FAT Type and Cluster Size Depends on Logical Drive Size (67321)
The information in this article applies to:
• Microsoft MS-DOS operating system 3.1
• Microsoft MS-DOS operating system 3.2
• Microsoft MS-DOS operating system 3.21
• Microsoft MS-DOS operating system 3.3
• Microsoft MS-DOS operating system 3.3a
• Microsoft MS-DOS operating system 4.0
• Microsoft MS-DOS operating system 4.01
• Microsoft MS-DOS operating system 5.0
• Microsoft MS-DOS operating system 5.0a
• Microsoft MS-DOS operating system 6.0
• Microsoft MS-DOS operating system 6.2
• Microsoft MS-DOS operating system 6.21
• Microsoft MS-DOS operating system 6.22
• Microsoft Windows 95
This article was previously published under Q67321
SUMMARY
MS-DOS allocates disk space for files in units of one or more sectors;
these units are called "clusters" or "allocation units." On any MS-DOS
disk, a 1-byte file is allocated 1 cluster of disk space, wasting the
unused area of the cluster. A file that is 3.2 clusters large is given
4 clusters. Overall, a smaller cluster size means less waste.
The cluster size for a drive is decided by FORMAT, depending on the
size of the logical drive (see table, below). "Logical drive" refers
to an MS-DOS volume accessed by a drive letter (A:, B:, C:, D:, and so
forth). Hard disk users may want to consider cluster size when
choosing how to partition their drive(s).
The cluster size of a floppy drive cannot be changed. The cluster size
of a hard drive can be changed only by changing the size of the
logical drive, which is done by repartitioning the hard drive.
CHKDSK displays the allocation unit size for a logical drive. FDISK's
option 4 displays the size(s) of logical drives on the hard drive(s).
NOTE: DoubleSpace-compressed drives appear to have 8K clusters, but
internally vary the sectors-per-cluster as necessary (this information
is recorded in the MDFAT). For example, a 10K file which compresses
by a factor of 2:1 actually uses 5K, or 10 sectors, of drive space.
Modification Type: |
Major |
Last Reviewed: |
5/12/2003 |
Keywords: |
KB67321 |
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