Microsoft Corporation Staff, IT Professional Staff - Microsoft Windows 2000 Server Operations Guide

For small volumes, FAT16 or FAT32 usually provide faster access to files than NTFS because:

• The FAT structure is simpler.
• The FAT folder size is smaller for an equal number of files.
• FAT has no controls regulating whether a user can access a file or a folder; therefore, the system does not have to check permissions for an individual file or whether a specific user has access to the file or folder. This advantage is minimal because Windows 2000 still has to determine if the file is read-only, or whether the file is on a FAT or NTFS volume.

NTFS minimizes the number of disk accesses and time needed to find a file. In addition, if a folder is small enough to fit in the MFT record, NTFS reads the entire folder when it reads its MFT record.

A FAT folder entry contains an index of the file allocation table, which identifies the cluster number for the first cluster of the folder. To view a file, FAT has to search the folder structure.

In comparing the speed of operations performed on large folders containing both long and short file names, the speed of a FAT operation depends on the operation itself and the size of the folder. If FAT searches for a file that does not exist, it has to search the entire folder— an operation that takes longer on a FAT structure than on the B-tree structure used by NTFS. In mathematical terms, the average time to find a file on a FAT folder is a function of N/2, where N is the number of files. On an NTFS folder, the average time is a function of Log N.

Several factors affect the speed with which Windows 2000 reads or writes a file:

• Fragmentation of the file. If a file is badly fragmented, NTFS usually requires fewer disk accesses than FAT to find all of the fragments.
• Cluster size. For both file systems, the default cluster size depends on the volume size, and is always a power of 2. FAT16 addresses are 16 bits, FAT32 addresses are 32 bits, and NTFS addresses are 64 bits.
• The default FAT cluster size is based upon the fact that the file allocation table can have at most 65,535 entries, so the cluster size is a function of the volume size divided by 65,535. Therefore, the default cluster size for a FAT volume is almost always larger than the default cluster size for an NTFS volume of the same size. The larger cluster size for a FAT volume means that there might be less fragmentation in files on a FAT volume.
• Location of small files. With NTFS, small files are entirely contained within the MFT record. The file size that fits in the MFT record depends upon the the number of attributes for the file.

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