Describe the main characteristics of AI

Computer Science – Cambridge IGCSE (0478) – Revision Notes

1. Data Representation

All data stored in a computer is ultimately a series of bits (0/1). The syllabus expects you to:

• Convert between binary, octal and hexadecimal (base‑2, base‑8, base‑16).
• Represent signed integers using two’s‑complement and explain overflow/underflow.
• Show the step‑by‑step conversion process in an exam.

Decimal	Binary (8‑bit)	Octal	Hexadecimal	Two’s‑Complement (signed)
0	0000 0000	00	00	0
13	0000 1101	015	0D	13
-13	1111 0011	373	F3	-13
255	1111 1111	377	FF	‑1 (if interpreted as signed – overflow)

Exam tip: Write the full two’s‑complement process – invert bits, add 1 – and state why adding 1 to the most‑positive value causes overflow.

2. Data Transmission & Security

2.1 Packet Structure

• Header – source address, destination address, length, checksum / CRC.
• Payload – the actual data being transferred.
• Trailer (optional) – end‑of‑packet marker.

2.2 Switching Methods

• Packet‑switching – data split into packets, each routed independently (used by the Internet).
• Circuit‑switching – a dedicated path is established for the whole communication (e.g., traditional telephone).

2.3 Common Interfaces

• USB – serial, hot‑plug, supports power delivery.
• Ethernet – CSMA/CD, uses MAC addresses.
• Wi‑Fi – wireless, uses SSID and encryption.

2.4 Error‑Detection Techniques

Technique	How it works	Simple example
Even parity	Add a single parity bit so total number of 1’s is even.	Data 1011 → parity 0 (four 1’s total).
Checksum	Sum all bytes, take modulo 256, send with packet.	Bytes 12 + 34 + 56 = 102 → checksum 102.
CRC (Cyclic Redundancy Check)	Polynomial division; remainder is appended.	Common in Ethernet frames.
ARQ (Automatic Repeat Request)	Receiver sends ACK/NACK; sender retransmits on NACK.	Stop‑and‑wait ARQ used in simple serial links.

2.5 Encryption Basics

• Symmetric key (e.g., AES) – same secret key encrypts and decrypts bulk data. Fast, but key must be shared securely.
• Asymmetric key (e.g., RSA) – public key encrypts, private key decrypts. Used for secure key exchange and digital signatures.

3. Computer Architecture (Hardware)

3.1 CPU Core Components

• ALU (Arithmetic‑Logic Unit) – performs calculations and logical operations.
• Control Unit – generates control signals for fetch‑decode‑execute.
• Registers – small, fast storage inside the CPU:
  • PC (Program Counter)
  • IR (Instruction Register)
  • MAR (Memory Address Register)
  • MDR (Memory Data Register)
  • ACC (Accumulator)
• Cache – L1, L2, L3 levels; stores recently used data/instructions.

3.2 Bus Types

Bus	Purpose	Typical width
Address bus	Specifies memory location to read/write	Usually 32 or 64 bits
Data bus	Transfers actual data	Same width as address bus
Control bus	Signals like read/write, interrupt, clock	Few lines (e.g., 8‑12)

3.3 Fetch‑Decode‑Execute Cycle

3.4 Instruction‑Set Design

• RISC (Reduced Instruction Set Computer) – many simple instructions, fixed length, often pipelined.
• CISC (Complex Instruction Set Computer) – fewer, more complex instructions, variable length.

3.5 Embedded Systems

Dedicated computers built into appliances. Example: a microwave’s controller reads keypad input, runs a simple program stored in ROM, and drives the magnetron via an actuator.

4. Software Fundamentals

4.1 System vs Application Software

• System software – operating system (OS) that manages hardware resources.
• Application software – programmes that perform user‑oriented tasks (e.g., word processor, web browser).

4.2 OS Functions

Function	What it does
Process management	Creates, schedules and terminates processes.
Memory management	Allocates RAM, handles paging/swapping.
File‑system management	Stores, retrieves, and protects files on storage media.
I/O control	Coordinates input and output devices via drivers.

4.3 Interrupts

An interrupt is a hardware signal that temporarily halts the CPU to service a high‑priority event.

• Example: Pressing a key generates a keyboard interrupt; the CPU saves the current state, runs the interrupt‑service routine to read the keycode, then resumes the original program.

4.4 Programming Language Levels

• Machine language – binary instructions directly executed by the CPU.
• Assembly language – mnemonic representation of machine instructions; requires an assembler.
• High‑level language – English‑like syntax (e.g., Python, Java); needs a compiler or interpreter.

4.5 Compilers vs Interpreters

Aspect	Compiler	Interpreter
When translation occurs	Before execution (produces an executable)	During execution (line‑by‑line)
Typical speed	Faster at run‑time	Slower, but easier to debug
Error reporting	All syntax errors found before program runs	Stops at first runtime error
Examples	GCC (C), javac (Java)	Python interpreter, PHP engine

4.6 Integrated Development Environments (IDEs)

• Syntax highlighting
• Code auto‑completion
• Built‑in debugger (breakpoints, step‑through)
• Project management & build tools

5. Internet & Its Uses

• Internet – global network of interconnected devices.
• World Wide Web (WWW) – collection of hyper‑linked documents accessed via HTTP/HTTPS.

5.1 URL Structure

protocol://domain[:port]/path?query#fragment

5.2 HTTP vs HTTPS

• Both use a request/response model (GET, POST, etc.).
• HTTPS adds TLS/SSL encryption, providing confidentiality and integrity.

5.3 Cookies & Sessions

• Cookies – small text files stored on the client; used for remembering preferences or login tokens.
• Sessions – server‑side data linked to a cookie‑based session ID; allows stateful interactions.

5.4 Digital Currency & Blockchain (Brief)

• Bitcoin uses a decentralized ledger where each block contains a hash of the previous block.
• Transactions are verified by a network of miners.

5.5 Cyber‑Security Threats & Mitigation

Threat	Typical impact	Mitigation
Malware	Unauthorised data access or system damage	Anti‑virus, regular updates
Phishing	Credential theft	User education, email filters
DDoS	Service unavailability	Firewalls, traffic‑scrubbing services
Man‑in‑the‑middle	Data interception/modification	HTTPS/TLS, VPNs

6. Data Management – SQL Basics

The Cambridge syllabus requires knowledge of the following commands:

• SELECT – columns to retrieve
• FROM – table name
• WHERE – filter rows
• ORDER BY – sort results
• SUM and COUNT – aggregate functions
• Logical operators AND, OR

Example query

SELECT product_name, SUM(quantity) AS total_sold
FROM sales
WHERE sale_date BETWEEN '2023‑01‑01' AND '2023‑12‑31'
GROUP BY product_name
ORDER BY total_sold DESC;

This returns each product with the total units sold in 2023, sorted from highest to lowest.

7. Boolean Logic & Logic Gates

Gate	Symbol	Truth Table (A B → Output)
NOT	¬A	0 → 1 1 → 0
AND	A ∧ B	00 → 0 01 → 0 10 → 0 11 → 1
OR	A ∨ B	00 → 0 01 → 1 10 → 1 11 → 1
NAND	¬(A ∧ B)	00 → 1 01 → 1 10 → 1 11 → 0
NOR	¬(A ∨ B)	00 → 1 01 → 0 10 → 0 11 → 0
XOR	A ⊕ B	00 → 0 01 → 1 10 → 1 11 → 0

Practice drawing the symbols and completing truth tables – they frequently appear in the logic‑design questions.

8. Algorithms, Programming & Logic

8.1 Flowchart Symbols (Cambridge standard)

• Oval – start / end
• Parallelogram – input / output
• Rectangle – process / assignment
• Diamond – decision (yes/no)
• Arrows – flow direction

8.2 Pseudocode Conventions

DECLARE i, sum AS INTEGER
SET sum ← 0
FOR i ← 1 TO 10 DO
    sum ← sum + i
END FOR
OUTPUT sum

8.3 Trace Tables

Use a table to record variable values after each step. Example for the loop above:

i	sum
1	1
2	3
…	…
10	55

8.4 Array Indexing Rules

• First element is at index 0 (most languages) or index 1 (some exam examples).
• Access outside the declared range causes a runtime error.

8.5 Test‑Data Categories

• Normal data – typical valid inputs.
• Boundary data – values at the limits of allowed ranges.
• Error data – illegal or unexpected inputs.

9. Automated & Emerging Technologies

9.1 Sensors, Actuators & Robotics

• Sensors – convert physical quantities (light, temperature, pressure) into electrical signals.
• Actuators – convert electrical signals into motion or force (motors, solenoids).
• Robotics cycle – perception → planning → control → actuation.

9.2 Artificial Intelligence (AI) – Main Characteristics

Characteristic	Description	Real‑World Example
Intelligence	Processes data to make informed decisions.	Product recommendation engines.
Learning	Improves performance from experience (machine learning).	Spam filter that adapts to new spam patterns.
Reasoning	Applies logical rules to infer new knowledge.	Expert system for medical diagnosis.
Perception	Interprets sensory input such as images or audio.	Image recognition in self‑driving cars.
Language Understanding	Comprehends and generates natural language.	Chatbot handling customer queries.
Problem‑Solving	Finds solutions to novel or complex tasks.	Robotic arm optimising assembly‑line sequencing.
Autonomy	Operates without continuous human control.	Unmanned aerial vehicle (drone) surveying farmland.
Adaptability	Adjusts behaviour when the environment or data changes.	Personalised learning platform that changes difficulty based on student performance.

9.3 Learning vs Reasoning

Learning extracts patterns from data (e.g., training a neural network on thousands of images).
Reasoning uses explicit logical rules (e.g., “if traffic light is red then stop”).
Most modern AI systems combine both: a self‑driving car learns to recognise pedestrians (learning) and then applies traffic‑law logic to decide when to brake (reasoning).

9.4 Typical AI System Architecture

10. Exam‑Ready Checklist

1. Convert numbers between decimal, binary, octal and hexadecimal; show two’s‑complement steps and explain overflow.
2. Draw and label a packet header; describe parity, checksum, CRC and ARQ with a short example.
3. Explain symmetric vs asymmetric encryption and illustrate a simple key‑exchange scenario.
4. Identify CPU registers (PC, MAR, MDR, ACC, IR) and describe the fetch‑decode‑execute cycle.
5. State the four main OS functions and give a concrete interrupt example (e.g., keyboard).
6. Contrast a compiler with an interpreter; list at least two IDE features.
7. Write a correct URL, differentiate HTTP from HTTPS, and explain the role of cookies.
8. List common cyber‑threats and two mitigation strategies for each.
9. Write a basic SQL query using SELECT, FROM, WHERE, ORDER BY, SUM, COUNT, AND, OR.
10. Draw symbols for NOT, AND, OR, NAND, NOR, XOR and complete a truth‑table exercise.
11. Produce a simple flowchart, write corresponding pseudocode, and construct a trace table.
12. Recall the eight AI characteristics, explain learning vs reasoning, and match each characteristic to a real‑world example.
13. Discuss why autonomy and adaptability are essential for drones, smart‑home devices and personalised education platforms.

Use the tables, diagrams and examples above for rapid revision – they condense the information most frequently tested in the Cambridge IGCSE Computer Science (0478) examinations.