions, it
may happen that there is a free block of size 200K and a new process arrives
whose memory requirement is 199.5K. If we allocate exactly the requested size of
memory, we will be left with a free block of size 0.5K. Considering the overhead
involved in keeping track of this 0.5K free block, the general approach is to
allocate such small memory areas as part of the process's memory request. Thus,
the allocated memory may be slightly larger than the requested memory, and the
additional memory that gets allocated to a process in this way is an internally
fragmented memory space.
Paging We saw in the discussion above that memory compaction is a mechanism used to
solve the problem of external fragmentation. We also saw that memory
compaction is an expensive operation requiring lot of CPU time because it
involves copying memory contents from one memory location to another to make
scattered free space contiguous. Paging is another mechanism used to solve the
problem of external fragmentation. It is considered to be better than the memory
compaction mechanism because it solves the problem of external fragmentation
without the need to make scattered free space contiguous. Rather it allows a
process's memory to be noncontiguous, thus allowing a process to be allocated
physical memory wherever free memory blocks are available. Because of its
advantage over memory compaction mechanism, paging mechanism (in its various
forms) is used in many modern operating systems. How this mechanism works is
In this mechanism, the physical memory of a computer system is partitioned into
fixed-sized blocks called page frames. The total memory requirement of a process
(including its instructions and data) is also partitioned into blocks of the same size
called pages. Page sizes are typically of the order of 1 Kilobytes to 8 Kilobyte...
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This document was uploaded on 04/07/2014.
- Spring '14