MS-DOS 3.3x Extended Partitions Keep Windows from Formatting

• Microsoft Windows operating system versions 3.0, 3.0a, 3.1, 3.11

SYMPTOMS

When trying to format or copy a floppy disk from Microsoft Windows File Manager, you receive one of the following error messages:

   Unable to Format

   -or-

   Unable to Copy

   -or-

   MS-DOS startup disk has an invalid sector size.

CAUSE

Your hard drive may have been formatted with a nonstandard sector size.

This often occurs when a hard drive partitioned larger than 32 MB exists under MS-DOS 3.3x. This can also happen when a third-party disk partitioning program is used.

The standard size for a hard drive sector under MS-DOS is 512K. If the sector size is larger (for example, 1024K), then Windows cannot format a floppy disk from File Manager. This may also affect copying because the destination disk must be formatted.

Under MS-DOS 3.3x, disk partitioning programs like Disk Manager and Speedstor may use larger sectors to allow for larger partitions. This is also prevalent in some original equipment manufacturer (OEM) versions of DOS. OEMs known to have done this are NEC, Zenith, and Wyse. These versions of DOS have an altered FDISK that allows this feature. If there is a partition over 32 MB on an MS-DOS 3.3x system, this is the likely cause of not being able to format or copy disks from File Manager.

NOTE: COMPAQ DOS 3.31 does not have this problem. COMPAQ DOS 3.31 allows larger partitions by allowing for more sectors instead of making larger sectors. This is the same method used in MS-DOS 4.x and later.

WORKAROUND

To work around the problem, try one of the following:

• Repartition the drive using FDISK and keeping the partitions to a size less than 33MB.
• Format and copy disks from the MS-DOS command prompt.
• Upgrade from your OEM's version of MS-DOS to 4.01 or later.