Disadvantages of Address translation:
Disadvantages are following:
- A program that is too large to be held in a part needs some special design, that called
overlay, which brings heavy weight on programmers. Having overlay, a process consists of various portions with each being mapped to the similar location of the partition, and at any time, only 1 portion may reside in the partition. When another part is referenced, the present part will be switched out.
- A program can be much smaller than a part, thus space left in the partition is going wasted, which is referred to as internal fragmentation. As an improvement shown in above figure (b), unequal-size partitions can be configured in primary memory so that small programs will occupy small partitions and large programs are also likely to be able to fit into large partitions. Although this can solve the above problems with fixed 5 equal-sizes partitioning to some degree, the basic weakness still exists: The number of partitions are the maximum of the number of processes that could reside in primary memory at the same time. When mostly processes are small, the system would be able to accommodate more of them but fails to do so due to the restriction. More flexibility is required.