DOS ain't dead

Bug in FreeDOS FDISK 1.3.4 or BIOS? (Developers)

posted by boeckmann, Aachen, Germany, 20.11.2022, 19:09

Hello everyone,

while hacking on Ranish Partition Manager I discovered a strange behaviour of either FreeDOS FDISK or my BIOS, but my guess is FDISK. Perhaps one of you is able to reproduce that:

1) Create a primary partition of 2040 MB using LBA, gets rounded up to 2047 MB.
2) Let FDISK show the partition table: partition is 2047 MB in size
3) close FDISK
4) Open FDISK again and show the partition table: partition is 2055 MB in size
5) Reopen FDISK again with /x command line argument to turn off LBA support: disk is back to 2047 MB in size

Really strange. What is curious even more is that CHS and LBA values in MBR get out of sync. I noticed that because Ranish discovered a MBR inconsistency.

Diagnosis with WDE showed that in the process of editing via FDISK the end cylinder of the partition increased by one. At first it was CHS 260/254/63, after editing (adding a 8000MB extended partition) it was CHS 261/254/63 but LBA sector count remained the same.

Please see the following screenshots that document the behaviour, especially diag_02 and diag_05, which clearly show that the CHS values changed:

https://boeckmann.io/pub/diag_01.jpg
https://boeckmann.io/pub/diag_02.jpg
https://boeckmann.io/pub/diag_03.jpg
https://boeckmann.io/pub/diag_04.jpg
https://boeckmann.io/pub/diag_05.jpg
https://boeckmann.io/pub/diag_06.jpg

Complete thread:

• Bug in FreeDOS FDISK 1.3.4 or BIOS? - boeckmann, 20.11.2022, 19:09
  • Bug in FreeDOS FDISK 1.3.4 or BIOS? - Japheth, 21.11.2022, 08:10
    • Bug in FreeDOS FDISK 1.3.4 or BIOS? - boeckmann, 21.11.2022, 11:21
      • Bug in FreeDOS FDISK 1.3.4 or BIOS? - Laaca, 21.11.2022, 18:21
        • Bug in FreeDOS FDISK 1.3.4 or BIOS? - fritz.mueller, 22.11.2022, 12:06
          • Bug in FreeDOS FDISK 1.3.4 or BIOS? - boeckmann, 23.11.2022, 14:36
            • Bug in FreeDOS FDISK 1.3.4 or BIOS? - tom, 23.11.2022, 16:22
              • Bug in FreeDOS FDISK 1.3.4 or BIOS? - boeckmann, 23.11.2022, 20:23
  • Bug in FreeDOS FDISK 1.3.4 or BIOS? - glennmcc, 23.11.2022, 19:55
    • Bug in FreeDOS FDISK 1.3.4 or BIOS? - boeckmann, 23.11.2022, 20:17
    • Bug in FreeDOS FDISK 1.3.4 or BIOS? - boeckmann, 23.11.2022, 20:52
      • Bug in FreeDOS FDISK 1.3.4 or BIOS? - boeckmann, 24.11.2022, 15:38
        • Bug in FreeDOS FDISK 1.3.4 or BIOS? - fritz.mueller, 24.11.2022, 18:47