Second Form Computing — RevisionHub

1

Back to the future: history of computing ✓

Pioneers, key inventions, encryption, public-key cryptography

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The pioneers

Alan Turing (1912–1954)

Broke Nazi Enigma codes in WW2. Father of computer science & AI.

Tim Berners-Lee (1955–)

Invented the World Wide Web (WWW) in 1989. Made it free for all.

George Boole (1815–1864)

Created Boolean logic (AND, OR, NOT) — the foundation of all computing.

Key inventions timeline

Year	Event
1840s	Charles Babbage designs the first mechanical computer concept
1854	George Boole invents Boolean logic
1940s	Alan Turing breaks the Enigma code; first electronic computers built
1989	Tim Berners-Lee invents the World Wide Web at CERN
1990s	Internet becomes public; personal computers in homes
2000s+	Smartphones, AI, cloud computing, social media

🌐

Internet vs Web The internet is the global network of computers. The World Wide Web is a service that runs on top of it — websites and links.

Why Alan Turing mattered

The Nazis used the Enigma machine to encrypt military messages
Turing built the Bombe machine to crack Enigma codes
Breaking the codes helped end WW2 years earlier, saving millions of lives
He also proposed the Turing Test — can a machine think like a human?

George Boole's lasting impact

Invented Boolean logic in 1854 — using TRUE/FALSE (1/0) for maths
Every computer chip in the world runs on Boolean logic
AND, OR, NOT gates (see Section 4) come directly from his work

Encryption — keeping data secure

Encryption = scrambling data so only the intended person can read it.

Plain text

"Hello Alice"

readable message

Encrypted

"Xq#7!pL2"

scrambled & secure

Decrypted

"Hello Alice"

readable again

Public key encryption

Key	What it does
Public key	Shared with everyone — used to lock (encrypt) the message
Private key	Kept secret by the owner — used to unlock (decrypt) the message
Why useful?	You can send secure messages without ever sharing a secret key — no risk of it being intercepted

🔐

Think of it like a padlock: anyone can click it shut (public key) but only you have the key to open it (private key).

✏️ Test yourself

Question 1

Who invented the World Wide Web, and in what year?

Explanation

Tim Berners-Lee invented the World Wide Web in 1989 while working at CERN.

Question 2

What did Alan Turing do in World War 2?

Explanation

Turing built the Bombe machine at Bletchley Park to crack Enigma codes. This helped end WW2 years earlier and saved millions of lives.

Question 3

What is the difference between the internet and the World Wide Web?

Explanation

The internet is the global network of computers. The World Wide Web is a service of websites and links that runs on top of it.

Question 4

What is encryption?

Explanation

Any data can be intercepted and read, but without the key it cannot be understood. Examples: HTTPS, WhatsApp messages, password storage.

Question 5

In public key encryption, which key is used to encrypt the message?

Explanation

The public key encrypts (locks) the message — anyone can use it. The private key decrypts (unlocks) — only the owner has it.

Question 6

Every modern computer chip is built from billions of what?

Explanation

Every processor is made of billions of tiny AND, OR, NOT logic gates — the system George Boole invented in 1854. That's why his work still matters today.

2

Programming ✓

Variables, selection, loops, common errors, game logic

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Core concepts — quick reference

Concept	Description
`Variable`	Named store for a value, e.g. `score = 0`, `lives = 3`
`if / elif / else`	Selection — runs different code depending on a condition
`while` loop	Repeats as long as a condition is true
`for` loop	Repeats a set number of times
`def` / function	Named block of reusable code
`print()`	Outputs text to the screen
`input()`	Asks the user to type something
`int()`	Converts a string to a whole number

Reading code — worked examples

What does this print?

score = 7
if score > 5:
    print("Win")
else:
    print("Lose")

score (7) is > 5, so the if branch runs → prints "Win"

What is the value of count?

count = 0
for i in range(3):
    count = count + 5
print(count)

Loop runs 3 times, adding 5 each time: 0 → 5 → 10 → 15

Common errors to spot

✗ Missing indent

Code inside if/loop must be indented — Python uses spacing as part of its rules

✓ Indent correctly

Use 4 spaces or a tab for code inside an if, for, or while

✗ Missing colon

if score > 5 — missing the colon at the end

✓ Add colon

if score > 5: — the colon after if/for/def/while is required

✗ Wrong operator

if score = 10: — single = assigns, doesn't compare

✓ Use ==

if score == 10: — double == compares values

✗ String vs int

age = input("Age: ") then doing maths — input is a string

✓ Convert to int

age = int(input("Age: "))

Game logic — lives & score system

A simple game in Python:

lives = 3
score = 0

while lives > 0:
    event = input("obstacle/coin? ")
    if event == "obstacle":
        lives = lives - 1
    elif event == "coin":
        score = score + 1

print("Game Over")

while lives > 0 — keeps the game running until lives run out
Each if/elif handles a different event
The loop exits automatically when lives reach 0

🎮

Good game design rules Hitting an obstacle → lose a life · Collecting a coin → gain a point · Lives reach 0 → display "Game Over" · Always define start state: lives = 3, score = 0

✏️ Test yourself

Question 1

score = 4. The code checks if score > 5 with an else branch. What prints?

Explanation

4 is not greater than 5, so the if condition is false. The else branch runs and prints "Lose".

Question 2

A loop runs for i in range(3) and adds 5 each time, starting from count = 0. What is the final value of count?

Explanation

The loop runs 3 times. Each time count grows by 5: 0 → 5 → 10 → 15.

Question 3

What is the difference between a while loop and a for loop?

Explanation

While loops repeat until a condition is false. For loops repeat a known number of times, usually using range().

Question 4

A player starts with 3 lives and 0 score. They hit 2 obstacles and collect 3 coins. What are lives and score?

Explanation

3 lives − 2 obstacles = 1 life. 0 score + 3 coins = 3 score.

Question 5

What is wrong with: if score = 10:?

Explanation

A single = is assignment. To compare values you need ==. Correct: if score == 10:.

Question 6

To stop a while loop in a game, what must happen?

Explanation

A while loop keeps running as long as its condition is true. When the condition becomes false (e.g. lives = 0), the loop exits.

3

AI: friend or foe? ✓

How AI learns, LLMs, bias, benefits and risks

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🤖

What is AI? A system that can make decisions or predictions based on data, without being explicitly programmed for every situation.

How AI learns — training

Training data

Thousands of examples fed in

AI model

Learns patterns by trial & error

Prediction

Makes decisions on new data

How AI learns — trial and error (reinforcement)

The reinforcement learning loop:

Take an action

Get reward / penalty

Update its model

repeats millions of times

Key AI concepts

📚

Large Language Models (LLMs) Trained on vast amounts of text. They work by predicting the most likely next word. They do NOT search the internet live or store books word for word.

⚖️

Bias in AI If training data is unbalanced (e.g. only male faces), the AI performs poorly on underrepresented groups. Garbage in = garbage out.

⚠️

Poor training data If an AI gives incorrect or unfair results, the most likely cause is poor, limited, or unrepresentative training data — not a hardware fault.

AI benefits and risks

Benefits	Risks
Diagnoses diseases from scans faster than humans	Biased decisions if training data is unrepresentative
Powers search engines, auto-correct, voice assistants	Deepfakes and misinformation spread more easily
Automates dangerous or repetitive tasks	Jobs displaced; privacy concerns with mass data use

Key terms

Term	Definition
AI	System that makes decisions or predictions — simulates human-like thinking
Training data	The examples the AI learns from — quality matters enormously
Bias	Unfair or inaccurate results caused by unrepresentative training data
LLM	Large Language Model — predicts likely next words to generate text (e.g. ChatGPT)
Algorithm	A set of step-by-step instructions a computer follows to solve a problem

✏️ Test yourself

Question 1

An AI trained to recognise handwriting only on typed fonts performs badly on cursive. What is the problem?

Explanation

The AI never saw cursive in training, so it can't recognise it. Garbage in = garbage out — unrepresentative training data leads to poor results.

Question 2

Which of these statements about a Large Language Model is FALSE?

Explanation

LLMs do NOT store books word-for-word. They learn patterns from training text and generate new text by predicting likely next words.

Question 3

Which of these is an example of AI being used in everyday life?

Explanation

Voice assistants, auto-correct, Netflix recommendations, spam filters, face unlock and satnav routing are all everyday examples of AI.

Question 4

What is bias in AI and what causes it?

Explanation

Bias means the AI gives unfair or wrong results for certain groups, caused by training data that didn't include enough varied examples.

Question 5

What is an algorithm?

Explanation

An algorithm is a set of clear step-by-step instructions a computer follows. AI uses algorithms to make decisions from training data.

Question 6

Which of these is a real risk of using AI in healthcare?

Explanation

If training data is mostly one ethnicity or sex, the AI may misdiagnose patients from underrepresented groups — a serious real-world risk.

4

Logic gates ✓

AND, OR, NOT — truth tables and real-world uses

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The three main gates

AND

Output is 1 only if BOTH inputs are 1

OR

Output is 1 if AT LEAST ONE input is 1

NOT

Flips the input: 0 → 1 and 1 → 0

Truth tables

AND gate

A	B	Output
0	0	0
0	1	0
1	0	0
1	1	1

OR gate

A	B	Output
0	0	0
0	1	1
1	0	1
1	1	1

NOT gate

Input	Output
0	1
1	0

Real-world examples

Gate	Real-world example
AND — security door	Opens ONLY if both keycard AND PIN are correct. Both must be 1.
OR — alarm system	Triggers if the door OR the window sensor detects movement. Either can be 1.
NOT — toggle switch	If light is ON (1), NOT flips it to OFF (0). Pressing again flips back.

🔗

George Boole connection Boolean logic (AND, OR, NOT) was invented by George Boole in 1854 — long before computers existed. Every processor in the world is built from billions of these logic gates.

✏️ Test yourself

Question 1

AND gate: A = 1, B = 0. What is the output?

Explanation

AND only outputs 1 when BOTH inputs are 1. Here B is 0, so the output is 0.

Question 2

OR gate: A = 0, B = 0. What is the output?

Explanation

OR outputs 1 when at least one input is 1. Both inputs are 0, so the output is 0.

Question 3

NOT gate: input = 0. What is the output?

Explanation

NOT flips the input. 0 becomes 1.

Question 4

A school fire alarm rings if the smoke sensor is triggered OR the manual button is pressed. Which gate models this?

Explanation

The alarm triggers if either the smoke sensor OR the button is activated. Only one needs to be true, so this is an OR gate.

Question 5

An alarm triggers if sensor A OR sensor B detects motion. A = 0, B = 1. Does the alarm trigger?

Explanation

OR triggers when at least one input is 1. B = 1 is enough, so the alarm triggers.

Question 6

A microwave only beeps when the door is NOT closed. Which gate is being used to flip the door's "closed" status?

Explanation

The NOT gate flips the input. "Door closed = 1" becomes "Not closed = 0", and vice versa, which the beep system uses to know when to alarm.

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Kitroniks: programming robots ✓

Movement, shapes, sensors and obstacle avoidance

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Robot movement — key commands

Command	Effect
`forward`	Move straight ahead — set speed and time/distance
`turn_left` / `turn_right`	Rotate the robot — angle determines turn amount
`stop`	Halt all motors immediately
`distance sensor`	Measures distance to nearest object — triggers actions when too close
`if distance <= 10`	When object is ≤10 cm away → typically stop or turn

Shapes from movement — the angle rule

📐

Exterior angle = 360 ÷ number of sides So a triangle (3 sides) needs 120° turns, a square (4 sides) needs 90° turns, a hexagon (6 sides) needs 60° turns.

Triangle

3 sides · turn 120° each

Square

4 sides · turn 90° each

L-shape

forward, turn 90°, forward again

Reading robot code — obstacle avoidance

What does this robot do?

while True:
    dist = sensor.read()
    if dist <= 10:
        robot.stop()
    else:
        robot.forward(50)

Reads sensor every loop cycle
If something is within 10cm → stop
Otherwise → move forward at speed 50

Tracing robot paths — triangle

for i in range(3):
    robot.forward(30)
    robot.turn_right(120)

Step	Action	Facing after
i = 0	Forward 30, turn 120°	120° (SE)
i = 1	Forward 30, turn 120°	240° (SW)
i = 2	Forward 30, turn 120°	Back to 0°

Result: a triangle — 3 × 120° = 360° total rotation.

Common patterns

Pattern	How
Straight line	`forward()` with no turns
Square	Repeat 4 times: forward + turn 90°
Triangle	Repeat 3 times: forward + turn 120°
L-shape	Forward, turn 90°, forward (different lengths)
Obstacle stop	`if distance <= threshold → stop()`

✏️ Test yourself

Question 1

A robot moves forward then turns 120°, three times. What shape does it draw?

Explanation

3 × 120° = 360° total rotation, returning to the start direction. With 3 sides this draws a triangle.

Question 2

To draw a regular hexagon (6 sides), what angle must the robot turn each time?

Explanation

Exterior angle = 360 ÷ number of sides = 360 ÷ 6 = 60°.

Question 3

What angle does the robot need to turn to draw a square?

Explanation

Exterior angle = 360 ÷ number of sides = 360 ÷ 4 = 90°.

Question 4

Code repeats 4 times: forward 20, turn right 90°. What shape and total distance?

Explanation

4 forward moves + 4 turns of 90° = a square. Distance: 4 × 20 = 80 units.

Question 5

The sensor reads 15 and the threshold is if dist <= 10. Does the robot stop or move?

Explanation

15 ≤ 10 is false, so the if branch is skipped and the else branch runs (move forward).

Question 6

How would you modify the triangle code to draw a square instead?

Explanation

A square has 4 sides — so range(4) — and exterior angle 360 ÷ 4 = 90° — so turn_right(90).

✨

Reinforce what you've learned

Optional · Listen, watch, and review the slides

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🎯

These are for reinforcement Listen to the podcast on the way to school. Watch the video before bed. Look over the slides any time. No notes needed — just notice how much you recognise now.

🎧 Podcast — How Boolean Logic Created Modern AI

A short audio explainer linking Boole's 1854 ideas to today's AI.

🎬 Video — The Idea That Built the World

A short film tying the year's content together.

📑 Slides — The System Blueprint

Slide deck reviewing the key concepts. Opens full screen with a back button.