When Not to Use MS-DOS 5.0 CHKDSK and UNDELETE Commands

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The Microsoft MS-DOS CHKDSK and UNDELETE commands dated 04/09/91, which areincluded in the Microsoft MS-DOS 5 Upgrade, do not work correctly onlogical drives that require 256 sectors to store each copy of the fileallocation table (FAT). If any of the partitions on your hard disk driveare within the ranges listed in the following section and you do not haveversion 5.0a of the Microsoft MS-DOS 5 Upgrade, which includes CHKDSK.EXEand UNDELETE.EXE files dated 11/11/91, obtain the new CHKDSK and UNDELETEfile.
127 MB - 129 MB
254 MB - 258 MB
508 MB - 516 MB
1018 MB - 1030 MB
2035 MB - 2061 MB
If your FAT occupies 256 sectors, using the CHKDSK.EXE file dated 04/09/91with the /f parameter ("chkdsk /f" [without the quotation marks]) canresult in data loss. Using the UNDELETE.EXE file dated 04/09/91 can lead tounpredictable results.

Microsoft has confirmed this to be a problem in MS-DOS version 5.0. Thisproblem was corrected in MS-DOS version 5.0a.
Drives that require a 256-sector FAT occur when the disk is close to 128MB, 256 MB, 512 MB, or 1024 MB. The closeness to these limits increases asthe drive size increases. For example, "close to 128 MB" is within 0.25 MBof 128 MB and "close to 256 MB" is within 0.74 MB of 256 MB.

Determining If You Need to Install the Updated Files

Drives require a 256-sector FAT if they have partitions within the sizeranges listed below. Because the potential problems are serious, theseranges include a margin of safety.
127 MB - 129 MB
254 MB - 258 MB
508 MB - 516 MB
1018 MB - 1030 MB
2035 MB - 2061 MB
You can use the Fdisk program to determine if you have a 256-sector FATwith the following procedure:

  1. At the MS-DOS command prompt, type the following and press the ENTER key:
  2. Press 4 on the keyboard to select the Display Partition Information option and press ENTER.
  3. The primary partition size is listed under the Mbytes heading. If the size falls within any of the ranges specified above, obtain the updated CHKDSK.EXE and UNDELETE.EXE files.
  4. If you have an extended partition, press the ENTER key to view those partition sizes. If any of the extended partition sizes listed under the Mbytes heading fall within the ranges specified above, obtain the CHKDSK.EXE and UNDELETE.EXE files.
  5. Press the ESC key twice to exit to the MS-DOS command prompt.

"MS-DOS Functions Quick Reference," Ray Duncan, Microsoft Press, MicrosoftCorporation

"QUE DOS Programmer's Reference," Terry Dettman, QUE Corporation

"MS-DOS 5.0 Programmer's Reference," Microsoft Press, MicrosoftCorporation, page 315
appnote 5.00

Article ID: 80496 - Last Review: 12/04/2015 09:11:45 - Revision: 1.1

Microsoft MS-DOS 5.0 Standard Edition

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