🛡️Cyber Security
Foundations · Lesson 2/9

Computer Basics — How Machines Really Work

25 min 2 exercises 1 quiz

What you'll learn

  • What actually happens inside a computer (CPU, RAM, storage)
  • Why everything is 1s and 0s (binary) — and you'll convert some yourself
  • Hexadecimal — the shorthand security tools use for everything from hashes to file signatures
  • What an operating system does
  • The words every security professional uses daily

Security is about protecting computers, so first you must understand what a computer is.

The kitchen analogy 🍳

A computer is like a kitchen:

  • CPU (processor) = the chef. Does all the actual work, one step at a time — but incredibly fast (billions of steps per second).
  • RAM (memory) = the countertop. Fast workspace for what you're cooking right now. Turn off the power and it's wiped clean.
  • Storage (SSD/hard drive) = the fridge/pantry. Keeps things permanently, even when off — but slower to reach than the countertop.
  • Operating System (Windows, Linux, macOS) = the kitchen manager. Decides who uses the chef, how the countertop is shared, and who's allowed in.

Why binary? A computer is millions of tiny switches. A switch is either ON (1) or OFF (0). That's it. Every photo, song, and password is ultimately a huge pattern of ON/OFF switches. We group 8 switches into a byte, and a byte can represent one letter.

Counting in binary is just like normal counting, but with only two digits (0 and 1) instead of ten:

Decimal:  0  1  2  3  4  5  6  7  8
Binary:   0  1 10 11 100 101 110 111 1000

Each position is a power of 2: …, 8, 4, 2, 1. So 101 = 4 + 0 + 1 = 5.

Run this Python (the environment loads the first time — ~10 seconds). bin() shows the switches, int(x, 2) reads them back. Change the number and re-run.

# Python can convert between decimal and binary instantly
number = 5
print("5 in binary is:", bin(number))     # 0b101

# and back again
print("Binary 1010 is:", int("1010", 2))  # 10

# a byte holds 8 bits -> values 0 to 255
print("Max value of one byte:", 2**8 - 1) # 255
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Exercise 1

Write Python that:

  1. Stores your age in a variable age
  2. Prints its binary form using bin(age)
  3. Prints how many bytes it takes to store the number 300 as a variable bytes_needed — hint: one byte holds up to 255, so 300 needs 2.
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Hexadecimal — binary's shorthand 🔢

Binary is precise but painfully long — a single byte is 8 characters (11010110). Security tools almost never show you raw binary; they show hexadecimal (base 16) instead, because 2 hex digits pack exactly one byte:

Binary:  11010110  →  Hex:  D6

Hex uses 16 symbols: 0-9 then A-F (where A=10, B=11, … F=15). You'll recognize hex everywhere in security work:

  • MAC addresses: 3C:A6:F6:1E:2B:9D — each pair is one byte in hex
  • File signatures ("magic bytes"): every file type starts with a fixed hex pattern regardless of its extension — a JPEG always starts FF D8 FF, a PDF starts 25 50 44 46. Malware analysts rename suspicious files and check these bytes, because an attacker can label a program "photo.jpg" but can't hide its true magic bytes.
  • Hashes (like MD5, SHA-256) are always displayed as long hex strings.
  • Colors in web design (#FF5733) are hex too — same system, different use.

Python converts to hex just as easily as binary:

print(hex(214))          # '0xd6'
print(int("d6", 16))     # 214
Exercise 2

Write Python that:

  1. Converts the number 255 to hex and stores the string result in hex_value
  2. Converts the hex string "ff" back to a decimal number, stored in decimal_value

(Use hex(x) and int(x, 16) — the same pattern you used for binary.)

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Quick quiz

Question 1 of 6

Which part loses its contents when the power goes off?

Question 2 of 6

What is the decimal value of binary 110?

Question 3 of 6

How many bits are in one byte?

Question 4 of 6

What does the operating system do?

Question 5 of 6

Why do security tools display data in hex instead of raw binary?

Question 6 of 6

Why do malware analysts check a file's 'magic bytes' instead of trusting its file extension?

Summary

  • CPU = chef, RAM = countertop (volatile), Storage = pantry (permanent), OS = manager
  • Everything is binary: switches grouped into bytes (8 bits = 1 character)
  • Hexadecimal is binary's compact shorthand — used in MAC addresses, hashes, and file signatures
  • You converted numbers with Python's bin()/int(x, 2) and hex()/int(x, 16)

Next: Networking — how these computers talk to each other, and where attackers try to listen in.

Practice

Reading is not learning until you run something. Pick one.

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