📚 IGCSE Computer Science: End-of-Term Revision Guide | IGCSE 计算机：期末复习提纲
This revision guide covers the core topics of the IGCSE Computer Science course. It is designed to help you consolidate key concepts before the end-of-term exam. Use it alongside past papers and practical programming exercises for the best results.
本复习提纲涵盖 IGCSE 计算机科学课程的核心主题，旨在帮助你在期末考前巩固关键概念。请搭配历年真题和实际编程练习使用，以获得最佳复习效果。
1. Data Representation | 数据表示
Computers store all data as binary digits (bits). Understanding number bases, encoding methods, and file size calculations is essential for the exam.
计算机将所有数据存储为二进制数字（比特）。理解进制转换、编码方法和文件大小计算对考试至关重要。
Binary, denary, and hexadecimal systems. Conversions between these number bases are frequently tested. Hex digits A–F represent 10–15.
二进制、十进制和十六进制。这些进制之间的相互转换经常出现在考题中。十六进制数字 A–F 分别代表 10–15。
Binary addition and overflow. When adding two 8‑bit numbers, a 9th bit may be produced, indicating an overflow error.
二进制加法和溢出。当两个 8 位数相加时，可能产生第 9 位，这标志着溢出错误。
Text representation: ASCII and Unicode. ASCII uses 7 or 8 bits per character, while Unicode uses up to 32 bits to cover global scripts.
文本表示：ASCII 和 Unicode。ASCII 每个字符用 7 或 8 位，Unicode 最多使用 32 位，以覆盖全球书写系统。
Image, sound, and compression. Bitmap images are grids of pixels; sound is sampled. Compression can be lossy (JPEG, MP3) or lossless (PNG, ZIP).
图像、声音和压缩。位图图像是像素网格；声音通过采样存储。压缩分为有损（JPEG、MP3）和无损（PNG、ZIP）两种。
ht × colour depth (bits). Sound file size = sample rate × bit depth × duration × channels.
文件大小计算：图像大小 = 宽 × 高 × 颜色深度（位）。声音文件大小 = 采样率 × 位深度 × 时长 × 声道数。
Example: an 8‑bit colour depth allows 2⁸ = 256 colours per pixel. A 10‑second stereo audio sampled at 44.1 kHz with 16‑bit depth needs 44 100 × 16 × 10 × 2 = 14 112 000 bits (≈1.68 MB).
示例：8 位颜色深度每个像素允许 2⁸ = 256 种颜色。一段 10 秒的立体声，采样率 44.1 kHz，位深度 16 位，所需大小为 44 100 × 16 × 10 × 2 = 14 112 000 位（约 1.68 MB）。
2. Communication and Internet Technologies | 通信与互联网技术
Networking concepts, the internet, and web technologies appear regularly. You should be able to describe protocols, IP addressing, and HTML.
网络概念、互联网和网页技术经常出现。你应该能够描述协议、IP 地址和 HTML。
Types of network: LAN, WAN, WLAN. A LAN spans a small area; a WAN connects LANs over large distances.
网络类型：局域网、广域网、无线局域网。局域网覆盖小范围；广域网将局域网跨远距离连接。
Network hardware: router, switch, hub, NIC, modem. Routers forward data packets between networks using IP addresses.
网络硬件：路由器、交换机、集线器、网卡、调制解调器。路由器根据 IP 地址在网间转发数据包。
The internet: a global WAN using TCP/IP. IP addresses can be IPv4 (32‑bit) or IPv6 (128‑bit). DNS translates domain names to IPs.
互联网：使用 TCP/IP 的全球广域网。IP 地址分为 IPv4（32 位）和 IPv6（128 位）。DNS 将域名翻译为 IP 地址。
Protocols: HTTP, HTTPS, FTP, SMTP, POP3, IMAP. HTTPS encrypts data with SSL/TLS for secure transfer.
协议：HTTP、HTTPS、FTP、SMTP、POP3、IMAP。HTTPS 使用 SSL/TLS 加密数据，实现安全传输。
HTML basics: tags such as
<h1>,<p>,<a href>,<img>. An HTML document must have<html>,<head>, and<body>sections.HTML 基础：标签如
<h1>、<p>、<a href>、<img>。HTML 文档必须包含<html>、<head>和<body>部分。
3. Computer Architecture | 计算机体系结构
The Von Neumann architecture is central to IGCSE Computer Science. You need to know the roles of CPU components and the fetch‑decode‑execute cycle.
冯·诺依曼体系是 IGCSE 计算机科学的核心。你需要掌握 CPU 各部件的角色和取指–译码–执行循环。
Central Processing Unit (CPU): consists of the Control Unit (CU), Arithmetic Logic Unit (ALU), registers, and buses.
中央处理器（CPU）包含控制单元（CU）、算术逻辑单元（ALU）、寄存器和总线。
Key registers: Program Counter (PC), Memory Address Register (MAR), Memory Data Register (MDR), Current Instruction Register (CIR), Accumulator (ACC).
关键寄存器：程序计数器（PC）、内存地址寄存器（MAR）、内存数据寄存器（MDR）、当前指令寄存器（CIR）、累加器（ACC）。
Fetch‑decode‑ PC → MAR → memory read to MDR, then to CIR, decoded by CU, executed by ALU, result stored.
取指–译码–执行循环：PC ⇒ MAR ⇒ 内存读取至 MDR，再送 CIR，CU 译码，ALU 执行，结果存储。
Factors affecting CPU performance: clock speed (GHz), number of cores, cache size.
影响 CPU 性能的因素：时钟频率（GHz）、核心数量、缓存大小。
Embedded systems: dedicated computers inside larger devices, e.g., washing machines, cars. They usually have a microcontroller and run a single program.
嵌入式系统：嵌入在大型设备中的专用计算机，如洗衣机、汽车。它们通常含有一个微控制器，只运行单一程序。
4. Input and Output Devices | 输入与输出设备
You must be able to describe the operation of common input and output devices and choose appropriate ones for a given scenario.
你必须能描述常见输入/输出设备的工作原理，并针对特定场景选择合适的设备。
Input devices: keyboard, mouse, microphone, touch screen, scanner, sensors (temperature, light, pressure, proximity).
输入设备：键盘、鼠标、麦克风、触摸屏、扫描仪、传感器（温度、光照、压力、接近）。
Output devices: monitor, projector, printer (laser, inkjet, 3D), speakers, actuators.
输出设备：显示器、投影仪、打印机（激光、喷墨、3D）、扬声器、执行器。
Touchscreen technologies: resistive (pressure-based), capacitive (uses electrical charge of skin), infra‑red.
触摸屏技术：电阻式（基于压力）、电容式（利用皮肤电荷）、红外式。
Printers: laser uses static electricity and toner, fast and high quality; inkjet sprays liquid ink, good for photos.
打印机：激光打印机利用静电和墨粉，速度快、质量高；喷墨打印机喷射液体墨水，适合照片打印。
Sensors convert a physical quantity into an analogue signal, which is then digitised by an ADC for the computer to process.
传感器将物理量转换为模拟信号，再由模数转换器（ADC）数字化，供计算机处理。
5. Memory and Storage | 内存与存储
Distinguish between primary and secondary storage, and between volatile and non‑volatile memory. Recent specifications also include cloud storage.
要区分主存与辅存，以及易失性与非易失性存储器。最新考纲还包括云存储。
RAM (Random Access Memory): volatile, stores data and programs currently in use. More RAM allows more multitasking.
RAM（随机存取存储器）：易失性，存储当前使用的数据和程序。更大的 RAM 允许更多任务并行。
ROM (Read Only Memory): non‑volatile, holds firmware/BIOS. Data cannot be changed easily.
ROM（只读存储器）：非易失性，存储固件/BIOS。数据难以更改。
Secondary storage: magnetic (HDD), optical (CD, DVD, Blu‑ray), solid state (SSD, USB flash drive). SSDs have no moving parts and are faster.
辅存：磁存储（HDD）、光存储（CD、DVD、蓝光）、固态存储（SSD、U盘）。SSD 无移动部件，速度更快。
Cloud storage: remote servers accessed via the internet. Advantages: accessibility, backup; disadvantages: need internet, security.
云存储：通过互联网访问的远程服务器。优点：可访问性、自动备份；缺点：需联网、安全问题。
6. Software | 软件
Software can be categorised as system software or application software. Know the functions of an operating system and how high‑level languages relate to machine code.
软件可分为系统软件和应用软件。要掌握操作系统的功能，以及高级语言与机器码的关系。
System software: operating system (OS), utility programs, compilers, linkers. The OS manages hardware, provides a user interface, and handles multitasking.
系统软件：操作系统、实用程序、编译器、链接器。操作系统管理硬件、提供用户接口并处理多任务。
Application software: word processors, spreadsheets, databases, web browsers. They perform specific user‑oriented tasks.
应用软件：文字处理、电子表格、数据库、浏览器。它们完成面向用户的具体任务。
High‑level language vs. machine code: HLL is human‑readable (Python, Java) and must be translated. Machine code is binary, directly executed by the CPU.
高级语言与机器码：高级语言（如 Python、Java）人类可读，须经翻译；机器码是二进制编码，可直接由 CPU 执行。
Translators: compiler (translates all code at once), interpreter (translates line‑by‑line), assembler (assembly language to machine code).
翻译程序：编译器（一次性翻译全部代码）、解释器（逐行翻译）、汇编器（将汇编语言转为机器码）。
7. Boolean Logic and Computer Ethics | 布尔逻辑与计算机伦理
Logic gates form the basis of digital circuits. Additionally, you will be expected to discuss ethical issues such as data privacy and the digital divide.
逻辑门是数字电路的基础。此外，你需要讨论数据隐私与数字鸿沟等伦理问题。
Basic logic gates: NOT, AND, OR, NAND, NOR, XOR. Truth tables show outputs for all input combinations.
基本逻辑门：非门、与门、或门、与非门、或非门、异或门。真值表列出所有输入组合下的输出。
Logic circuits: combine gates to produce more complex functions. A simple half‑adder uses an XOR and an AND gate to add two bits.
逻辑电路：组合逻辑门产生更复杂的功能。半加器利用异或门和与门实现两个比特相加。
Boolean expressions can be simplified using laws like A • A = A, A + (A • B) = A. Notation often uses
•for AND,+for OR, overbar for NOT.布尔表达式可用定律化简，如 A • A = A，A + (A • B) = A。表示法中
•代表与，+代表或，上划线代表非。
A XOR B = (A • B̄) + (Ā • B)
Computer ethics: plagiarism, hacking, malware creation, digital divide, online privacy. Laws like the Data Protection Act protect personal data.
计算机伦理：剽窃、黑客入侵、制造恶意软件、数字鸿沟、在线隐私。《数据保护法》等法律保护个人数据。
Free software vs. open source vs. proprietary: understand differences in licensing and cost. Free software emphasizes user freedom, not necessarily zero price.
自由软件 vs. 开源 vs. 专有软件：理解许可和费用的区别。自由软件强调用户自由，而不一定免费。
8. Programming Concepts | 编程概念
Programming theory underpins practical coding. You should be confident with data types, control structures, arrays, and the use of pseudocode.
编程理论是实践编码的基础。你应熟练掌握数据类型、控制结构、数组以及伪代码的使用。
Variables and constants: a variable’s value can change; a constant’s value is fixed during execution. Declare with meaningful identifiers.
变量与常量：变量的值可变；常量的值在运行期间固定。用有意义的标识符声明。
Data types: integer, real (float), char, string, Boolean. Operations only work correctly when data types match.
数据类型：整型、实型（浮点型）、字符、字符串、布尔型。只有当数据类型匹配时，运算才能正确执行。
Sequence, selection, iteration: Sequence runs in order; selection uses IF...THEN...ELSE...ENDIF; iteration uses FOR...NEXT, WHILE...ENDWHILE, REPEAT...UNTIL.
顺序、选择、循环：顺序按次序执行；选择使用 IF...THEN...ELSE...ENDIF；循环使用 FOR...NEXT、WHILE...ENDWHILE、REPEAT...UNTIL。
Arrays: one‑dimensional (list) and two‑dimensional (table). Index usually starts at 0 or 1. Used to store multiple values of the same type.
数组：一维（列表）和二维（表格）。索引通常从 0 或 1 开始。用于存储多个同类型值。
Pseudocode conventions: use INPUT, OUTPUT, ← for assignment, comparison operators =, <, >, <=, >=, <>. Example:
IF score > 60 THEN OUTPUT "Pass".伪代码规范：使用 INPUT、OUTPUT，赋值用 ←，比较运算符 =、<、>、<=、>=、<>。示例：
IF score > 60 THEN OUTPUT "Pass"。
9. Algorithms and Problem‑Solving | 算法与问题解决
Algorithm design and testing are examined through trace tables, flowchart interpretation, and standard searching/sorting algorithms.
算法设计与测试通过跟踪表、流程图解释以及标准搜索/排序算法来考查。
Flowchart symbols: oval for start/end, rectangle for process, diamond for decision, parallelogram for input/output. Arrows show direction.
流程图符号：椭圆形表示开始/结束，矩形表示处理，菱形表示判断，平行四边形表示输入/输出。箭头指示方向。
Linear search: checks each element in a list until the target is found. Works on unsorted lists; average performance O(n).
线性搜索：逐个检查列表元素直到找到目标。适用于无序列表；平均性能为 O(n)。
Bubble sort: repeatedly compares adjacent elements and swaps if needed. After each pass, the largest unsorted value bubbles to the end.
冒泡排序：反复比较相邻元素，必要时交换。每趟循环后，最大的未排序元素“冒泡”到末尾。
Test data: normal, boundary, and erroneous data should be used to verify an algorithm. Boundary tests check extreme values like 0, maximum, or empty input.
测试数据：应使用正常、边界和异常数据来验证算法。边界测试检查极值，如 0、最大值或空输入。
Trace tables: a systematic way to track variable values step‑by‑step during an algorithm run. Essential for identifying logic errors.
跟踪表：一种在算法运行时逐步记录变量值的系统方法，对于排查逻辑错误至关重要。
10. Security and Ethics | 安全与伦理
Protecting data and understanding the consequences of computer misuse are recurring themes. This unit often appears in scenario‑based questions.
保护数据并理解计算机滥用的后果是反复出现的主题，该单元常出现在情景式题目中。
Malware: virus, worm, Trojan horse, spyware, ransomware. A worm replicates without user action; ransomware encrypts files and demands payment.
恶意软件：病毒、蠕虫、特洛伊木马、间谍软件、勒索软件。蠕虫无需用户操作即可自我复制；勒索软件加密文件并勒索赎金。
Social engineering: phishing, pharming, pretexting. Phishing uses deceptive emails to steal credentials.
社会工程学：网络钓鱼、域欺骗、借口欺诈。网络钓鱼利用欺骗性邮件窃取凭证。
Security measures: firewall, anti‑virus, encryption, two‑factor authentication, strong passwords, biometrics. Encryption scrambles data so it can only be read with a key.
安全措施：防火墙、防病毒、加密、双因素认证、强密码、生物识别。加密打乱数据，只有用密钥才能读取。
Data integrity and backups: regular backups prevent data loss. Full and incremental backups differ in how much data is copied each time.
数据完整性与备份：定期备份可防止数据丢失。完全备份与增量备份的差异在于每次复制多少数据。
Legal and ethical issues: the Computer Misuse Act, Copyright Act, GDPR (or local data protection law). Unauthorised access, modification, and sharing are illegal.
法律与伦理问题：《计算机滥用法》、《版权法》、GDPR（或当地数据保护法）。未经授权的访问、篡改和分享均属违法。
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