MS-DOS Partitioning Summary

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SUMMARY
This article contains a summary of MS-DOS partitioning information. Forinformation on how MS-DOS assigns drive letters, please see the followingarticle in the Microsoft Knowledge Base:
51978 Order in Which MS-DOS Assigns Drive Letters
MORE INFORMATION
A hard disk's master boot record (MBR) is located in the first sector ofthe disk (cylinder 0, side 0, sector 1). The partition table is located atoffset 01BE, containing up to four 16-byte entries. The fourth byte ofeach partition table entry is used to mark the partition type.

MS-DOS began supporting hard disks in version 2.0.

MS-DOS Versions 2.x

MS-DOS 2.x supports one type 01 partition of up to 15 megabytes (MB) insize, which uses a 12-bit file allocation table (FAT). Fdisk creates onlyone MS-DOS partition per drive.

MS-DOS 3.0

MS-DOS 3.0 supports partitions larger than 15 MB using a 16-bit FAT, whichallows a smaller cluster size and more efficient disk usage. As a result,MS-DOS 2.x hard disks larger than 15 MB are incompatible with laterversions of MS-DOS. Fdisk creates only one MS-DOS partition per drive.

MS-DOS 3.3

MS-DOS 3.3 introduces support for more than one logical drive per harddisk. Logical drives are treated as completely separate disks underMS-DOS, even though they may occupy the same physical hard disk.

This is supported by using nonbootable MS-DOS partitions known as extendedMS-DOS partitions. Fdisk reports these as EXT DOS; other MS-DOS partitionsare reported as PRI DOS (for primary MS-DOS). Each primary MS-DOSpartition is a logical drive, and extended MS-DOS partitions contain from1 to 23 logical drives (MS-DOS supports drive letters up to Z). Logicaldrives in extended MS-DOS partitions have the same FAT type as a primaryMS-DOS partition of the same size.

Only one PRI DOS partition and one EXT DOS partition is allowed per drive.On computers with two physical hard disks, a PRI DOS partition is notrequired on the second physical disk. A PRI DOS partition is required onthe first physical disk. (MS-DOS does not support more than two physicaldisks.)

MS-DOS 4.0

MS-DOS versions 4.0 and later support logical drives larger than 32 MB.Full usage of these logical drives requires the MS-DOS program Share.exeto be loaded in MS-DOS 4.0.

The following table explains the versions 4.x and later MS-DOS partitiontypes:
   Partition  Fdisk                                    Starting in   Type       Reports      Size            FAT Type    MS-DOS version   ------------------------------------------------------------------   01         PRI DOS      0-15 MB         12-Bit      2.0 (a)   04         PRI DOS      16-32 MB        16-Bit      3.0   05         EXT DOS      0-2 GB (b)      n/a         3.3   06         PRI DOS      32 MB-2 GB (b)  16-bit      4.0				

   (a) 15-MB size limitation extended in version 3.0.   (b) 2 GB (gigabytes) includes a limit of 1024 cylinders per drive       imposed by the standard AT ROM BIOS interrupt 13 protocol.				

MS-DOS 5.0

MS-DOS versions 5.0 and later support up to eight physical hard disks.Share.exe is not required for full large-drive support; this support isincluded in the MS-DOS kernel.

MS-DOS versions 5.0 and later support the same partitioning strategy asversion 4.x, including Fdisk's inability to create more than one primaryMS- DOS partition on a physical disk. However, because some originalequipment manufacturer (OEM) partitioning software allows you to createmore than one primary MS-DOS partition, MS-DOS versions 5.0 and later havekernel support for up to four primary MS-DOS partitions. This makes iteasier to upgrade from previous versions of OEM-modified MS-DOS. Fdiskstill creates only one PRI DOS partition on a physical disk.

NOTE: Many OEMs have changed their versions of MS-DOS to support more thanone primary MS-DOS partition, larger type 04 partitions, and new partitiontypes.

Windows 95

Windows 95 supports two new partition types (0E and 0F) to support thelogical block addressing (LBA) INT13h extensions as specified in theWindows 95 Driver Development Kit (DDK).
   Partition  Fdisk                                    Starting in   Type       Reports      Size            FAT Type    version   ------------------------------------------------------------------   01         PRI DOS      0-15 MB         12-Bit      MS-DOS 2.0   04         PRI DOS      16-32 MB        16-Bit      MS-DOS 3.0   05         EXT DOS      0-2 GB          n/a         MS-DOS 3.3   06         PRI DOS      32 MB-2 GB      16-bit      MS-DOS 4.0   0E         PRI DOS      32 MB-2 GB      16-bit      Windows 95   OF         EXT DOS      0-2 GB          n/a         Windows 95Types 0E and 0F require extended Int13 support.				

NOTE: Type 0E is the same partition type as 06, and 0F is the same as 05.However, applications should use the (LBA) INT13h extension's read/writefunctions to read from or write to the drive instead of the normalCylinder/Head/SectorPerTrack (CHS) INT13h functions because the hard diskhas more than 1024 cylinders and/or more than 16,711,680 sectors. Notethat earlier versions of FDISK recognize these Windows 95 partitions asNON-DOS partitions.

Windows 95 OEM Service Release 2 and Windows 98

Windows 95 OEM Service Release 2 (OSR2) and Windows 98 support two newpartition types (0B and 0C) to support the FAT32 file system. Foradditional information about FAT32, please see the following article inthe Microsoft Knowledge Base:
ARTICLE ID: 154997
TITLE : Description of the FAT32 File System

The partition types supported by OSR2 and Windows 98 are as follows:
   Partition  Fdisk                                          Starting in   Type       Reports      Size                  FAT Type    version   ---------------------------------------------------------------------   01         PRI DOS      0-15 MB               12-Bit      MS-DOS 2.0   04         PRI DOS      16-32 MB              16-Bit      MS-DOS 3.0   05         EXT DOS      0-2 GB                n/a         MS-DOS 3.3   06         PRI DOS      32 MB-2 GB            16-bit      MS-DOS 4.0	   0E         PRI DOS      32 MB-2 GB            16-bit      Windows 95   0F         EXT DOS      0-2 GB                n/a         Windows 95   0B         PRI DOS      512 MB - 2 terabytes  32-bit      OSR2   0C         EXT DOS      512 MB - 2 terabytes  32-bit      OSR2Types 0E, 0F, and 0C require extended Int13 support.				



2.x 3.00 3.10 3.30 3.30a 4.00 4.01 4.01a 5.00 5.00a 6.00 6.20 6.21 6.22 msdos
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Article ID: 69912 - Last Review: 12/04/2015 09:06:51 - Revision: 3.0

Microsoft Windows 95, Microsoft Windows 98 Standard Edition

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