Assembly

Assembly language is a low-level programming language that has a strong correspondence between its instructions and the architecture's machine code instructions. It is specific to a particular computer architecture and is one level above machine code, which is directly executed by the CPU.

Assembly language uses mnemonic codes or symbols (instead of binary code) to represent the fundamental instructions that the CPU can understand and execute. This makes it more readable for humans compared to raw machine code. Each type of CPU has its own specific assembly language. For example, the assembly language for an Intel processor is different from that of an ARM processor.

It provides direct control over the hardware, allowing programmers to optimize operations for speed and efficiency, manipulate hardware directly, and write code for system bootstraps and device drivers. Assembly language consists of an instruction set, which includes operations like moving data, branching, and arithmetic/logic operations. Each instruction generally has an opcode (operation code) and operands (the data to be processed).

A simple example of an assembly language program is as follows, which adds two numbers on an x86 processor:

section .data
    num1 db 5          ; Define byte 'num1' with value 5
    num2 db 3          ; Define byte 'num2' with value 3
    result db 0        ; Define byte 'result' to store the result

section .text
    global _start

_start:
    mov al, [num1]     ; Move the value of 'num1' into register AL
    add al, [num2]     ; Add the value of 'num2' to the value in AL
    mov [result], al   ; Move the result back into 'result'

    ; Exit the program
    mov eax, 1         ; System call number for 'exit'
    mov ebx, 0         ; Exit code
    int 0x80           ; Interrupt to signal the kernel

This program performs the following steps:

  • Stores two numbers in memory (num1 and num2).
  • Loads the first number into a register (AL).
  • Adds the second number to the register.
  • Stores the result back in memory (result).
  • Finally, it exits the program by making a system call.

Assembly language allows for highly efficient and performance-optimized coding, ideal for time-critical and resource-limited systems. Writing and maintaining assembly code is more complex and time-consuming than using high-level languages. It requires a deep understanding of the specific hardware architecture.

Today, it's often used in embedded systems, device drivers, real-time systems, and critical sections of code in larger applications where performance is paramount. Most software development, however, is done in higher-level languages due to their greater abstraction and portability.