Windows File System Comparison

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Introduction

Microsoft's famed Windows platforms are operating systems that are used on personal computers, servers, and varied media devices. There are several platforms that serve each of these environments. Windows XP is an operating systems oriented for desktop computers. Windows Server 2003 is a platform for hosting enterprise-wide server systems. Windows Mobile is the operating system of choice for Pocket PC enabled devices. With such a diverse portfolio, Microsoft has captured a majority of the personal computer market.

FAT

The FAT (File Allocation Table) file system has its origins in the late 1970s and early1980s and was the file system supported by the Microsoft MS-DOS operating system (Wikipedia-1). It was originally developed as a simple file system suitable for floppy disk drives less than 500K in size. Over time it has been enhanced to support larger and larger media. Currently there are three FAT file system types: FAT12, FAT16 and FAT32. The basic difference in these FAT sub types, and the reason for the names, is the size, in bits, of the entries in the actual FAT structure on the disk. There are 12 bits in a FAT12 FAT entry, 16 bits in a FAT16 FAT entry and 32 bits in a FAT32 FAT entry.

The first important data structure on a FAT volume is called the BPB (BIOS Parameter Block), which is located in the first sector of the volume in the Reserved Region (Pollard, 2006). This sector is sometimes called the "boot sector" or the "reserved sector" or the "0th sector," but the important fact is simply that it is the first sector of the volume. The BPB in the boot sector defined for MS-DOS 2.x only allowed for a FAT volume with strictly less than 65,536 sectors (32 MB worth of 512-byte sectors). This limitation was due to the fact that the "total sectors" field was only a 16-bit field. This limitation was addressed by MS-DOS 3.x, where the BPB was modified to include a new 32-bit field for the total sectors value. The next BPB change occurred with the Microsoft Windows 95 operating system, where the FAT32 type was introduced. FAT16 was limited by the maximum size of the FAT and the maximum valid cluster size to no more than a 2 GB volume if the disk had 512-byte sectors. FAT32 addressed this limitation on the amount of disk space that one FAT volume could occupy so that disks larger than 2 GB only had to have one partition defined.

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