Maximum Partition Size in MS-DOS

Last reviewed: December 15, 1997
Article ID: Q118335

4.00 4.01 5.00 6.00 6.20 6.21 6.22 MS-DOS kbsetup kbhw

The information in this article applies to:

Microsoft MS-DOS operating system versions 4.x, 5.0, 6.0, 6.20, 6.21, 6.22

SUMMARY

Microsoft MS-DOS versions 4.0 and later allow FDISK to partition hard disk drives 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 drive between 2 and 4 GB in size must be broken down into multiple partitions, each of which does not exceed 2 GB.

MORE INFORMATION

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 95. In other words, if you wish to have a FAT drive accessible from MS-DOS or Windows 95 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, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q127851
   TITLE     : Problems Accessing Windows FAT Drives Larger than 2 GB

For additional information about MS-DOS and Windows 95 drive size and partition limits, please see the following articles in the Microsoft Knowledge Base:

   ARTICLE-ID: Q67321
   TITLE     : FAT Type and Cluster Size Depends on Logical Drive Size

   ARTICLE-ID: Q69912
   TITLE     : MS-DOS Partitioning Summary

KBCategory: kbsetup kbhw
KBSubcategory: msdos
Additional reference words: 4.0 4.00 4.01 5.0 5.00 6.00 6.20 win95
Keywords : msdos kbhw kbsetup
Version : 4.00 4.01 5.00 6.00 6.20 6.21 6.
Platform : MS-DOS

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Last reviewed: December 15, 1997
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