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Hard Disk And File Systems

A.9.2 FAT16

The FAT16 file system is widely used by DOS (DR-DOS, MS-DOS, PC-DOS, etc.), Windows 95/98/Me, Windows NT/2000/XP operating systems and is supported by most other systems.

Main features of FAT16 are the file allocation table (FAT) and clusters. The FAT is the core of the file system. To increase data safety, it is possible to have several instances of the FAT (there are usually two of them). A cluster is a minimum data storage unit in the FAT16 file system. One cluster contains a fixed number (some power of 2) of sectors. The FAT stores information about what clusters are free, what clusters are bad, and also defines in what clusters files are stored.

Maximum size of a FAT16 file system is 4 Gigabytes, and the maximum number of clusters is 65,525, the largest cluster being 128 sectors. Usually the smallest possible cluster size is selected so that the resulting number of clusters is less than 65,526. The larger the partition size, the larger the cluster has to be. Most operating systems incorrectly perform with 128-sector clusters, thus reducing the maximum FAT16 partition size to 2 Gigabytes.

Usually the larger the cluster size, the more disk space is wasted.

<127 MB

2 KB

2%

128–255 MB

4 KB

4%

256–511 MB

8 KB

10%

512–1023 MB

16 KB

25%

1024–2047 MB

32 KB

40%

2048–4096 MB

64 KB

50%

Like many others, the FAT16 file system has a root folder. Unlike others however, its root folder is stored in a special place and is limited in size (standard formatting produces a 512-item root folder).

Initially, FAT16 had limitations to file names that could only be eight characters long, plus a dot, plus three characters of name extension. However, long name support in Windows 95 and Windows NT bypasses this limitation.

Table 3. The following table gives the approximate dependence of these losses versus the cluster size:

Partition Size

Cluster Size

Waste

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