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lecture20 - File System Implementation In order to create...

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File System Implementation In order to create the illusion of files from the block oriented disk drives, the OS must keep track of the location of the sectors containing the data of the file. This is accomplished by maintaining a set of data structures both in memory and on disk that keep track of where data is allocated to each file, and the name to file mapping encoded in the directoiry structure. The simplest alloaction of files is a contiguous allocation of sectors to each file. Adirectory entry would contain the name of the file, its size in bytes and the first and last sector of the file. This results in a fast read of a givenfile and a compact representation, but also of sizable external fragmentation which can require compaction to correct. The analog in memory management is the base/limit register system of memory allocation. As with memory management, we turn to more complexdata structures and non contiguous alloca- tion to solvethe problems. We can use a bitmap to record the allocated and unallocated sectors on the disk, and keep a list of sectors assigned to each file in its directory entry .This isn’
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lecture20 - File System Implementation In order to create...

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