How Code Runs
You write code in a programming language that humans can read. But CPUs only understand machine code — simple binary instructions. Something has to bridge that gap.
The Execution Pipeline
When you run a program, your code goes through a transformation:
- Your code (human-readable text)
- Processing (translation or interpretation)
- Machine code (binary instructions)
- CPU execution (actual computation)
Think of it like reading instructions step by step. Someone wrote directions in English, but the person following them needs to understand each step before acting. The computer "reads" your code and converts it into actions.
Two Approaches to Running Code
There are two main ways code gets executed:
Interpreted languages (like Python and JavaScript) use an interpreter that reads your code line by line, translating and executing each instruction as it goes. It's like having a live translator who speaks each sentence as they hear it.
Compiled languages (like C and Go) use a compiler that translates your entire program into machine code before anything runs. It's like translating an entire book before anyone reads it.
Both approaches get your code running — they just take different paths to get there.
The Runtime Environment
Code doesn't run in isolation. It needs a runtime — an environment that provides essential services like memory management, access to files, and network capabilities.
When you run a Python script, the Python runtime handles all the behind-the-scenes work. When JavaScript runs in a browser, the browser's JavaScript engine serves as the runtime.
What Happens During Execution
As your code runs, the CPU:
- Loads instructions from memory
- Performs calculations
- Stores results
- Moves to the next instruction
This happens billions of times per second. Your simple print("Hello") statement triggers thousands of low-level operations.
Why This Matters
Understanding execution helps you debug problems. When code crashes, knowing that it runs sequentially helps you trace where things went wrong. It also explains why some programs start instantly (already compiled) while others take a moment (being interpreted).