== Instruction ==

Build with nasm -f bin mbr.asm -o mbr

Run with qemu-system-x86_64 -boot a -fda mbr

Debug with qemu-system-x86_64 -boot a -fda mbr -s -S gdb target remote localhost:1234 layout asm b *0x7c00 c

== ASM reg ==

=== In 16 bits === There is 4 main 16bits reg: AX, BX, CX, DX. You can access the 8 MSB from AX with AH and the 8 LSB with AL.( BH,BL, CH, CL)

SI and DI are 16bits index register often used for pointer but can contains data.

SP is stack pointer, BP is base pointer

AX(AH, AL), BX(BH, BL), CX(CH, CL), DX(DH, DL), SI, DI, SP, BP

=== In 32bits === Main register are "Extended" to 32bits but 16bits of 8bits direct access is not possible anymore.

EAX, EBX, ECX, EDX, ESI, EDI, ESP, EBP

=== In 64bits === Prefixed by R RAX, RBX, RCX, RDX, RSI, RDI, RSP, RBP

== Bios Memory ==

0x0 - 0x03FF ;IVT 0x400 - 0x4FF ;BIOS Data 0x500 - 0x7BFF ;Unused 0x7C00 - 0x7D77 ;Bootloader 0x7E00 - 0x9FFFF ;Unused 0xA0000 - 0xBFFFF ;Video memory 0xB0000 - 0xB7777 ;Video memory monochrome 0xB8000 - 0xBFFFF ;Video memory color 0xC0000 - 0xC7FFF ;BIOS ROM 0x80000 - 0xEFFFF ;BIOS shadow memory 0xF0000 - 0xFFFFF ;BIOS System

== Interrupt Vector Table ==

INT_NUM	Short Description PM
0x00	Division by zero
0x01	Debugger
0x02	NMI
0x03	Breakpoint
0x04	Overflow
0x05	Bounds
0x06	Invalid Opcode
0x07	Coprocessor not available
0x08	Double fault
0x09	Coprocessor Segment Overrun (386 or earlier only)
0x0A	Invalid Task State Segment
0x0B	Segment not present
0x0C	Stack Fault
0x0D	General protection fault
0x0E	Page fault
0x0F	reserved
0x10	Math Fault
0x11	Alignment Check
0x12	Machine Check
0x13	SIMD Floating-Point Exception
0x14	Virtualization Exception
0x15	Control Protection Exception

== BIOS IRQ == https://en.wikipedia.org/wiki/BIOS_interrupt_call