# What a Server Actually Is

You've heard the word "server" a thousand times. The website is "down because the server crashed." Your
files are "on the server." Someone "spun up a server" to run the app. And somewhere along the way, the word
turned into a kind of fog - a mysterious, important machine in a faraway room that you're not supposed to
understand.

Here's the relief, up front: a server is not a special breed of computer. It's an ordinary computer running
an ordinary kind of program - one that sits there, waits for someone to ask it for something, and answers.
That's it. Once you see that clearly, the whole world of infrastructure - addresses, the cloud, renting
machines you'll never touch - stops being intimidating and starts being *reasonable*.

This is the "A" of infrastructure. Everything else you'll learn - connecting to servers, deploying to them,
renting them from a cloud provider - rests on this one idea.

## How to read this

- **Just want the one-sentence answer?** A server is a computer running a program that waits for requests and
  responds to them. Read [Phase 1](01-a-computer-thats-always-on.md) for why that's the whole story.
- **Want it to finally make sense?** Read in order. Each phase builds the picture: first what a server *is*,
  then what earns a computer the name "server," then how a server goes from a physical box to a rented sliver
  of the cloud.

## The phases

1. **[A Computer That's Always On](01-a-computer-thats-always-on.md)** - a server is just a computer running a
   program that waits for and answers requests. We demystify the word (your laptop can be a server) and meet
   the client/server model.
2. **[What Makes It a "Server"](02-what-makes-it-a-server.md)** - the traits that turn an ordinary computer
   into one we call a server: headless, always-on, reachable at an address, running server software, playing
   the request/response role.
3. **[From a Box to the Cloud](03-from-a-box-to-the-cloud.md)** - the ladder from a physical machine to a
   virtual machine to a cloud instance to serverless, and what "the cloud is someone else's computer" really
   means.

> This guide stops at *understanding* servers. Actually connecting to one and running commands on it is its
> own skill - see [SSH and Keys](/guides/ssh-and-keys). Choosing and renting one from a provider is covered in
> [Cloud Platforms Explained](/guides/cloud-platforms-explained).