Deleting Partitions Can Reduce Usable Hard Disk Space (80387)

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

This article was previously published under Q80387


Removing a partition created by a third-party disk-partitioning utility can reduce the total usable space available on the hard disk drive. This problem is most commonly experienced with, but is not limited to, the following systems:
    XT systems with hard disks that are larger than 20 megabytes (MB)
    Systems with hard disks that have more than 1024 cylinders
IMPORTANT: Microsoft cannot guarantee whether or not it is safe to remove a third-party disk partition. If in doubt, contact the manufacturer of your partitioning utility.


Some hard disk drives are not fully supported by the system BIOS. This problem most commonly occurs when the disk uses more heads, cylinders, or sectors per track than is supported by the standard IBM ROM BIOS protocol. The IBM ROM BIOS protocol is limited to 1024 cylinders by 256 heads by 63 sectors per track. Using the standard of 512 bytes per sector, the drive size is limited to 8064 MB (where 1 MB = 1024 x 1024 = 1,048,576 bytes) or 7.875 gigabytes (GB) (where 1 GB = 1024 MB).

This problem also occurs when the system doesn't support the exact combination of heads, cylinders, and sectors per track that the disk uses. As a result, special disk-partitioning utilities have been created that will fully use the hard disks on such systems. Examples of these utilities include the following:
    Disk Manager by OnTrack Software (DMDRVR.BIN, XBIOS.OVL)
    SpeedStor by Storage Dimensions (SSTOR.SYS, HARDRIVE.SYS)
    VFeature Deluxe by Golden Bow Systems (FIXT_DRV.SYS)
    InnerSpace by Priam Systems (EDVR.SYS)
    Everex by Everex Systems (EVDISK.SYS)
Once the partitioning utility has been used to recognize the entire drive, removing the non-MS-DOS partition may result in the hard disk size "shrinking" to what is actually supported by the system ROM BIOS. Returning to full use of the drive usually requires reinstalling the partitioning software. Contact your partitioning software manufacturer for more assistance.

The full hard disk drive can be used without the third-party partitioning software if the system fully supports the hard disk drive. A hard disk drive is generally considered fully supported if it has 1024 or fewer cylinders and the system ROM BIOS was written to correctly recognize it. Even if the hard disk drive has more then 1024 cylinders, the third-party software may not be required if the drive has a translating controller card to translate the real drive parameters to parameters that the ROM BIOS can use.

To determine whether the hard disk drive requires the third-party partitioning utility, refer to the utility's documentation or manufacturer, or possibly the hard disk drive's documentation or manufacturer.

The partitioning utilities included here are manufactured by vendors independent of Microsoft; we make no warranty, implied or otherwise, regarding these product's performance or reliability.

Modification Type: Major Last Reviewed: 11/25/2003
Keywords: KB80387