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A Note on Storage Fragmentation and Program Segmentation
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Professor Brian Randell
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The main purpose of this paper is to present some of the results of a series of simulation experiments investigating the phenomenon of storage fragmentation. The different types of storage fragmentation are distinguished. The first is external fragmentation, namely the loss in storage utilization caused by the inability to make use of all of available storage, after it has been fragmented into a large number of separate blocks. The second type is internal fragmentation, the loss of utilization caused by rounding up a request for storage, rather than allocating only the exact number of words required. The most striking result obtained is the apparently general rule that rounding up requests for storage, so as to reduce the number of different sizes of blocks co-existing in storage, causes more loss of storage by increased internal fragmentation, than is saved by decreased external fragmentation. The final part of the paper describes a method of segment allocation, and an accompanying technique for segment addressing, which take advantage of the above result. Evidence is presented of the possible advantages of the method over conventional paging techniques.
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