Re: [Freedos-user] DOs, or open source boot loaders?

[tom e. <te...@dr...>]

Hallo Herr Roger via Freedos-user,

am Dienstag, 31. März 2026 um 17:21 schrieben Sie:

>> On Sun, Mar 29, 2026 at 06:45:37PM -0400, Karen Lewellen via Freedos-user wrote:
>>My question was weather freedos has its own boot loader application.  That is
>>how freedos is related.


> Boot sequence of legacy BIOS with MBR formated storage media (eg. hard
> drive with formated MBR partition structures); 1) BIOS looks for MBR
> activate partition, 2) BIOS then looks for executable boot code, for
> example DOS IO.SYS/MSDOS.SYS, FreeDOS FDCONFIG.SYS/CONFIG.SYS, are then
> loaded into memory and executed.

Unfortunately this is complete nonsense.

1) BIOS reads the first sector (512 Byte) on the disk and executes it.

2) This code scans the partitiontable (part of the 512 Byte) for an active
partition, then reads *this* sector and executes it. the MBR.

3) This sector - which is probably different for FAT12, FAT16, FAT32, EXTFS filesystems
  and OS. E.g. FreeDOS searches for "KERNEL.SYS", MSDOS searches for IO.SYS, loads it
  and executes it.

4) KERNEL.SYS is then responsible to locate FDCONFIG.SYS and FDAUTO.BAT, COMMAND.COM.

 


> A decent DOS start execution process explanation can be found here:

> DOS DAYS, "A Guide to DOS Startup Files"
> https://www.dosdays.co.uk/topics/dos_startup.php

only 50% accurate, unfortunately.

> As for Rockbox, Rockbox hooks into the OEM firmware/bootloader loading
> process.

> Roger






Mit freundlichen Grüßen / with kind regards
Tom Ehlert
+49-15151898538