Different operating systems use different file systems. Some operating
systems are able to work with only one file system while other can use
several of them. Let us describe some of widely used file systems in detail.
A.2.1 FAT16
FAT16 file system is widely used by DOS (DR-DOS, MS-DOS, PC-DOS,
PTS-DOS and other), 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. FAT is
the core of the file system. To increase data safety it is possible to have
several instances of FAT (there are usually 2 of them). A cluster is a
minimum data storage unit in FAT16 file system. One cluster contains a fixed
number (some power of 2) of sectors. 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 65525, the largest cluster being 128 sectors. Usually
cluster size is selected as minimum as possible so that the resulting number
of clusters is less than 65526. The larger the partition size, the larger the
cluster has to be. Most of 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.
Like many others, 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 8 characters
long, plus a dot, plus 3 characters of name extension. However, long name
support in Windows 95 and Windows NT bypasses this limitation. OS/2
operating system also supports long names, but does it in another way.
A.2.2 FAT32
FAT32 file system appeared in Windows 95 OSR2 and is also supported by
Windows 98/ME and Windows 2000/XP. FAT32 grew out of FAT16. The main
differences between FAT32 and FAT16 are 28-bit cluster numbers and more
flexible root folder implementation, which is not limited in size. The reason
for FAT32 is the necessity to support large (larger than 8 gigabytes) hard
disks and the inability to build any more complex file system into MS-DOS,
which is still in the core of Windows 95/98/ME.
Maximum FAT32 file system size is 2 terabytes.
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