OS Fundamentals — What Even Is an OS?
Starting with the basics — an OS is software, not hardware, and programs run through a Fetch → Decode → Execute cycle.
I'm starting with OS fundamentals — the building blocks everything else sits on.
What even is an OS?
An operating system is software, not hardware. It's the layer that sits between your programs and the physical machine, making it easier to run code without every developer having to talk directly to the CPU, memory, and disks.
Without an OS, every program would need to know how to manage hardware itself. With one, you get a clean interface: write your program, run it, and the OS handles the messy details.
Programs and instructions
When a program runs, it executes millions or billions of instructions per second — a staggering pace. Each instruction is a tiny operation, something as simple as add two values or load a value from memory.
Those instructions live in memory. The processor fetches them, one after another, and runs them.
The Fetch → Decode → Execute cycle
This is the heartbeat of every CPU:
- Fetch — grab the next instruction from memory
- Decode — figure out what the instruction is asking the CPU to do
- Execute — actually do it (add, compare, jump, etc.)
Then repeat. Fetch. Decode. Execute. Over and over, billions of times per second.
That's the loop behind every program you've ever run — your browser, your editor, this website. Same cycle, different instructions.
Day 1 of OS fundamentals. More tomorrow.