A DOS boot sector written in C
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DOS Boot Sector

This is an x86 boot sector written in C. It is meant to bootstrap a DOS system on a FAT volume. A more detailed explanation of the code is available at https://crimsonglow.ca/~kjiwa/2010/09/dos-boot-sector.html.

View the source. It works like this at a high level:

  • get the drive parameters
  • load the contents of the root directory into memory
  • look for IO.SYS in the root directory
  • load the first 3 sectors of IO.SYS into memory and begin executing it

I've successfully compiled and tested it with the following tools:

  • gcc 4.4.3
  • binutils 2.20.1
  • dosfstools 3.0.7
  • bochs 2.4.2

The gcc and binutils host and target are both i386-pc-elf.

$ make boot      # compile and link the boot sector
$ make io        # compile and link IO.SYS
$ make disk      # create a 10 MB disk image with a FAT volume
$ make deploy    # copy the boot sector and IO.SYS to the disk image
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