Communicating with the OS

Assembly programs often need to perform actions like reading files or printing output. This is done by making system calls to the operating system.

How System Calls Work

You load specific values into registers (like eax, ebx) to tell the OS what you want, then trigger a software interrupt (like int 0x80 on Linux).

mov eax, 1      ; syscall number for exit
xor ebx, ebx    ; exit code 0
int 0x80        ; invoke syscall

Common System Calls

• write: Output to console or file
• read: Input from console or file
• exit: End the program

Real-World Impact

System calls are the foundation for all applications, from simple scripts to complex browsers, as they allow software to interact with hardware safely.