3 what is the difference between internal and external fragmentation

However, this free space is unusable as the memory allocator only assigns full partitions to programs but no t parts of it. This wastage of free space is called internal fragmentation. In the above example, it is equal sized fixed partitions but this can even happen in a situation where partitions of various fixed sizes are available.

Usually the memory or hardest space is divided into blocks that are usually the size of powers of 2 such as 2, 4, 8, 16 bytes. So a program or a file of 3 bytes will be assigned to a 4 byte block but one byte of that block will become unusable causing internal fragmentation. Consider the figure above where memory allocation is done dynamically. In dynamic memory allocation, the allocator allocates only the exact needed size for that program.

First memory is completely free. Then the Programs A, B, C, D and E of different sizes are loaded one after the other and they are placed in memory contiguously in that order. Then later, Program A and Program C closes and they are unloaded from memory. Now there are three free space areas in the memory, but they are not adjacent. Now a large program called Program F is going to be loaded but neither of the free space block is not enough for Program F. The addition of all the free spaces is definitely enough for Program F, but due to the lack of adjacency that space is unusable for Program F.

This is called External Fragmentation. Memory block assigned to process is bigger. Some portion of memory is left unused, as it cannot be used by another process. The internal fragmentation can be reduced by effectively assigning the smallest partition but large enough for the process. Total memory space is enough to satisfy a request or to reside a process in it, but it is not contiguous, so it cannot be used.

External fragmentation can be reduced by compaction or shuffle memory contents to place all free memory together in one large block. Advanced Data Structure. Operating System. Computer Network. Computer Architecture. Android Development. Game Development. GO Language. Spring Framework. Go to Tutorials Library. Interactive Courses, where you Learn by doing. Available for FREE! Tutorials Library. MCQ Tests.

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