Assembly Language

Every high-level line of code you write eventually becomes this — raw instructions the CPU executes directly. Most engineers never see it. The ones who do understand what the machine is really doing, and why performance work is never guesswork.

Python — what you write
def factorial(n):
  if n == 1:
    return 1
  return n * factorial(n-1)
 
factorial(5) # → 120
x86-64 Assembly — what runs
; factorial(5)
MOV RAX, 5  ; n=5
MOV RBX, 1  ; result
.loop:
  IMUL RBX, RAX
  DEC RAX
  JNZ .loop
; RBX = 120
RAX0x0000000000000001done
RBX0x0000000000000078= 120