1Data Representation

1.1 Number systems

Computers store all data as binary (base 2). Humans group binary into hexadecimal (base 16) because each hex digit maps to exactly 4 bits, making long binary strings readable.

Binary Prefixes

Binary prefixes use powers of 1024 (2¹⁰): kibi (KiB) = 1024, mebi (MiB) = 1024², gibi (GiB) = 1024³, tebi (TiB) = 1024⁴. Decimal prefixes use powers of 1000: kilo = 10³, mega = 10⁶, giga = 10⁹, tera = 10¹².

Hexadecimal Usage

• Memory dump — display raw memory contents compactly
• Program error codes — hex error codes in crash reports
• Unicode character tables — code points written in hex

Overflow

1.2 Binary Coded Decimal (BCD)

Each decimal digit (0-9) is encoded in 4 bits independently. The number 47 in BCD is 0100 0111, not 00101111. Used where decimal accuracy matters (calculators, currency).

1.3 Negative numbers — two's complement

The most significant bit becomes the sign bit with a negative place value. In 8-bit two's complement the range is −128 to +127.

1.4 Characters — ASCII and Unicode

1.5 Images and sound

Bitmap Image

Bitmap images store a colour value for every pixel.

Vector Graphic

Vector images store geometric coordinates, drawing commands, and object properties (colour/line width). Advantages: resize without pixelation, smaller file size. Disadvantages: poor compression, unsuitable for photos. For logos & line art only.

Digital Sound

Sound is captured by sampling amplitude at regular intervals.

1.6 Compression

2Communication & Networks

2.1 LAN & WAN

2.2 Network Models

Client-Server

Central server provides resources, clients send access requests. Advantages: centralised security & backup, uniform resource management. Examples: web server, print server, file server.

Peer-to-Peer (P2P)

All devices equal, data stored separately on each device. Disadvantages: no unified security/backup, virus spread easily, offline devices lose shared data.

Thin Client vs Thick Client

2.3 Transmission mode & direction

• Serial: one bit at a time over one wire. Reliable over long distances. (USB, Ethernet)
• Parallel: multiple bits simultaneously over multiple wires. Fast over short distances; suffers from skew over long ones.
• Simplex: one direction only (TV broadcast).
• Half-duplex: both directions, not simultaneously (walkie-talkie).
• Full-duplex: both directions simultaneously (phone call).

2.4 Network topologies

2.5 Cloud Computing

Pros: Access anywhere with internet, provider handles backup & maintenance. Cons: Inaccessible without network, data security relies on third party.

2.6 Transmission Media

2.7 LAN Hardware

2.8 Router

Core Functions: Connect different networks (LAN to WAN); Forward packets based on destination IP; Maintain routing table; Assign private IP addresses to internal devices.

2.9 Ethernet & CSMA/CD

Working Flow: Device listens to channel before sending → sends data only when idle → collision triggers a jam signal → devices wait a random time to resend.

2.10 Bit Streaming

• Real-time Streaming (Live): Capture & broadcast instantly, cannot pause/rewind.
• On-demand Streaming: Pre-stored media on server, support pause, fast-forward, rewatch.
• Buffer Function: Cache preloaded data to avoid stuttering under low broadband speed.

2.11 Internet vs WWW

2.12 IP Address

• IPv4: 4 groups of 0-255 digits split by dots (32 bits).
• IPv6: 8 groups of 4-hex digits, double colon :: replace consecutive zero groups (128 bits).
• Public IP: Unique globally, accessible over internet.
• Private IP: Only accessible within local LAN, need NAT to access internet. Reserved segments: 10.0.0.0, 172.16.0.0-172.31.0.0, 192.168.0.0.
• Static IP: Fixed address, used for web servers (no DNS update required).
• Dynamic IP: Reassigned each time device reconnects.

2.13 DNS (Domain Name Service)

Workflow: Browser sends domain request to DNS server → DNS matches the domain to its IP and caches the result → returns the IP to the browser.

2.14 Protocols

• HTTP / HTTPS: web pages. HTTPS adds TLS encryption.
• FTP: file transfer.
• SMTP / POP3 / IMAP: email send / receive.

3Computer Hardware

3.1 Primary vs Secondary Storage

3.2 RAM vs ROM

3.3 SRAM vs DRAM

3.4 ROM Types

3.5 Secondary & off-line storage

3.6 Embedded System

3.7 Peripheral Working Principles

3.8 Buffer

3.9 Logic Gates

3.10 Monitoring & Control Systems

Sensor Types: temperature, pressure, infrared, sound, light, accelerometer. Actuator: converts electrical signal to mechanical movement. Feedback Function: output result adjusts input value, keeps system within set range.

4Processor Fundamentals

4.1 Von Neumann Architecture

4.2 CPU Components

• ALU — Arithmetic Logic Unit. Performs arithmetic and bitwise operations.
• CU — Control Unit. Decodes instructions and orchestrates the other components.
• System Clock — unified timing signal for all operations.
• IAS — fast immediate access main memory.

Registers

4.3 System Buses

4.4 CPU Performance Factors

• Core Count: multi-core support parallel processing; limitation: software single-thread, memory bottleneck restrict speedup.
• Bus Width: wider bus = more bits transferred per clock cycle.
• Clock Speed: more instructions executed per second, limited by heat dissipation.
• Cache Size: larger cache stores more frequent data, reduce RAM access delay.

4.5 The fetch-execute cycle

1. Fetch: MAR ← PC; PC ← PC + 1; MDR ← [MAR]; CIR ← MDR.
2. Decode: CU interprets the opcode in CIR.
3. Execute: the operation is carried out; result may go to ACC or back to memory.

4.6 Interrupts

An interrupt is a signal that pauses normal CPU execution so a higher-priority task can be handled.

Handling: save state on stack — run ISR (interrupt service routine) — restore state — resume.

Sources: hardware fault, IO request, program runtime error, time slice end.

4.7 Assembly Language

Two-Pass Assembler

First Pass: scan code, build symbol table for labels & memory addresses. Second Pass: replace symbolic labels with absolute memory addresses, generate machine code.

Addressing Modes

Instruction Categories: data movement, IO, arithmetic, conditional/unconditional jump, comparison.

4.8 Bit Manipulation

Shift Operations

• Logical Shift: fill empty bits with 0.
• Arithmetic Right Shift: preserve sign bit for negative two's complement numbers.
• Cyclic Shift: bits overflow one end enter the other side.

Bitwise Operators

• AND: mask specific bits (judge odd/even, clear bits).
• OR: set target bits to 1.
• XOR: flip target bits.

5System Software

5.1 Operating-system functions

• Memory management: virtual memory, paging, memory isolation protection.
• File management: directory structure, file allocation, access permission control.
• Peripheral management: load device driver, handle buffer & interrupts.
• Process management: multitask scheduling, resource conflict resolution.
• Security management: user account, password, backup, access authority.
• User interface (GUI / CLI).

5.2 Utility programs

5.3 Program Library & DLL

Library: precompiled reusable functions, save development time, fully tested.

5.4 Translators

5.5 IDE Functions

6Security, Privacy & Data Integrity

6.1 Core Definitions

6.2 Common Security Defences

• Authentication: username + password, biometrics, digital signature.
• Firewall: filter inbound/outbound packets by pre-set rules.
• Anti-virus/Anti-spyware: scan & remove malicious software.
• Encryption: convert plaintext to ciphertext, unreadable without decryption key.

Digital Signature Flow

1. Hash file — message digest
2. Encrypt digest with sender's private key — signature
3. Receiver decrypts with sender's public key — expected digest
4. Receiver hashes message themselves and compares

6.3 Network Security Threats

6.4 Data Loss Prevention

Regular backup, disk mirroring (two identical storage disks), UPS uninterruptible power supply.

6.5 Data Validation vs Verification

7Ethics & Ownership

7.1 Computing Professional Ethical Code (BCS/IEEE)

Eight Principles: Prioritise public interest; Serve client & employer fairly; Ensure high-quality product; Independent objective judgment; Standardised team management; Fair to colleagues; Continuous self-learning & professional promotion.

7.2 Software Licence Types

• Copyright — automatic legal protection of original works; covers expression, not ideas.
• Patent — granted for novel inventions; lasts ~20 years; must be applied for.
• Free software (FSF definition) — the four freedoms: use, study, share, modify.

7.3 AI Applications & Impacts

Applications: face recognition, self-driving car, speech assistant, game AI, license plate recognition.

Social Impact: privacy risk from biometric data collection; reduce manual labour positions.

Economic Impact: cut labour cost for enterprises, extra expense on AI hardware & maintenance.

8Databases

8.1 Limitation of Flat File System

• Severe data redundancy & duplicate storage
• Data inconsistency (duplicated records update separately)
• Program-data dependency (modify data structure requires rewrite all related programs)
• Complex query hard to implement
• Difficult fine-grained access permission control

8.2 Relational Database Terminology

• Entity — a thing the database stores (Student, Book).
• Table — two-dimensional data set; Tuple = row (record); Attribute = column (field).
• Primary Key — uniquely identifies a row.
• Candidate Key — field qualified to be primary key.
• Foreign Key — match primary key of another table, build table relationship.
• Referential Integrity: foreign key must map existing primary key; support cascade update & cascade delete.
• Index: sorted pointer table, speed up search query.

8.3 Normalisation

8.4 DBMS Core Functions

• Data Dictionary: metadata storing table, field, data type, constraint & relationship.
• Three Schema Layers: External (user view), Conceptual (global model), Physical (disk storage structure).
• Database Security: user account, access permission, data encryption, operation log, scheduled backup.

8.5 SQL — DDL & DML basics

-- DDL
CREATE TABLE Student (
  StudentID INTEGER PRIMARY KEY,
  Name      VARCHAR(50) NOT NULL,
  ClassID   INTEGER,
  FOREIGN KEY (ClassID) REFERENCES Class(ClassID)
);
ALTER TABLE Student ADD Email VARCHAR(100);

-- DML Query
SELECT Name FROM Student WHERE ClassID = 1 ORDER BY Name;
SELECT ClassID, COUNT(*) AS NumStudents FROM Student GROUP BY ClassID;
SELECT S.Name, C.ClassName FROM Student S INNER JOIN Class C ON S.ClassID = C.ClassID;

-- DML Modify
INSERT INTO Student VALUES (42, 'Lin', 1);
UPDATE Student SET ClassID = 2 WHERE StudentID = 42;
DELETE FROM Student WHERE StudentID = 42;