On computers that dual-boot these two operating systems, files that created when running one of the operating systems can be accessed when running the other. Data Recovery. Data Utility. Data Security. Data Backup. LSoft Technologies Inc. Toggle navigation. File allocation table is a table for describing the allocation status of the clusters the basic units of logical storage on a hard disk in the file system and the link relationship between the file contents.
You can simply say it is a table in which the file is located. It is a vital part of the FAT file system, and it is also very important for the use of the hard disk. If the file allocation table is lost, the data on the hard disk cannot be located and cannot be used.
When a new file is written to the hard disk, the file is stored in one or more clusters that are not necessarily adjacent to each other; they may be fairly widely distributed across the disk. The operating system creates a FAT entry for the new file, recording the location of each cluster and its order. When you read a file, the operating system reassembles the file from these clusters and places it as the entire file where you want to read it.
Next-available: Finds next available entry from the last allocated entry; at end of directory chain, start again at beginning e. FAT table entries are packed so that two cluster entries occupy three bytes with the following general format:.
The starting cluster in the directory is also a pointer into the FATs linking to the next cluster in the file. The physical size of this file is five clusters bytes , and occupies clusters 73, 74, 75, 76, and 77 on the medium.
It is merely a coincidence that the clusters are contiguous. The table has one entry for each disk block and is indexed by block number. File allocation table needs to be cached in order to reduce the number of head seeks. Now the head doesn't need to traverse all the disk blocks in order to access one successive block. It simply accesses the file allocation table, read the desired block entry from there and access that block. This is the way by which the random access is accomplished by using FAT.
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