How computers really work.
You can't protect something you don't understand. So today we open up the computer, not with a screwdriver, but with a biryani kitchen. By the end, words like CPU, RAM and "process" will feel easy.
Hackers don't attack "a computer". They attack a specific part of it: its memory, a running program, a stored file. Once you know the parts, you'll understand every attack in this course.
A computer is a restaurant kitchen
Imagine a busy biryani restaurant kitchen on a Friday night. Orders keep coming, cooks are working, food is going out. A computer (and your phone) works in exactly the same way.
| In the kitchen | In the computer | What it does |
|---|---|---|
| Head cook | CPU (processor) | Does the actual work, billions of tiny steps every second. |
| Kitchen counter | RAM (memory) | Holds whatever is being cooked right now. Fast, but small, and wiped clean when the shop closes (when you switch off). |
| Store room | Storage (SSD / phone storage) | Keeps everything for the long term: photos, apps, documents. Big, but slower to reach. |
| Manager | Operating system (Windows, Android, Linux) | Decides which order goes first, who may enter the store room, and keeps everyone working together. |
| Recipes | Apps and programs | Step-by-step instructions the cook follows. |
| Waiters | Input and output | Bring requests in (keyboard, touch, mic) and take results out (screen, speaker). |
So when you open WhatsApp: the recipe (the app) is taken from the store room (storage), placed on the counter (RAM), and the head cook (CPU) starts following it. The manager (Android) watches over all of it.
Your phone restarts and the half-written message you hadn't sent is gone, but your photos are still there. Why?
Exactly. Unsaved things live on the "counter" (RAM). Saved things live in the "store room" (storage). This matters in security too: some malware lives only in RAM, so investigators try to capture memory before switching a hacked computer off.
Everything is just 0s and 1s
Deep inside, a computer only understands two things: on and off. We write them as 1 and 0. One 0-or-1 is called a bit. Eight bits together make a byte, which is enough to store one letter, like "A".
- 1 KB (kilobyte) ≈ 1,000 bytes: a short WhatsApp message.
- 1 MB (megabyte) ≈ 1,000 KB: one good photo from your phone (2–4 MB).
- 1 GB (gigabyte) ≈ 1,000 MB: about a 1-hour HD movie.
- 1 TB (terabyte) ≈ 1,000 GB: a big laptop hard disk.
Photos, songs, videos, apps, even viruses: they are all just very long lists of 0s and 1s. A virus isn't magic. It's a program, just like a calculator app, but written to do something harmful.
Programs, processes and permissions
A program is a recipe sitting in the store room. When you open it, it becomes a process: a recipe that's actually being cooked right now. Right now your phone probably has 30 or more processes running, most of which you never see.
Now the important part for security. A good manager doesn't give every worker the key to the cash box. Computers work the same way:
- A normal user (standard account) can use apps and their own files.
- An administrator (on Linux called root) can change anything: install software, read everyone's files, switch off protection.
That's why attackers dream of getting admin or root access. If malware runs as a normal user, the damage is limited. If it runs as admin, it owns the whole kitchen. In security this jump is called privilege escalation, and you'll hear that phrase a lot.
When an app asks for permissions it doesn't need (a torch app wanting your contacts and SMS), that's a red flag. You are the manager. Say no.
Why updates matter so much
Recipes sometimes have mistakes. Maybe step 7 says "leave the back door open while cooking". Nobody notices, until a thief does. In software these mistakes are called bugs, and bugs that attackers can use are vulnerabilities (remember Lesson 1?).
When companies find these mistakes, they fix the recipe and send you the new version: that's an update or patch. Every day you delay an update, the back door stays open, and attackers often know about it, because the update itself tells the world what was fixed.
Malware gets onto a laptop where the person always uses an administrator account. Why is this worse than a normal account?
Right. A program runs with the power of the person who started it. That's why professionals use a normal account for daily work and only use admin when they really need it. It's called the principle of least privilege, a phrase interviewers love.
Your task for today (10 min)
Look inside your own kitchen. On a laptop: press Ctrl + Shift + Esc to open Task Manager and look at the "Processes" tab: find the process using the most memory. On Android: open Settings → Apps and scroll through every app. Delete any app you don't recognise or don't use, and check the permissions of two apps you do use. Finally, install any pending updates.
Which statement is TRUE?
Correct. 128 GB is storage, not RAM. A virus is just a program. And updates close known holes, so update quickly.
Lesson 2 complete!
You now know the parts of a computer, bits and bytes, processes, admin vs user, and why updates matter. Next we'll follow a message across the internet.
Next: The internet, explained with a courier →