2. Servers, storage and databases

A server is a computer that waits to serve other computers. That is it — the word 'server' just means a computer whose job is to respond to requests.

Imagine a coffee house in Addis Ababa. A customer (your phone or laptop) walks in and asks for coffee. The barista (the server) receives the order, prepares it, and hands it back. Your device makes a request; the server does the work and sends back the result.

A server can run on a tiny machine or on a giant rack of powerful hardware. What makes it a 'server' is not its size — it is its role: it listens for requests and responds to them. When you open TeleBirr and check your balance, a server somewhere received that request, looked up your account, and sent back the number you see on screen.

For many years, if a company wanted a server, they had to buy a physical machine, put it in an office, and pay staff to keep it running. A small business in the Merkato could not afford that — buying hardware, cooling it, and fixing it when it broke was expensive.

Cloud computing changed this. Today you can rent a server — called a Virtual Private Server (VPS) or a cloud instance — for as little as a few hundred birr a month. You do not touch the hardware. The cloud provider keeps the machines running in their data centre, and you access your server over the internet.

The server still does the same job as before (respond to requests), but now anyone — a student in Gondar, a startup in Hawassa, or a developer in Addis — can afford one. You pay only for what you use, just like paying for electricity rather than owning a power station.

Storage is where files live. A file can be anything: a photo you upload, a video a teacher records, a PDF certificate, a log from an app, or a backup of a database.

There are two main kinds of cloud storage:

1. Block storage — behaves like a traditional hard drive attached to your server. Your server reads and writes data directly. It is fast and suited for the server's own files, like the operating system and the app's code.

2. Object storage — designed for holding large amounts of files that many people or apps access. You upload a file, get a web link, and anyone with that link can download it. Think of platforms like Google Drive or Dropbox, but owned by the cloud provider. Object storage is cheap, scales to billions of files, and does not need a server to be running.

For example: an instructor at Ethio Telecom Learn records a course video (about 500 MB). That video is kept in object storage. When a learner in Dire Dawa presses play, their phone downloads the file directly from object storage — the server itself never has to send that big file every time.

A database is an organised collection of information that can be searched, sorted, and updated very quickly. Think of the difference between a disorganised pile of receipts in a drawer versus a well-kept ledger book — the ledger lets you find any transaction in seconds. A database is that ledger, but electronic and much faster.

Databases power almost everything:

• When Sara logs in to her TeleBirr account, a database looks up her username and password.

• When Abebe checks his balance, a database finds his account record and returns the number.

• When Almaz searches for a course on a learning platform, a database returns matching course titles instantly.

The most common type is a relational database (SQL). It stores data in tables — rows and columns, like a spreadsheet — and lets you link tables together. For example, a 'users' table and a 'transactions' table can be joined to show every payment a specific user made.

For apps that need more flexibility, there are NoSQL databases that store data as documents or key-value pairs, which is faster to set up for some use cases.

Servers, storage, and databases always work together. Here is what happens when Abebe opens a learning app on his phone and plays a video lesson:

1. His phone sends a request over the internet to the app's server.

2. The server asks the database: 'Is Abebe logged in? What lesson was he watching?' The database answers in milliseconds.

3. The server tells the phone: 'Here is the link to the video file in object storage.'

4. Abebe's phone fetches the video directly from object storage and plays it.

5. When Abebe completes the lesson, his phone tells the server, which writes a new record to the database: 'Abebe finished lesson 2.'

Remove any one of the three and the app breaks. No server — nobody to handle requests. No storage — no video to play. No database — no way to track progress or keep accounts.