Importance

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Abstract

A file system includes a file allocation table (FAT) and a file allocation table extension. Each FAT element of the file allocation table corresponds to a unique cluster on disk and represents the status of that cluster. These FAT elements are indexed by a cluster number that corresponds to that cluster on disk. Each element of the file allocation table extension does not correspond to any region on disk. Writing a file divided into clusters to disk first involves determining whether the cluster may be represented by a hole. If not, the cluster is written to disk at a particular cluster number and a status indicator is stored in the file allocation table at a FAT element indexed by that cluster number indicating that the cluster is allocated. If the cluster may be represented by a hole, a status indicator is stored in the file allocation table extension at an element indicating that the cluster is not stored on the disk of the computer. The status indicators in the FAT and FAT extension form a linked list representing the clusters of a file. The holes of the FAT extension may also be used to store compressed files. A plurality of file allocation table extensions may be used. One file allocation table extension may indicate holes in stored data that result from expanded files having clusters full of zeros. Additional file allocation table extensions may be used to represent holes in stored data that result from the use of various compression algorithms on the data. Each FAT extension may represent holes resulting from the use of a different compression algorithm.

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