📚 A-Level Computer Science: End-of-Term Revision Outline | A-Level 计算机：期末复习提纲
This comprehensive revision guide covers the essential topics for A-Level Computer Science. It serves as a structured review to help you consolidate key concepts, from hardware and data representation to algorithms and ethical issues. Use it to check your understanding and identify areas needing further study before the final examination.
这份全面的复习指南涵盖了 A-Level 计算机科学的基本主题。它是一个结构化的复习方案，帮助您巩固从硬件和数据表示到算法和伦理问题等关键概念。请在期末考试前使用它来检查您的理解并确定需要进一步学习的领域。
1. Computer Systems and Architecture | 计算机系统与架构
Understanding the Von Neumann architecture is fundamental. A typical system includes a CPU with an ALU, control unit (CU), and registers such as the Program Counter (PC), Memory Address Register (MAR), and Memory Data Register (MDR).
理解冯·诺依曼体系结构是基础。典型系统包括一个带有 ALU、控制单元（CU）以及程序计数器（PC）、存储器地址寄存器（MAR）和存储器数据寄存器（MDR）等寄存器的 CPU。
The fetch-decode-execute cycle describes how instructions are processed. The CPU fetches an instruction from memory, decodes it, and then executes it, continuously repeating.
取指-译码-执行周期描述了指令的处理方式。CPU 从内存中取出一条指令，对其进行译码，然后执行，如此不断重复。
Factors affecting CPU performance include clock speed, number of cores, and cache size. Pipelining can increase throughput by overlapping instruction stages.
影响 CPU 性能的因素包括时钟速度、核心数和缓存大小。流水线技术可以通过重叠指令阶段来提高吞吐量。
Embedded systems are specialised computers designed for a specific task, often with limited resources, contrasting with general-purpose systems.
嵌入式系统是为特定任务设计的专用计算机，通常资源有限，与通用系统形成对比。
2. Data Representation | 数据表示
Numbers are represented in binary, using bits. Unsigned binary, two’s complement for negative numbers, and floating-point representation for real numbers are essential.
数字用二进制位表示。无符号二进制、用于负数的补码以及用于实数的浮点表示是必不可少的。
Two’s complement allows representation of negative integers by inverting bits and adding 1. For example, the 8-bit two’s complement of -5 is 11111011₂.
补码通过反转位并加 1 来表示负整数。例如，-5 的 8 位补码是 11111011₂。
Floating-point numbers use a mantissa and exponent, often following the IEEE 754 standard. Understand normalisation to maximise precision.
浮点数使用尾数和指数，通常遵循 IEEE 754 标准。理解归一化以最大化精度。
Character representation: ASCII uses 7 or 8 bits, while Unicode extends to accommodate global scripts, using encodings like UTF-8.
字符表示：ASCII 使用 7 或 8 位，而 Unicode 扩展了以适应全球文字，使用 UTF-8 等编码。
Image representation – bitmap images store pixel colour values, often with colour depth and resolution. Vector graphics store drawing instructions.
图像表示 – 位图图像存储像素颜色值，通常包含色彩深度和分辨率。矢量图形存储绘图指令。
Sound representation uses sampling, where analogue signals are measured at intervals (sample rate) and quantised (bit depth).
声音表示使用采样，在间隔（采样率）处测量模拟信号并量化（位深度）。
Data compression: lossless (e.g., run-length encoding, Huffman coding) preserves all data, while lossy (e.g., JPEG, MP3) sacrifices some fidelity for higher compression.
数据压缩：无损压缩（如行程编码、霍夫曼编码）保留所有数据，而有损压缩（如 JPEG、MP3）牺牲一些保真度以获得更高的压缩率。
3. Computer Networks | 计算机网络
Networks can be categorized by scale: LAN (Local Area Network) and WAN (Wide Area Network). Topologies include star, bus, ring, and mesh, each with advantages in cost, reliability, and scalability.
网络可按规模分类：LAN（局域网）和 WAN（广域网）。拓扑结构包括星型、总线型、环型和网状，各有成本、可靠性和可扩展性方面的优点。
The TCP/IP stack comprises layers: Application, Transport, Internet, and Network Access. Each layer provides services to the layer above using protocols such as HTTP, TCP, IP, and Ethernet.
TCP/IP 协议栈包括应用层、传输层、互联网层和网络接入层。每一层使用 HTTP、TCP、IP 和以太网等协议向上层提供服务。
Common protocols: HTTP/HTTPS for web, FTP for file transfer, SMTP/POP3/IMAP for email, and DNS for domain name resolution. Understand client-server and peer-to-peer models.
常见协议：用于 Web 的 HTTP/HTTPS、用于文件传输的 FTP、用于电子邮件的 SMTP/POP3/IMAP，以及用于域名解析的 DNS。理解客户-服务器和对等网络模型。
Network security measures include firewalls, encryption (symmetric and asymmetric), and MAC address filtering. Threats such as malware, phishing, and DoS attacks should be recognized.
网络安全措施包括防火墙、加密（对称和非对称）和 MAC 地址过滤。应识别恶意软件、钓鱼和 DoS 攻击等威胁。
Packet switching breaks data into packets that travel independently across the network. Routers use IP addresses to forward packets.
分组交换将数据分割成分组，这些分组独立地在网络中传输。路由器使用 IP 地址转发分组。
4. Databases and SQL | 数据库与 SQL
Relational databases store data in tables with rows and columns. Primary keys uniquely identify each record, while foreign keys establish relationships between tables.
关系数据库将数据存储在具有行和列的表中。主键唯一标识每条记录，而外键建立表之间的关系。
Normalisation reduces data redundancy and improves integrity. First Normal Form (1NF) eliminates repeating groups; 2NF removes partial dependencies; 3NF removes transitive dependencies.
规范化减少数据冗余并提高完整性。第一范式（1NF）消除重复组；2NF 消除部分依赖；3NF 消除传递依赖。
SQL is used to query and manipulate data. Basic commands: SELECT, FROM, WHERE, INSERT, UPDATE, DELETE. JOIN clauses combine data from multiple tables.
SQL 用于查询和操作数据。基本命令：SELECT、FROM、WHERE、INSERT、UPDATE、DELETE。JOIN 子句组合来自多个表的数据。
Example query: SELECT student.name, course.title FROM student INNER JOIN enrollment ON student.id = enrollment.student_id INNER JOIN course ON course.id = enrollment.course_id;
查询示例：SELECT student.name, course.title FROM student INNER JOIN enrollment ON student.id = enrollment.student_id INNER JOIN course ON course.id = enrollment.course_id;
5. Programming Fundamentals | 编程基础
Programming paradigms: imperative/procedural, object-oriented (OOP), and declarative/functional. OOP concepts include classes, objects, inheritance, encapsulation, and polymorphism.
编程范式：命令式/过程式、面向对象（OOP）和声明式/函数式。OOP 概念包括类、对象、继承、封装和多态。
Data types: integer, float, Boolean, character, string, arrays/lists. Understand variable scope (local vs global) and constants.
数据类型：整数、浮点数、布尔值、字符、字符串、数组/列表。理解变量作用域（局部与全局）和常量。
Control structures: sequence, selection (if-else, switch-case), and iteration (for, while, do-while loops). Nested structures allow complex logic.
控制结构：顺序、选择（if-else、switch-case）和迭代（for、while、do-while 循环）。嵌套结构允许复杂逻辑。
Functions/procedures and parameter passing (by value and by reference). Recursion: a function calling itself with a base case to avoid infinite loops.
函数/过程和参数传递（按值传递和按引用传递）。递归：一个函数调用自身，并具有基本情况以避免无限循环。
File handling: opening, reading, writing, and closing files. Exception handling using try-catch blocks to manage runtime errors.
文件处理：打开、读取、写入和关闭文件。使用 try-catch 块进行异常处理以管理运行时错误。
6. Algorithms and Problem-Solving | 算法与问题求解
Algorithm design strategies: divide and conquer, greedy algorithms, dynamic programming, and backtracking. Analyse efficiency using Big O notation (e.g., O(n), O(log n), O(n²)).
算法设计策略：分治法、贪心算法、动态规划和回溯。使用大 O 记号分析效率（例如 O(n)、O(log n)、O(n²)）。
Searching algorithms: linear search (O(n)) and binary search (O(log n), requires sorted data). Compare their performance.
搜索算法：线性搜索（O(n)）和二分搜索（O(log n)，需要排序数据）。比较它们的性能。
Sorting algorithms: bubble sort (O(n²)), insertion sort (O(n²)), merge sort (O(n log n)), and quick sort (average O(n log n)). Know their mechanisms and stability.
排序算法：冒泡排序（O(n²)）、插入排序（O(n²)）、归并排序（O(n log n)）和快速排序（平均 O(n log n)）。了解它们的机制和稳定性。
Graph traversal: depth-first search (DFS) uses a stack; breadth-first search (BFS) uses a queue. Dijkstra’s algorithm finds the shortest path in weighted graphs.
图遍历：深度优先搜索（DFS）使用栈；广度优先搜索（BFS）使用队列。迪杰斯特拉算法在加权图中寻找最短路径。
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