📚 GCSE WJEC Computer Science: End-of-Term Revision Guide | GCSE WJEC 计算机：期末复习提纲
This revision guide structures the key topics in the WJEC GCSE Computer Science specification into a clear, manageable checklist. It is designed to support your end-of-term preparation by highlighting fundamental concepts, technical vocabulary, and common exam question focuses. Refer back to your class notes and past papers as you work through each section.
本复习提纲将 WJEC GCSE 计算机科学考试大纲的关键主题整合成一份清晰、易于把握的检查清单，旨在帮助你进行期末备考，突出基本概念、技术术语和常见考点。请结合课堂笔记和历年真题逐一复习每个部分。
1. Computer Systems Architecture | 计算机系统架构
A computer follows the Von Neumann architecture, where the CPU, memory, and input/output devices are connected via buses. The CPU constantly cycles through fetching, decoding, and executing instructions.
计算机遵循冯·诺依曼架构，CPU、存储器和输入/输出设备通过总线连接。CPU 不断循环执行取指、译码和执行指令的过程。
The Control Unit (CU) directs operations, while the Arithmetic Logic Unit (ALU) performs calculations and logic. Key registers include the Program Counter (PC), Memory Address Register (MAR), Memory Data Register (MDR), and Accumulator (ACC).
控制单元（CU）指挥操作，算术逻辑单元（ALU）执行计算和逻辑运算。关键寄存器包括程序计数器（PC）、存储器地址寄存器（MAR）、存储器数据寄存器（MDR）和累加器（ACC）。
CPU performance is influenced by clock speed, the number of cores, and cache size. A higher clock speed means more instructions per second, multiple cores allow parallel processing, and larger cache reduces the time to access frequently used data.
CPU 性能受时钟速度、内核数量和缓存大小的影响。时钟速度越高，每秒执行的指令越多；多核支持并行处理；更大的缓存减少访问常用数据的时间。
An embedded system is a dedicated computer built into a larger device, such as a washing machine, microwave, or car engine control unit. It typically has a limited function, low power consumption, and real-time processing requirements.
嵌入式系统是内置在大型设备中的专用计算机，如洗衣机、微波炉或汽车引擎控制单元。它通常功能有限、功耗低，并需要实时处理。
2. Memory and Storage | 内存与存储
Primary memory consists of RAM and ROM. RAM is volatile and holds the operating system, programs, and data currently in use. ROM is non-volatile and contains the BIOS/bootstrap instructions needed to start the computer.
主存储器由 RAM 和 ROM 组成。RAM 是易失性的，存放当前使用的操作系统、程序和数据；ROM 是非易失性的，包含启动计算机所需的 BIOS / 引导指令。
Cache is a small amount of extremely fast memory located close to the CPU, used to store frequently accessed instructions and data. Virtual memory uses a portion of the hard drive as an extension of RAM when physical memory is full, but it is much slower.
缓存是位于 CPU 附近的小容量超高速存储器，用于存放频繁访问的指令和数据。虚拟内存则在物理内存不足时，将部分硬盘空间当作 RAM 使用，但速度慢得多。
Secondary storage includes magnetic hard disk drives (HDD), optical discs (CD, DVD), solid-state drives (SSD), and cloud storage. Each type varies in capacity, speed, durability, portability, and cost.
辅助存储包括磁性硬盘（HDD）、光盘（CD、DVD）、固态硬盘（SSD）和云存储。这些存储介质在容量、速度、耐用性、便携性和成本上各有不同。
Data storage units start from a bit (b) and progress through nibble (4 bits), byte (B, 8 bits), kilobyte (KB), megabyte (MB), gigabyte (GB), terabyte (TB) and petabyte (PB). For file sizes, 1 KB = 10³ bytes; for memory, 1 KiB = 2¹⁰ bytes, but GCSE typically uses the decimal convention.
数据存储单位从比特（b）开始，依次为半字节（4 bits）、字节（B，8 bits）、千字节（KB）、兆字节（MB）、吉字节（GB）、太字节（TB）和拍字节（PB）。文件大小中 1 KB = 10³ 字节；内存中 1 KiB = 2¹⁰ 字节，但 GCSE 通常使用十进制换算。
3. Data Representation | 数据表示
Computers use binary (base‑2). Denary (base‑10) numbers can be converted to binary by successive division by 2, noting remainders. Hexadecimal (base‑16) is used as a shorthand for binary, with each hex digit standing for 4 bits (a nibble).
计算机使用二进制（基数为 2）。十进制（基数为 10）数可通过不断除以 2 并记录余数转换为二进制。十六进制（基数为 16）用作二进制的简写，每个十六进制数字代表 4 个二进制位（半个字节）。
Binary arithmetic includes addition (with carry and overflow) and logical shifts (left shift multiplies by 2, right shift divides by 2). Overflow occurs when a calculation produces a result too large for the allocated number of bits.
二进制算术包括加法（带进位和溢出）以及逻辑移位（左移乘以 2，右移除以 2）。当计算结果超出分配的位数时，会发生溢出。
Text is represented using character sets: ASCII uses 7 bits to encode 128 characters, while extended ASCII uses 8 bits for 256. Unicode uses 16, 24, or 32 bits to represent characters from all major languages and symbols.
文本使用字符集表示：ASCII 用 7 位编码 128 个字符，扩展 ASCII 用 8 位表示 256 个。Unicode 使用 16 位、24 位或 32 位，可表示所有主要语言和符号的字符。
Images are made of pixels, with colour depth (bits per pixel) controlling how many colours can be displayed. Resolution (pixel count) and colour depth increase file size. Metadata stores image properties such as width, height, and colour palette.
图像由像素组成，颜色深度（每像素位数）决定可显示的颜色数。分辨率（像素数量）和颜色深度都会增加文件大小。元数据存储宽度、高度和调色板等图像属性。
Sound is sampled at regular intervals. The sampling rate (Hz) and bit depth determine the quality and file size. Higher sample rates and bit depths capture sound more accurately but create larger files.
声音通过定期采样转换为数字信号。采样率（赫兹）和位深度决定了音质和文件大小。更高的采样率和位深度能更准确地捕捉声音，但文件也更大。
Compression reduces file size. Lossy compression permanently removes some data (e.g., JPEG, MP3); lossless compression reduces size without losing any information (e.g., ZIP, PNG). Run‑length encoding (RLE) and Huffman coding are common lossless techniques.
压缩用于减小文件体积。有损压缩（如 JPEG、MP3）永久性地丢弃部分数据；无损压缩（如 ZIP、PNG）在缩减大小的同时不丢失任何信息。行程编码（RLE）和哈夫曼编码是常见的无损技术。
4. Networks and Communication | 网络与通信
A network can be a Local Area Network (LAN) covering a small geographical area, or a Wide Area Network (WAN) connecting LANs over large distances. The Internet is a global WAN.
网络可分为覆盖小范围地理区域的局域网（LAN）和连接远程局域网的广域网（WAN）。互联网是全球性的广域网。
Factors affecting network performance include bandwidth, latency, the number of connected devices, and transmission media (wired vs. wireless). Higher bandwidth allows more data to travel at once; lower latency means less delay.
影响网络性能的因素包括带宽、延迟、连接的设备数量和传输介质（有线与无线）。带宽越高，一次可传输的数据越多；延迟越低，延迟时间越短。
Client‑server networks have a central server providing resources, while peer‑to‑peer (P2P) networks allow each device to share resources directly without a central authority. Client‑server is easier to manage, P2P is cheaper and more resilient.
客户机-服务器网络由中央服务器提供资源；对等（P2P）网络则允许每台设备直接共享资源，没有中央管理者。客户机-服务器模式更易管理，P2P 更廉价且更具弹性。
Common network hardware includes switches (connect devices within a LAN and forward data intelligently), routers (connect networks and route packets), wireless access points (WAP), and network interface cards (NIC).
常见网络硬件包括交换机（在局域网内连接设备并智能转发数据）、路由器（连接不同网络并路由数据包）、无线接入点（WAP）和网络接口卡（NIC）。
Star topology connects all devices to a central switch; if one cable fails, only that device is affected. Mesh topology connects devices to many others for redundancy, improving reliability but increasing cost.
星型拓扑将所有设备连接到中央交换机；某根电缆故障只影响该设备。网状拓扑将设备与多个其他设备相连，提供冗余以提高可靠性，但成本更高。
Protocols are rules for communication. Key protocols: TCP/IP (transmission and routing), HTTP/HTTPS (web pages), FTP (file transfer), SMTP (sending email), POP3 and IMAP (receiving email). The TCP/IP model has four layers: Application, Transport, Internet, and Link.
协议是通信规则。关键协议：TCP/IP（传输和路由）、HTTP/HTTPS（网页）、FTP（文件传输）、SMTP（发送邮件）、POP3 和 IMAP（接收邮件）。TCP/IP 模型有四层：应用层、传输层、互联网层和链路层。
Every network device has a MAC address (unique physical identifier) and an IP address (logical address that can change). IPv4 uses 32‑bit addresses, while IPv6 uses 128‑bit addresses to solve address exhaustion.
每个网络设备都有 MAC 地址（唯一的物理标识）和 IP 地址（可变的逻辑地址）。IPv4 使用 32 位地址，IPv6 使用 128 位地址以解决地址枯竭问题。
5. Network Security | 网络安全
Malware includes viruses (attach to files, require user activation), worms (self‑replicate across networks), and Trojans (disguised as legitimate software). Phishing uses deceptive emails to steal personal information.
恶意软件包括病毒（附着文件、需用户激活）、蠕虫（在网络上自我复制）和特洛伊木马（伪装成合法软件）。网络钓鱼使用欺骗性电子邮件窃取个人信息。
Other threats: brute force attacks (trying many passwords), Denial of Service (DoS) attacks (flooding a server), and SQL injection (inserting malicious SQL code into database queries). Social engineering manipulates people into giving away confidential data.
其他威胁：暴力攻击（反复尝试密码）、拒绝服务（DoS）攻击（向服务器灌入大量请求）和 SQL 注入（插入恶意 SQL 代码）。社会工程学则操纵人们泄露机密信息。
Prevention methods include firewalls (filter traffic), encryption (scramble data), anti‑malware software, regular software updates, strong passwords and two‑factor authentication, physical security, and penetration testing to find vulnerabilities.
防护方法包括防火墙（过滤流量）、加密（扰乱数据）、反恶意软件、定期软件更新、强密码和双因素认证、物理安全以及通过渗透测试发现漏洞。
Network forensics involves monitoring and analysing network traffic to detect intrusions and investigate security breaches. Organisations must also have acceptable use policies and regular staff training.
网络取证包括监控和分析网络流量，以检测入侵并调查安全事件。组织还应制定可接受使用政策，并定期培训员工。
6. System Software | 系统软件
The operating system (OS) manages hardware and software resources. Key functions include memory management (allocating RAM to processes), process scheduling (multitasking), file management, handling input/output, and providing a user interface (GUI or CLI).
操作系统（OS）管理硬件和软件资源。其主要功能包括内存管理（为进程分配 RAM）、进程调度（实现多任务）、文件管理、处理输入/输出以及提供用户界面（图形界面或命令行界面）。
The OS also manages user accounts and security, ensuring that users can only access permitted files and resources. It provides an environment in which other software can run.
操作系统还管理用户账户和安全，确保用户只能访问被允许的文件和资源。它为其他软件的运行提供了环境。
Utility software performs specific maintenance tasks. Examples: encryption software, disk defragmentation, backup tools, file compression, disk cleanup, and anti‑malware utilities. Defragmentation reorganises fragmented files on a magnetic HDD to improve speed.
实用软件执行特定的维护任务，例如加密软件、磁盘碎片整理、备份工具、文件压缩、磁盘清理和反恶意软件工具。碎片整理重新组织磁性硬盘上的碎片文件以提高读写速度。
7. Ethical, Legal and Environmental Impact | 伦理、法律与环境影响
The Data Protection Act 2018 / GDPR governs how personal data may be collected, stored, and used. Key principles: data must be processed lawfully, fairly, and transparently; used only for specified purposes; kept accurate and secure; and held only as long as necessary.
《2018 年数据保护法》/ GDPR 规定了个人数据的收集、存储和使用方式。核心原则：数据必须合法、公平、透明地处理；仅用于指定目的；保持准确和安全；并仅保存至必需期限。
The Computer Misuse Act makes it an offence to access a computer without permission (unauthorised access), to access with intent to commit further crimes, and to impair the operation of a computer (e.g., spreading malware or DoS).
《计算机滥用法》规定，未经授权访问计算机（非法访问）、意图进一步犯罪而进行访问、以及破坏计算机运行（如传播恶意软件或 DoS）均属违法行为。
The Copyright, Designs and Patents Act protects original creative works, including software, music, and images. Software licensing determines how programs can be used: proprietary (closed source, purchased licence) vs open source (source code freely available and modifiable).
《版权、设计和专利法》保护原创作品，包括软件、音乐和图像。软件许可决定了程序的使用方式：专有软件（闭源，购买许可）与开源软件（源代码自由获取和修改）。
Technology has environmental impacts: manufacturing devices uses energy and rare materials; discarded electronics (e‑waste) create toxic waste; data centres and networks consume significant electricity. The “digital divide” highlights inequality in access to technology.
技术对环境有影响：制造设备消耗能源和稀有材料；废弃电子产品（电子垃圾）产生有毒废物；数据中心和网络耗电巨大。“数字鸿沟”体现了技术获取的不平等。
Cultural and privacy concerns arise from social media, mass surveillance, and facial recognition. Individuals must balance convenience with the right to privacy, while societies debate censorship and freedom of expression online.
社交媒体、大规模监控和人脸识别引发了文化和隐私问题。个人需在便利与隐私权之间取得平衡，而社会也在争论网络审查与言论自由。
8. Algorithms and Computational Thinking | 算法与计算思维
Computational thinking involves decomposition (breaking a problem down), pattern recognition, abstraction (focusing on key details), and algorithm design. These skills are assessed through flowcharts, pseudocode, and trace tables.
计算思维包括分解（将问题拆解）、模式识别、抽象（聚焦关键细节）和算法设计。这些技能通过流程图、伪代码和跟踪表来考查。
Searching algorithms: a linear search checks each item in order—simple but slow on large lists. A binary search works on a sorted list, repeatedly dividing the search interval in half, giving logarithmic time efficiency.
搜索算法：线性搜索按顺序逐一检查每个项——简单但在大列表上速度慢。二分搜索针对已排序列表，不断将搜索区间减半，具有对数级时间效率。
Sorting algorithms: bubble sort repeatedly steps through the list, swapping adjacent items if they are in the wrong order—it is intuitive but slow for large n. Insertion sort builds the sorted list one item at a time. Merge sort uses a divide‑and‑conquer approach and is more efficient.
排序算法：冒泡排序反复遍历列表，若相邻项顺序错误则交换——直观但数据量大时慢。插入排序一次将一个项插入到已排序部分。归并排序采用分治法，效率更高。
When tracing an algorithm with a trace table, you record the values of variables step by step. This helps identify logic errors and understand how an algorithm works. Be prepared to complete trace tables in the exam.
使用跟踪表跟踪算法时，需逐步记录变量的值。这有助于发现逻辑错误并理解算法的工作原理。考试中可能需要你填写跟踪表。
Flowcharts use standard symbols (ovals for start/stop, rectangles for processes, diamonds for decisions) to represent the flow of an algorithm. Pseudocode uses structured English to describe the steps without strict syntax.
流程图使用标准符号（椭圆表示开始/结束，矩形表示处理步骤，菱形表示判断）来描述算法的流程。伪代码使用结构化的自然语言描述步骤，无需严格语法。
9. Programming Fundamentals | 编程基础
Variables are named memory locations that store data, and their data type defines the kind of value held: integer, real/float, Boolean, character, or string. Constants are named values that cannot change during execution.
变量是存储数据的命名内存位置，其数据类型定义了所保存值的种类：整型、实型/浮点型、布尔型、字符或字符串。常量是在程序执行期间不可更改的命名值。
Program flow is controlled by sequence, selection (if…else, switch/case), and iteration (definite loops with FOR, indefinite loops with WHILE or REPEAT…UNTIL). Nested structures allow complex logic.
程序流程由顺序、选择（if…else、switch/case）和迭代（FOR 定义循环，WHILE 或 REPEAT…UNTIL 条件循环）控制。嵌套结构可实现更复杂的逻辑。
Operators include arithmetic (+, -, *, /, MOD, DIV), relational (==, !=, <, >, <=, >=), and logical (AND, OR, NOT). Integer division (DIV) and modulus (MOD) are particularly useful in algorithm problems.
运算符包括算术符（+、-、*、/、MOD、DIV）、关系符（==、!=、<、>、<=、>=）和逻辑符（AND、OR、NOT）。整数除法（DIV）和取模（MOD）在算法问题中尤为常用。
Strings are sequences of characters. Common operations: finding length, extracting substrings, concatenation, and conversion between types (e.g., string to integer). Arrays hold multiple values of the same type in indexed positions; 1D arrays are lists, 2D arrays are like tables.
字符串是字符序列，常见操作有：求长度、提取子串、拼接以及类型转换（如字符串转整数）。数组以索引位置存放同一类型的多个值；一维数组类似列表，二维数组类似表格。
Subprograms break a program into manageable blocks. Procedures perform a task without returning a value; functions perform a task and return a result. Parameters pass data in and out, keeping code modular and reusable.
子程序将程序分解为可管理的模块。过程执行任务但不返回值；函数执行任务并返回结果。参数用于传入和传出数据，使代码模块化且可复用。
File handling allows programs to read from and write to persistent storage. Typical steps: open the file, read or write data, and close the file. This is essential for storing data beyond a single run of the program.
文件处理使程序能够读写持久存储。典型步骤：打开文件、读取或写入数据、关闭文件。这对于在单次运行之外保存数据至关重要。
Robust programs use validation (range check, type check, presence check, format check) to prevent incorrect data entry, and verification (e.g., double entry) to ensure data matches the original source. Testing uses normal, boundary, and erroneous data.
健壮的程序使用验证（范围检查、类型检查、存在检查、格式检查）防止错误数据输入，并使用确认（如双重输入）来确保数据与原始来源一致。测试使用正常数据、边界数据和错误数据。
10. Software Development Life Cycle | 软件开发生命周期
The software development life cycle includes analysis (gathering requirements), design (planning interfaces and structures), implementation (coding), testing, deployment, and evaluation. Each phase has specific outputs and deliverables.
软件开发生命周期包括分析（收集需求）、设计（规划界面和结构）、实现（编码）、测试、部署和评估。每个阶段都有特定的产出和交付物。
Waterfall is a linear model where each stage is completed before the next begins. Agile/iterative methods develop the system in small increments, allowing frequent feedback and easier changes. Understanding their advantages helps you discuss appropriate project choices.
瀑布模型是线性模型，每个阶段完成后才进行下一阶段。敏捷/迭代方法以小的增量开发系统，允许频繁反馈和更易更改。了解各自优势有助于选择合适的项目开发方式。
Translators convert source code: a compiler translates high‑level code into machine code all at once, creating an executable. An interpreter translates and executes line‑by‑line. Assemblers convert assembly language into machine code.
翻译器将源代码转换为机器代码：编译器一次性将高级代码全部翻译为机器码，生成可执行文件；解释器逐行翻译并执行；汇编器将汇编语言转换为机器码。
Integrated Development Environments (IDEs) provide tools to help programmers: a code editor with syntax highlighting, error diagnostics, a run‑time environment, and a debugger. You should be able to identify features and explain how they aid productivity.
集成开发环境（IDE）提供帮助程序员的各种工具：带语法高亮的代码编辑器、错误诊断、运行时环境和调试器。你需要能识别这些功能并解释它们如何提高效率。
11. Exam Preparation Tips | 考试准备技巧
Start by reviewing the specification to ensure you have covered every topic. Create topic‑wise flashcards for key terms, definitions, and acronyms. Regularly attempt past paper questions under timed conditions to build familiarity with question styles.
首先复习考试大纲，确保覆盖所有主题。为主题制作抽认卡，记录关键术语、定义和缩写。定期在限时条件下练习
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