OS_from_Scratch

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The main objective of the project is to implement a bootable OS with the help of "How to Write an Operating System from Scratch?" by Nick Blundell.

The README is incomplete!!!! Please run the following from command line to get a demo of what it does :

$ nasm boot_sect.asm -f bin -o boot_sect.bin
$ sudo-apt get install qemu
$ qemu-system-x86_64 boot_sect.bin

(Optional) If you wish to see the binary contents of the boot_sector:

$ od -t x1 -A n boot_sect.bin

The boot_sector code(mostly in assembly language) is as follows :

• boot_sect.asm :

  • The entry point to seize control of the Computer
  • The boot sector is implemented in protected mode.
  • The last two bytes of the 512-byte sector are set to the magic number 0xaa55, to indicate itself to BIOS

• disk_load.asm :

  • Reading more data from the disk will be essential for boot-strapping our operating system,
  • Reading the first N sectors following the boot sector from a given disk
  • Reading from dh Sector of ch cylinder.

• gdt.asm

  • The Global Descriptor Table

• switch_to_pm.asm :

  • Switch off interrupts(CLI)
  • Load Global Descriptor Table(gdt)
  • Jump to Code Segment
  • Update Stack Pointer
  • Begin Protected Mode.

• print_string.asm : printing a string in real mode

• print_string_pm.asm : printing a string in protected mode