🖥️ 64-bit Assembly & Registers (x86-64)

Modern desktop and server CPUs use the 64-bit extension of the x86 architecture, often called x86-64 or AMD64. It vastly expands register sizes and count compared to 32-bit (x86), letting programs work with larger data and address more memory directly.

In 64-bit assembly, you’ll mostly use registers like rax, rbx, rcx, and so on — these are 64-bit registers that replace the old 32-bit eax, ebx, ecx, etc. You can still access lower 32, 16, and 8-bit parts of these registers for backwards compatibility, but the 64-bit parts are the main deal now.

📚 Example Code: Simple Addition

section .text
global _start

_start:
    mov rax, 10       ; Load 10 into rax (64-bit register)
    mov rbx, 5        ; Load 5 into rbx
    add rax, rbx      ; rax = rax + rbx (15)

    ; Exit syscall (Linux x86-64)
    mov rdi, 0        ; status code 0
    mov rax, 60       ; sys_exit
    syscall

💡 Pro Tip: Registers like rax are versatile — used for return values, math, and syscalls. Mastering them is key to 64-bit asm.