DOS ain't dead

DOS specifications ("standards") (Developers)

posted by ecm  , Düsseldorf, Germany, 20.11.2020, 16:08

> 3. MBR amendments to support blocks (sectors) above 4G

GPT is right there. I don't think extending the MBR scheme is going to be supported by many implementations.

(For a hack, we could try to support "33 bit LBA" schemes, ie the 32-bit fields for start and length are kept, but it is valid for start and length to *both* be up to FFFF_FFFFh, so (with 512 B/s) a 2 TiB - 512 B FAT32 partition may start at sector FFFF_FFFFh. That is, allowing to use nearly 4 TiB of hard disk space. I'm considering adding that to my early loader (iniload), debugger, and kernel. Most difficult would be the boot sector loaders due to space being at a premium there.)

> 4. large file support (llseek, etc.)

> Where it makes sense, existing specifications should be amended, but some
> things may be better to redo from scratch.

There's FAT+ for FAT32 (and big-cluster FAT16) to store files up to 256 GiB - 1 B in size. (Up from the prior limit of either (commonly) 2 GiB - 1 B or (if using unsigned values) 4 GiB - 1 B). EDR-DOS is the only implementation of this yet.

And here's a description of EDR-DOS's llseek function 7142h. This interface, and corresponding seek offset and size field extensions in the SFTs, allows using 64-bit seeks.

EDR-DOS also allows using a cluster size of "zero" in the BPB byte to mean "256", which (on 512 B/s units) results in 128 KiB clusters. I'm partially supporting that already (in the loaders and debugger), and will add it to the RxDOS kernel eventually.

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l

Complete thread:

• DOS specifications ("standards") - awik, 18.11.2020, 16:57 (Developers)
  • DOS specifications ("standards") - awik, 18.11.2020, 18:48
  • DOS specifications ("standards") - RayeR, 18.11.2020, 20:07
    • DOS specifications ("standards") - awik, 19.11.2020, 13:32
  • DOS specifications ("standards") - glennmcc, 18.11.2020, 20:22
    • DOS specifications ("standards") - awik, 19.11.2020, 13:44
  • DOS specifications ("standards") - Zyzzle, 19.11.2020, 02:23
    • DOS specifications ("standards") - awik, 19.11.2020, 14:02
      • DOS specifications ("standards") - RayeR, 19.11.2020, 19:11
  • DOS specifications ("standards") - Laaca, 19.11.2020, 11:27
    • DOS specifications ("standards") - awik, 19.11.2020, 15:03
    • DOS specifications ("standards") - RayeR, 20.11.2020, 02:04
  • DOS specifications ("standards") - tkchia, 19.11.2020, 14:12
    • DOS specifications ("standards") - awik, 19.11.2020, 15:11
    • DOS specifications ("standards") - RayeR, 19.11.2020, 19:06
  • DOS specifications ("standards") - ecm, 20.11.2020, 16:08
    • DOS specifications ("standards") - awik, 21.11.2020, 16:43
      • DOS specifications ("standards") - tkchia, 21.11.2020, 17:37
        • DOS specifications ("standards") - awik, 21.11.2020, 18:58
          • DOS specifications ("standards") - tom, 22.11.2020, 14:58
      • DOS specifications ("standards") - marcov, 22.11.2020, 22:35
        • DOS specifications ("standards") - RayeR, 23.11.2020, 05:49
      • DOS specifications ("standards") - 33-bit LBA support - ecm, 23.11.2020, 10:01
    • DOS specifications ("standards") - ecm, 25.12.2020, 21:27
  • Hosting/Sharing - rr, 23.11.2020, 21:19
  • DOS specifications ("standards") - Ro2003, 13.01.2024, 09:06
    • DOS specifications ("standards") - awik, 16.01.2024, 11:28
      • DOS specifications ("standards") - jadoxa, 17.01.2024, 02:15
        • DOS specifications ("standards") - Rugxulo, 17.01.2024, 03:40