What Are System Calls?

System calls are special requests your program makes to the operating system (OS) to do things like print text, read files, or exit.

Using System Calls in NASM

On Linux, you:

• Set up arguments in registers (like eax, ebx, ecx)
• Use the int 0x80 instruction to ask the OS to help

Example: Printing to the Screen

mov eax, 4          ; syscall number for write
mov ebx, 1          ; file descriptor 1 = stdout
mov ecx, message    ; pointer to your message
mov edx, 13         ; message length
int 0x80            ; make the call

Why This Matters

System calls connect your NASM programs to the real world: files, screens, keyboards, and more!

Learning to use them is essential for any non-trivial app.