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Book8088's CF2IDE stumps Freedos boot (Users)

posted by samwdpckr, 04.02.2024, 05:27

> > XT-class BIOSes don't usually support LBA, so the DOS kernel has to use
> CHS
> > to access the sectors on the disk.
> >
> > Many DOS implementations (probably at least FreeDOS and MS-DOS, not
> sure)
> > detect the disk geometry from the information in the FAT boot sector, so
> > you cannot just write any random filesystem image to the SD card with
> > Linux's dd command and expect it to work properly.
> >
> > When creating the filesystem you need to use the same geometry that the
> > Book8088's BIOS uses.
> >
> > At least MS-DOS and FreeDOS also require that the disk is partitioned.
> The
> > starting sectors of the partitions in the partition table also need to
> be
> > compatible with the actual geometry.
>
> you can test it with 86box, with 8088 machine with XT-IDE and a disk image
> with CHS=1006/16/63, partitioned and formatted with DOS 3.31, and boot with
> FreeDOS 2043-86 kernel (F16/F32 doesn't matter) and you can get same
> error:
> [image]
> (I even tried latest snapshot uploaded in github, but it makes no
> difference)
There may also be something wrong with FreeDOS. I noticed that for some reason ST-DOS's partition mounter can parse logical partitions that are created with MS-DOS 6.22, but it has problems parsing logical partitions that are created with FreeDOS. FreeDOS is probably not fully following the specification of the MS-DOS partition table. FreeDOS doesn't have problems parsing partition tables that are created with its own FDISK though.

FreeDOS is clearly doing something differently than MS-DOS, but I haven't investigated what exactly is the difference.

Different versions of MS-DOS also create different partition tables and parse them differently, and they may not be 100% compatible with each other. MS-DOS 3.31 is a relatively old version, and FreeDOS only aims to be compatible with MS-DOS 6.22.

I recommend at least creating the partition tables and filesystems with the same operating system that is going to use them.

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