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WDe and GPT, booting DOS (Users)

posted by Japheth Homepage, Germany (South), 02.11.2022, 07:55

> Using WDE in FreeDOS I have saved the first 3 sectors of the MBR to a file
> (called 3sectors).
First you should make yourself familiar with the difference of MBR ( the boot sector of the DISK ) and a FAT32 "boot sector".

Some details where FD may differ from MS-DOS:

- the MS-DOS kernel is named IO.SYS.
- the boot code of DOS71BSG.BIN loads IO.SYS at 0070:0000
- the boot code loads just the first 4 sectors of IO.SYS.
- the boot code checks four bytes of loaded IO.SYS ( at pos 0 and pos 200h )
- the boot code loads SI:DI with the start cluster of IO.SYS
- the boot code of MS-DOS jumps to 0070:0200 to switch control to the kernel
- when jumping, there are a few values on the stack that IO.SYS might use.

So there's pretty much that may go wrong when using DOS71BSG for FreeDOS...:-D

---
MS-DOS forever!

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