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Unformatted text preview: block is larger than the payload. This might happen for a number of reasons. For example, the implementation of an allocator might impose a minimum size on allocated blocks that is greater than some requested payload. Or, as we saw in Figure 10.36(b), the allocator might increase the block size in order to satisfy alignment constraints. Internal fragmentation is straightforward to quantify. It is simply the sum of the differences between the sizes of the allocated blocks and their payloads. Thus, at any point in time, the amount of internal fragmentation depends only on the pattern of previous requests and the allocator implementation. External fragmentation occurs when there is enough aggregate free memory to satisfy an allocate request, but no single free block is large enough to handle the request. For example, if the request in Figure 10.36(e) were for six words rather than two words, then the request could not be satisfied without requesting additional virtual memory from the kernel, even though there are six free words remaining in the heap. The problem arises because these six words are spread over two free b...
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This note was uploaded on 09/02/2010 for the course ELECTRICAL 360 taught by Professor Schultz during the Spring '10 term at BYU.

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