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I made my own DOS implementation (Announce)

posted by samwdpckr, 08.12.2023, 22:11

> if you search the FreeDOS kernel for #ifdef FAT32 you should get an idea
> what to change for FAT32 support. it's surprisingly little differenz.
 FAT32 is very similar to FAT12/16, but I would implement it as a dynamic filesystem driver. The static filesystem driver in the kernel binary supports only FAT12/16.

> "4k native": drives that present the internal 4k sector size - which is
> normal in modern disks - as 4K to the external world. Most disks emulate a
> 512 byte sectorsize, even modern ones.
The kernel should support different sector sizes, but it is hard to test.

> adding GPT support should be easy. actually GPT partitioning is easier then
> MBR due to the (slightly complicated) extended partitions.
> GPT has only primary partitions.
 I know, but GPT is also very limited.

> > I have designed my own partitioning scheme
> > that supports unlimited number of partitions, but haven't implemented it
> > yet.
> Don't do that. use GPT.
 Why not?

> AFAIK BIOS int13h extensions are implemented as 48-bit indexing in
> the year 2023.
 Of course, but the API uses 64-bit numbers. Only the physical implementation has only 48 bits.

> Good luck on your project, and thanks for sharing with the community.
 Thanks.


> Thanks for the explanation and, as your kernel seems to be using RAW
> sector-offsets, sector size shouldn't matter as to whether it's 512-byte
> native, 512-byte "emulated", or 4k-byte native.
 Some medias, for example optical disks, use larger sectors that cannot be emulated as smaller 512 byte sectors. Optical disks usually use sector size of 2 kB. Also floppies can have different sector sizes, and everything from 128 bytes to 1 kilobyte is commonly used. Floppies are always soft sectored and BIOS cannot do logical block addressing with them.

> Never mind, of course there is not 2 TB limit when using UEFI int 13
> extensions. I was confusing the old DOS/BIOS 2TB limit and direct 64-bit
> index calls to int 13h.
This has nothing to do with UEFI.

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