DOS ain't dead - Bug confirmed

Bug confirmed (Users)

posted by tom , Germany (West), 03.01.2021, 15:45

> I again played a bit with FD fdisk. Here's again the 2 overlapping
> partitions:
>
> > type start sec size abs. sectors > > FAT32,LBA 390703104 16777216 8192 390703104-407480319 > > FAT32,LBA 407472660 16787925 8197 407472660-424260584 >

is it correct that the 1st partition was created by linux, the 2nd by FDISK?

>
> Now, one missing information is the geometry returned by Int 0x13,
> ah=0x48:
>
> Cyl/Head/Sec=121601/255/63
>
> This gives a good hint where the problem is:
>
> 1. Multiplying "heads" and "sectors": 255x63=16065
> 2. Dividing the 2. start sector thru this value: 407472660/16065=25364
>
> The division has no remainder. And so I conclude: FD fdisk tries to align
> the partition's start sector (and size) to a "cylinder" boundary, either
> rounding or skipping remainders. This indeed works - as long as FD fdisk
> handles the MBR exclusively. Linux fdisk, however, doesn't seem to care
> about cylinder boundaries, at least not if the partition type is
> FAT32-LBA.

most likely correct; DOS for historical reasons aligns partitions on track boundaries, linux and newer windows on 4K or 1M boundaries.

of course this is a FDISK bug; it should round up the 1st partition and not down.

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Complete thread:

Current FreeDOS fdisk utility - Japheth, 01.01.2021, 20:51
- Current FreeDOS fdisk utility - RayeR, 01.01.2021, 23:45
  - Current FreeDOS fdisk utility - Japheth, 02.01.2021, 02:54
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        Forum monospaced font bug - ecm, 06.01.2021, 16:54
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- Current FreeDOS fdisk utility - rr, 02.01.2021, 12:50
  - Current FreeDOS fdisk utility - other FreeDOS bugs and fixes - mceric, 02.01.2021, 16:13
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      - Current FreeDOS fdisk utility - other FreeDOS bugs and fixes - mceric, 02.01.2021, 20:23
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        Current FreeDOS fdisk utility - other FreeDOS bugs and fixes - mceric, 10.01.2021, 00:40
- Current FreeDOS fdisk utility - Japheth, 02.01.2021, 15:39
- Current FreeDOS fdisk utility - marcov, 02.01.2021, 16:56
- Bug confirmed - Japheth, 03.01.2021, 11:16
  - Bug confirmed - tom, 03.01.2021, 15:45
    - Bug confirmed - Japheth, 03.01.2021, 20:40
  - Bug confirmed - tom, 06.01.2021, 17:31
    - Bug confirmed - Japheth, 06.01.2021, 18:16
      - Bug confirmed - RayeR, 16.01.2021, 05:14
        Bug confirmed - tom, 16.01.2021, 12:01
    - Bug confirmed - rr, 07.01.2021, 23:48
- Current FreeDOS fdisk utility - tom, 10.01.2021, 19:10
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