Maximum Partition Size Using FAT16 File System


Microsoft MS-DOS versions 4.0 and later allow FDISK to partition hard disks up to 4 gigabytes (GB) in size. However, the MS-DOS file allocation table (FAT) file system can support only 2 GB per partition. Because of this fact, a hard disk between 2 and 4 GB in size must be broken down into multiple partitions, each of which does not exceed 2 GB.

NOTE: Windows 95 OEM Service Release version 2 and later support drives larger than 2 GB using the FAT32 file system. For more information about the FAT32 file system, please see the following article in the Microsoft Knowledge Base:

ARTICLE-ID: 154997
TITLE : Description of the FAT32 File System

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The 2-GB partition limit is imposed by the maximum number of clusters and the largest cluster size supported by the FAT file system. The FAT file system is limited to 65,525 clusters. The size of a cluster must be a power of 2 and less than 65,536 bytes--this results in a maximum cluster size of 32,768 bytes (32K). Multiplying the maximum number of clusters (65,525) by the maximum cluster size (32,768) equals 2 GB.

Note that the hard disk drive must be supported by the computer's ROM BIOS APIs, which have a 1024-cylinder limitation, in order for FDISK to partition the hard disk.

Because 32K per cluster can waste valuable hard disk space, the FAT file system is not always the best hard disk management scheme. Microsoft Windows NT uses the NT File System (NTFS), which uses a different file/cluster scheme. Microsoft OS/2 version 1.3 offered HPFS, which also uses a more conservative method of allocating disk resources.

NOTE: Microsoft Windows NT also supports FAT drives. Windows NT 3.51 supports FAT drives up to 4 GB in size. FAT drives from 2 GB to 4 GB in size are not supported by MS-DOS or Windows. In other words, if you wish to have a FAT drive accessible from MS-DOS or Windows 95/98 and Windows NT, your FAT drive should be no larger than 2 GB. If you will be accessing the FAT drive from only Windows NT, then the drive can be 2 GB to 4 GB in size.

For additional information about MS-DOS and Windows drive size and partition limits, please see the following articles in the Microsoft Knowledge Base:

TITLE : FAT Type and Cluster Size Depends on Logical Drive Size

TITLE : MS-DOS Partitioning Summary

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