Acronis Disk Director Server 10.0 - User Guide - Manual (Page 92)

Hard Disk And File Systems
92 Copyright © Acronis, Inc., 2000–2005
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.
Table 3. The following table gives the approximate dependence of these
losses versus the cluster size:
Partition Size Cluster Size Waste
<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.