IGCSE AQA Computer Science: End-of-Term Revision Guide | IGCSE AQA 计算机科学：期末复习提纲

📚 IGCSE AQA Computer Science: End-of-Term Revision Guide | IGCSE AQA 计算机科学：期末复习提纲

This comprehensive revision guide covers the key topics for the AQA IGCSE Computer Science syllabus. It is designed to help you consolidate your understanding before the end-of-term exam, with each core area broken down into clear English and Chinese explanations. Use this guide to strengthen both your technical vocabulary and conceptual clarity.

这份全面的复习提纲涵盖了 AQA IGCSE 计算机科学大纲的关键主题，旨在帮助你在期末考前巩固理解，每个核心领域都配有清晰的中英文解释。请使用本指南来加强你的技术词汇和概念清晰度。

1. Data Representation | 数据表示

Computers use binary (base‑2) to represent all data. The smallest unit is a bit, and 8 bits make a byte. Larger units include kibibytes (2¹⁰ bytes), mebibytes, and gibibytes.

计算机使用二进制（基数为 2）表示所有数据。最小单位是比特（bit），8 比特组成 1 字节（byte）。更大的单位有千字节（KiB, 2¹⁰ 字节）、兆字节（MiB）、吉字节（GiB）等。

Denary (base‑10) numbers can be converted to binary by successive division by 2, reading remainders from bottom to top. Hexadecimal (base‑16) uses digits 0‑9 and letters A‑F, often written with a 0x prefix or h suffix. One hex digit represents exactly 4 bits, making conversion between binary and hex very efficient.

十进制数可通过连续除以 2，从下往上读取余数转换为二进制。十六进制（基数为 16）使用数字 0‑9 和字母 A‑F，常写作 0x 前缀或 h 后缀。一个十六进制位恰好代表 4 个比特，因此在二进制和十六进制之间转换非常高效。

Binary addition follows simple rules: 0+0=0, 0+1=1, 1+0=1, 1+1=0 carry 1. Overflow occurs when the result requires more bits than available, often flagged by a carry out of the most significant bit.

二进制加法遵循简单规则：0+0=0, 0+1=1, 1+0=1, 1+1=0 并进位 1。当结果需要的位数超出可用位数时会产生溢出，通常通过最高位的进位来标记。

Characters are represented using standardised codes. ASCII uses 7 bits for 128 characters; extended ASCII uses 8 bits for 256 characters. Unicode (e.g. UTF‑8) allows representation of vastly more characters for global scripts.

字符使用标准化编码表示。ASCII 用 7 位表示 128 个字符；扩展 ASCII 用 8 位表示 256 个字符。Unicode（如 UTF‑8）可表示全球各种文字的大量字符。

Images are stored as a grid of pixels. In a bitmap, each pixel is represented by a binary code for its colour. Colour depth (bits per pixel) determines the number of available colours. Resolution (width × height) and colour depth together affect file size. Sound is sampled at regular intervals; sampling rate (Hz) and bit depth influence quality and file size.

图像以像素网格存储。在位图中，每个像素由其颜色的二进制编码表示。颜色深度（每个像素的位数）决定了可用颜色的数量。分辨率（宽×高）和颜色深度共同影响文件大小。声音按固定间隔采样；采样率（Hz）和位深度影响质量和文件大小。

Compression can be lossless (all original data can be restored, e.g. run‑length encoding, Huffman coding) or lossy (some data permanently removed to reduce size, e.g. JPEG, MP3). Lossless is essential for text and programs; lossy is acceptable for photos and audio where perceptual quality is maintained.

压缩分为无损压缩（可完全恢复原始数据，例如游程编码、哈夫曼编码）和有损压缩（永久删除部分数据以减小体积，例如 JPEG、MP3）。无损对于文本和程序至关重要；有损在感知质量得以保持的照片和音频中是可接受的。

2. Computer Systems | 计算机系统

The Central Processing Unit (CPU) fetches, decodes, and executes instructions. Its main components are the Control Unit (CU), Arithmetic Logic Unit (ALU), and registers such as the Program Counter, Accumulator, and Memory Address/Data Registers. The fetch‑decode‑execute cycle runs continuously.

中央处理器（CPU）取指、译码并执行指令。其主要部件包括控制单元（CU）、算术逻辑单元（ALU）以及程序计数器、累加器、存储器地址/数据寄存器等寄存器。取指‑译码‑执行周期持续运行。

CPU performance is affected by clock speed (cycles per second, measured in GHz), number of cores, and cache size. A high clock speed executes more instructions per second; multiple cores allow true simultaneous processing; cache stores frequently used data close to the CPU to reduce latency.

CPU 性能受时钟速度（每秒周期数，以 GHz 为单位）、核心数量和缓存大小的影响。高时钟速度每秒可执行更多指令；多核心可实现真正的并行处理；缓存将常用数据存储在 CPU 附近以减少延迟。

Embedded systems are specialised computers built into larger devices, usually running a dedicated function with minimal resources. Examples: washing machine controllers, car engine management, digital watches.

嵌入式系统是内置于大型设备中的专用计算机，通常以最少资源运行专门功能。例子：洗衣机控制器、汽车引擎管理、电子手表。

Primary memory includes RAM (volatile, stores data and instructions currently in use) and ROM (non‑volatile, stores firmware/boot instructions). Secondary storage devices such as magnetic hard disks, solid‑state drives (SSD), and optical discs are used for long‑term data retention. The key characteristics are capacity, speed, portability, durability, and cost.

主存包括 RAM（易失性，存储当前使用的数据和指令）和 ROM（非易失性，存储固件/引导指令）。辅助存储设备如磁性硬盘、固态硬盘（SSD）和光盘用于长期保留数据。关键特性是容量、速度、便携性、耐用性和成本。

3. Networks | 网络

A network is two or more computers connected to share resources. LANs (Local Area Networks) cover a small geographical area, while WANs (Wide Area Networks) connect LANs over large distances, often using public infrastructure.

网络是由两台或多台计算机连接起来以共享资源。LAN（局域网）覆盖较小地理区域，而 WAN（广域网）通过长距离连接多个 LAN，通常使用公共基础设施。

Common topologies include star (all devices connected to a central switch), bus (single backbone cable), and mesh (each device connected to several others). Star is the most common in modern Ethernet networks because it is easy to troubleshoot and scalable.

常见拓扑结构包括星型（所有设备连接到中央交换机）、总线型（单一主干电缆）和网状（每个设备与多个其他设备连接）。星型因其易于故障排除且可扩展，在现代以太网中最常见。

Protocols are sets of rules for communication. The TCP/IP stack has four layers: Application (HTTP, FTP, SMTP), Transport (TCP/UDP), Internet (IP), and Link (Ethernet/Wi‑Fi). Each layer adds its own header or trailer to the data.

协议是通信规则集合。TCP/IP 协议栈有四层：应用层（HTTP、FTP、SMTP）、传输层（TCP/UDP）、网络层（IP）和链路层（以太网/Wi‑Fi）。每一层为数据添加自己的头部或尾部。

IP addresses (IPv4: 32 bits, expressed as 4 octets; IPv6: 128 bits, hexadecimal) identify devices on a network. MAC addresses are 48‑bit physical addresses burned into network interface cards. Domain Name System (DNS) translates human‑readable domain names into IP addresses.

IP 地址（IPv4：32 位，表示为 4 个八位组；IPv6：128 位，十六进制）标识网络上的设备。MAC 地址是烧录在网卡上的 48 位物理地址。域名系统（DNS）将人类可读的域名转换为 IP 地址。

4. Network Security | 网络安全

Common threats include malware (viruses, worms, trojans, ransomware), phishing (fraudulent emails to steal credentials), brute‑force attacks, Denial of Service (DoS), and SQL injection. A ‘man‑in‑the‑middle’ attack intercepts communication between two parties without their knowledge.

常见威胁包括恶意软件（病毒、蠕虫、木马、勒索软件）、网络钓鱼（欺诈性电子邮件以窃取凭证）、暴力攻击、拒绝服务（DoS）和 SQL 注入。“中间人”攻击在双方不知情的情况下拦截通信。

Prevention methods: firewalls filter incoming/outgoing traffic according to rules; encryption (e.g. AES, RSA) makes data unreadable without a key; penetration testing identifies vulnerabilities; two‑factor authentication requires a second proof of identity. Regular software updates patch known security holes.

防护方法：防火墙根据规则过滤进出流量；加密（例如 AES、RSA）使数据在无密钥时不可读；渗透测试找出漏洞；双因素认证要求第二种身份证明。定期软件更新修补已知安全漏洞。

Physical security measures (locks, surveillance) and user access controls (passwords, biometrics) are equally important. Password policies should enforce complexity and periodic changes. A robust backup strategy (full, incremental) protects against data loss from ransomware or hardware failure.

物理安全措施（锁、监控）和用户访问控制（密码、生物特征）同样重要。密码策略应强制要求复杂性和定期变更。稳健的备份策略（完整备份、增量备份）可防止勒索软件或硬件故障导致的数据丢失。

5. Databases | 数据库

A database is a structured collection of data. In a relational database, data is stored in tables (relations). Each table has rows (records) and columns (fields). A primary key uniquely identifies each record; a foreign key links to a primary key in another table.

数据库是有结构的数据集合。在关系数据库中，数据存储在表（关系）中。每个表有行（记录）和列（字段）。主键唯一标识每条记录；外键链接到另一表的主键。

Data types include INTEGER, REAL/FLOAT, VARCHAR/STRING, DATE, BOOLEAN. Selecting appropriate data types helps maintain data integrity and saves storage space.

数据类型包括 INTEGER、REAL/FLOAT、VARCHAR/STRING、DATE、BOOLEAN。选择合适的数据类型有助于保持数据完整性并节省存储空间。

SQL (Structured Query Language) is used to query and manipulate relational databases. Common commands:

SQL（结构化查询语言）用于查询和操作关系数据库。常见命令：

SELECT * FROM Students WHERE Grade > 80; – Retrieve all columns for students with grade above 80.
SELECT * FROM Students WHERE Grade > 80; – 检索成绩大于 80 的学生所有列。
INSERT INTO Students (Name, Grade) VALUES (‘Ali’, 92); – Add a new record.
INSERT INTO Students (Name, Grade) VALUES (‘Ali’, 92); – 添加新记录。
UPDATE Students SET Grade = 95 WHERE Name = ‘Ali’; – Modify data.
UPDATE Students SET Grade = 95 WHERE Name = ‘Ali’; – 修改数据。
DELETE FROM Students WHERE Name = ‘Ali’; – Remove a record.
DELETE FROM Students WHERE Name = ‘Ali’; – 删除记录。

Normalisation reduces data redundancy by organising fields into multiple related tables, usually following 1NF (atomic values), 2NF (no partial dependencies), and 3NF (no transitive dependencies).

规范化通过将字段组织到多个相关表中来减少数据冗余，通常遵循 1NF（原子值）、2NF（无部分依赖）和 3NF（无传递依赖）。

6. Programming Concepts | 编程概念

Variables are named storage locations whose values can change; constants have fixed values. Variables and constants have associated data types: integer, real/float, Boolean, character, string. Type casting may be needed when converting between types.

变量是可以改变值的命名存储位置；常量具有固定值。变量和常量有对应的数据类型：整型、实型/浮点型、布尔型、字符、字符串。在类型之间转换时可能需要类型转换。

Programs use sequence, selection (if‑else, switch/case), and iteration (for, while, do‑while) to control flow. Nested structures allow complex logic.

程序使用顺序、选择（if‑else、switch/case）和迭代（for、while、do‑while）来控制流程。嵌套结构可实现复杂逻辑。

Subroutines (procedures and functions) modularise code. A procedure performs a task; a function returns a value. Parameters can be passed by value (a copy is used) or by reference (the original variable can be changed). Local variables exist only within the subroutine, while global variables are accessible throughout the program.

子程序（过程和函数）实现代码模块化。过程执行一个任务；函数返回一个值。参数可以通过按值传递（使用副本）或按引用传递（可以更改原变量）进行传递。局部变量只存在于子程序内部，而全局变量可在程序任何地方访问。

Common operators include arithmetic (+, -, *, /, MOD, DIV), comparison (==, !=, <, >, <=, >=), and logical (AND, OR, NOT). Understanding operator precedence prevents logic errors.

常用运算符包括算术（+、-、*、/、MOD、DIV）、比较（==、!=、<、>、<=、>=）和逻辑（AND、OR、NOT）。理解运算符优先级可防止逻辑错误。

Arrays (lists) hold multiple items of the same data type, accessed by index (usually starting at 0). Two‑dimensional arrays model tables. Records (structs) group fields of different types under one name.

数组（列表）存储多个同类型的数据项，通过索引（通常从 0 开始）访问。二维数组模拟表格。记录（结构）将不同类型的字段组合在一个名称下。

7. Algorithms | 算法

Algorithms are step‑by‑step procedures for solving problems. They can be expressed as flowcharts, pseudocode, or actual code. Key constructs are sequence, selection, and iteration.

算法是解决特定问题的分步过程。可用流程图、伪代码或实际代码表示。基本结构是顺序、选择和循环。

Searching algorithms: linear search checks each element one by one (works on unsorted data, O(n) time). Binary search repeatedly divides a sorted list in half, comparing the middle element (O(log n) time). Binary search is much faster on large datasets but requires the data to be sorted.

搜索算法：线性搜索逐个检查每个元素（适用于未排序数据，时间复杂度 O(n)）。二分查找反复将已排序列表对半分割，比较中间元素（时间复杂度 O(log n)）。二分查找在大数据集上快得多，但要求数据已排序。

Sorting algorithms: bubble sort repeatedly steps through the list, swapping adjacent elements if they are in the wrong order. It is simple but inefficient for large data (O(n²)). Merge sort divides the list into halves, recursively sorts them, and merges the sorted halves; it is more efficient (O(n log n)) but uses extra memory.

排序算法：冒泡排序重复遍历列表，若相邻元素顺序错误则交换。它简单但对大数据效率低下（O(n²)）。归并排序将列表分成两半，递归排序，再合并已排序的两半；效率更高（O(n log n)），但需要额外内存。

Trace tables are used to track variable values step by step through an algorithm, helping to identify logical errors. Flowchart symbols: oval for start/end, rectangle for process, diamond for decision, parallelogram for input/output, arrows for flow direction.

跟踪表用于逐步追踪算法执行过程中的变量值，帮助发现逻辑错误。流程图符号：椭圆表示开始/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，箭头表示流向。

8. System Software | 系统软件

System software manages hardware and provides a platform for application software. The operating system (OS) performs memory management, processor scheduling, file management, user interface, and peripheral management.

系统软件管理硬件并为应用软件提供平台。操作系统（OS）执行内存管理、处理器调度、文件管理、用户界面和外设管理。

Utility programs perform maintenance tasks: disk defragmentation (reorganises fragmented files on magnetic disks for speed), backup software, antivirus, compression tools, and file managers. These utilities enhance system performance and security.

实用工具程序执行维护任务：磁盘碎片整理（重新组织磁盘上碎片化的文件以提高速度）、备份软件、防病毒、压缩工具和文件管理器。这些实用程序可提升系统性能和安全性。

The OS provides a user interface — graphical (GUI), command‑line (CLI), or menu‑driven — to allow users to interact with the machine. Memory management ensures each process has enough memory and prevents processes from interfering with each other.

操作系统提供用户界面——图形界面（GUI）、命令行（CLI）或菜单驱动界面——让用户与机器交互。内存管理确保每个进程有足够内存，并防止进程相互干扰。

9. Ethical, Legal, and Environmental Impacts | 伦理、法律和环境影响

The digital divide refers to the gap between those who have access to modern digital technology and those who do not. It can be affected by geography, income, age, and education. Governments and organisations run initiatives to improve digital literacy and infrastructure.

数字鸿沟是指能访问现代数字技术者与不能访问者之间的差距。它可能受地域、收入、年龄和教育影响。政府和组织开展行动以提高数字素养和基础设施。

Legislation such as the Data Protection Act (DPA) and General Data Protection Regulation (GDPR) governs how personal data is collected, stored, and used. The Computer Misuse Act criminalises hacking and unauthorised access to computer systems. Copyright and patents protect intellectual property.

数据保护法（DPA）和通用数据保护条例（GDPR）等法律规范个人数据的收集、存储和使用方式。《计算机滥用法》将黑客行为和未经授权访问计算机系统定为犯罪。版权和专利保护知识产权。

Technology has environmental impacts: manufacturing devices consumes energy and rare materials; e‑waste poses disposal challenges. Positive contributions include energy‑efficient cloud computing, telecommuting reducing travel, and smart grids optimising energy usage. Sustainable design and recycling programmes are increasingly important.

技术对环境有影响：制造设备消耗能源和稀有材料；电子垃圾带来处置难题。积极贡献包括节能云计算、远程办公减少出行，以及智能电网优化能源使用。可持续设计和回收计划日益重要。

Artificial intelligence and automation raise ethical questions about bias, accountability, and job displacement. Stakeholders must balance innovation with social responsibility. As computer scientists, you should consider the wider impact of your work.

人工智能和自动化引发了关于偏见、问责和就业替代的伦理问题。利益相关者必须在创新与社会责任之间取得平衡。作为计算机科学家，你应该考虑自己工作的广泛影响。

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IGCSE AQA Computer Science: End-of-Term Revision Guide | IGCSE AQA 计算机科学：期末复习提纲