Microsoft Windows Files Systems

A computer file system described most simply is a process for organizing and storing computer data files. The file system, at the very least, must ensure that files are stored safely and are readily available for retrieval. At a minimum a file system must allow the operating system to write new files of data to the storage disk while at the same time protecting files previously stored, ensuring they do not get over written. And finally, a file system must make the stored files easy to find and quick to retrieve.

A discussion about Microsoft's file system requires a review of the history related to how these file system were introduced and the needs they were trying meet. The Microsoft operating systems have come to dominate the business and personal computer market. As they were beginning with their very first operating system it was necessary for them to develop a file system. And over the years Microsoft has changed their file system as Windows has become more complex and computer hardware becomes faster and more powerful. The changes Microsoft has made to its files system is charted below on the table below.

Microsoft's file system versions.

FAT12 Represents Microsoft's first file system introduced in 1977, it was provided with Microsoft's Disk BASIC

FAT16 Introduced in 1983 with the release of MS-DOS/PC-DOS 2.0

FAT32 Introduced in 1996 with the release of Windows 95's OEM Service Release 2

NTFS Introduced in July 1993 with the release of Windows NT 3.1

The name FAT is an acronym which stands for File Allocation Table and refers to a table or index listing of file names and clusters. This table is use to centralize the information used to identify which physical areas on the disk that are being used for file storage and which areas are free and available for new file storage. These storage location are commonly referred to cluster addresses, which in essence are sectional divisions mapped onto a physical map of the disk platter.

Microsoft's first file system was developed by Bill Gates and Marc McDonald in 1977 and used for managing disks in a new program called Microsoft Disk BASIC. This file system has become known as FAT12, this beginning file system would later become integrated into a new operating system called 86-DOS, which later became Microsoft's first PC-DOS and MS-DOS.

The table used in the FAT12 file system used a numbering system that was limited to only 12 bits, as a result of this numbering setup the number of clusters that could be used for recording and tracking files was limited to only 4096. While this was enough for the earliest personal computers, improvements in hardware technology very quickly exceeded the limits of the FAT12 file system. The first version of the FAT12 was also limited by its file directories, which simply were not available, the first few versions of the file system only had a root directory available for storing files. The ability to support file directories was added in 1983 with the introduction of MS-DOS 2.0. Another limitation, while not especially a factor with the early storage disks and devices, was the maximum file size in the FAT12 file system, which was limited to only 32MB. (Lowe 2006)

In 1984, Microsoft introduced a major upgraded to their file system, this upgrade would become known as FAT16. FAT16 is best known for increasing the maximum disk size, which was increased from the old maximum of 32MB to a new maximum size of 2GB. FAT16 file system did this by increasing its cluster addressing numbers to 16 bits, which increased the total number of clusters to 65,536.

The final major revision Microsoft made to their FAT file system is known as FAT32, which was introduced in 1996 with the release of Windows 95, the web page www.project9.com pegs FAT32's introduction to the OEM Service Release 2 (OSR2) of Microsoft Windows 95 (commonly known as Windows95b).

Like its predecessors FAT32 is so named because it uses 32-bit numbers to represent clusters, this of course is twice the number size used by FAT16. This dramatically increased the maximum disk size increasing its theoretical maximum size of 2 TB. However, Microsoft has limited the allocation table to only use 28 of the 32 bits. One reason stated for this action was to allow the legacy DOS real-mode to handle the allocation table without creating excessive overhead (The FAT32 Resource Page). Additionally, the Microsoft tools like format.exe and fdisk.exe have limited the disk size to 32GB. There are tools available that will format FAT32 disks up to the 2TB limit. For example, an open source program is available from http://www.ridgecrop.demon.co.uk/index.htm?fat32format.htm which can format the disk to 2TB, and after the disk is formatted Windows XP can access the entire disk space. Another important feature of the FAT32 file system was the introduction of the long file name. Prior to FAT32 file names were limited to the 8.3 file size. The 8.3 file size refers to naming which limited a file name to a maximum of eight