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    Disks and Clusters

The following tables illustrate below the various cluster size limitations for each particular file systems. Why should you care about the cluster size of your partition? You can save a great deal of space by choosing the right file system. For example, if your file is 1K in size and your cluster size is 32K, then you've just wasted 31K of "slack" space for that file.
All file systems used by Windows NT organize your hard disk based upon cluster (or allocation unit) size, which represents the smallest amount of disk space which can be allocated to hold a file. So when file sizes do not come out to an even multiple of the cluster size, extra space must be used to hold the file (up to the next multiple of the cluster size). On the typical partition, this means that (cluster size)/2 * (number of files) worth of space is lost this way. 
 

    FAT/FAT16 (DOS/Windows 95a\Windows NT)

Partition Size Cluster Size
0 - 127MB 2K
128 - 255MB 4K
256 - 511MB 8K
512 - 1023MB 16K
1024 - 2047MB 32K

 Note: FAT16 is limited to 2GB per partition. 
 

    FAT32 (Windows 95b\95c\98)

Partition Size Cluster Size
512MB or less*** 4K***
513MB - 1024MB (1GB) 4K
1025MB - 2048MB (2GB) 4K
2049MB - 4096MB (4GB) 4K
4097MB - 8192MB (8GB) 4K
8GB - 16GBB 8K
16GB - 32GB 16K
32GB or more 32K

 In order to use FAT32 on a Windows computer you must use FDISK to enable Large Disk Support.
Note: A partition formatted as FAT32 can only been seen in Windows 95 version 950B/950C or Windows 98. Eariler versions of Windows 95, DOS 6.22, or even Windows NT 4.0 cannot recognize FAT32 partitions! 
*** If the partition is less than 512mb in size Dos will format to FAT16 if you answered NO to Supporting Large Disks during FDISK. 
 

    NTFS (Windows NT)

Partition Size Sectors/Cluster Cluster Size
512MB or less 1 512 bytes
513MB - 1024MB (1GB) 2 1K
1025MB - 2048MB (2GB) 4 2K
2049MB - 4096MB (4GB) 8 4K
4097MB - 8192MB (8GB) 16 8K
8193MB - 16,384MB (16GB) 32 16K
16,385MB - 32,768MB (32GB) 64 32K
32GB or more 128 64K

 If no cluster size is specified during format, NTFS picks defaults based upon the size of the partition. These defaults have been selected to reduce the amount of space lost and to reduce the amount of fragmentation on the partition.
To specify allocation unit sizes at Format use : format /a:<size>
Note: You cannot use NTFS file compression if your cluster size is larger than 4K. 
 

    In Summary

  FAT FAT32 NTFS
Partition Size Cluster Size Cluster Size Cluster Size
512MB or less 8K or less 4K 512 bytes
513MB - 1024MB (1GB) 16K 4K 1K
1025MB - 2048MB (2GB) 32K 4K 2K
2049MB - 4096MB (4GB)   4K 4K
4097MB - 8192MB (8GB)   4K 8K
8193MB - 16,384MB (16GB)   8K 16K
16,385MB - 32,768MB (32GB)   16K 32K
32GB or more   32K 64K

 

Try this link for more information: http://www.pcguide.com/ref/hdd/file/part-i.htm