Clusters (Allocation Units)
As described
here, the smallest unit of space on the
[COLOR=blue! important][COLOR=blue! important]hard [COLOR=blue! important]disk[/color][/color][/color] that any software can access is the
sector, which normally contains 512 bytes. It is possible to have an allocation system for the disk where each file is assigned as many individual sectors as it needs. For example, a 1 MB file would require approximately 2,048 individual sectors to store its data. The file system
HPFS uses this type of arrangement.
http://www.pcguide.com/ref/hdd/file/clustClusters-c.html
SUMMARY
loadTOCNode(1, 'summary');This article describes and lists the default values that Windows XP uses to format a volume. The article lists default values for both the NTFS file system and the file allocation table (FAT) file system.
MORE INFORMATION
loadTOCNode(1, 'moreinformation');All file systems that Windows XP uses to organize the hard disk are based on cluster (allocation unit) size, which represents the smallest amount of disk space that can be allocated to hold a file. The smaller the cluster size, the more efficiently your disk stores information.
If you do not specify a cluster size for formatting, Windows XP Disk Management bases the cluster size on the size of the volume. Windows XP uses default values if you format a volume as NTFS by either of the following methods: •By using the
format command from the command line without specifying a cluster size.•By formatting a volume in Disk Management without changing the
Allocation Unit Size from
Default in the
Format dialog box. The following table shows the default values that Windows XP uses for NTFS formatting. Drive size (logical volume) Cluster size Sectors ---------------------------------------------------------- 512 MB or less 512 bytes 1 513 MB - 1,024 MB (1 GB) 1,024 bytes (1 KB) 2 1,025 MB - 2,048 MB (2 GB) 2,048 bytes (2 KB) 4 2,049 MB and larger 4,096 bytes (4 KB) 8
http://support.microsoft.com/kb/314878/