📚 Year 12 WJEC Computer Science: Core Knowledge Overview | WJEC计算机Year 12核心知识点梳理
This article provides a structured revision guide to the essential topics covered in the Year 12 WJEC Computer Science syllabus. It is designed to help students consolidate their understanding of core concepts, from data representation and computer architecture to algorithms and networking. Each section presents a concise explanation in English followed by its Chinese equivalent, ensuring clarity and bilingual support.
本文为Year 12 WJEC计算机科学课程的核心知识点梳理提供结构化复习指南。内容涵盖数据表示、计算机体系结构、算法和网络等关键专题，旨在帮助学生巩固对核心概念的理解。每个部分先以英文简明讲解核心内容，再配以中文对照，确保概念清晰，便于双语学习。
1. Fundamentals of Computer Systems | 计算机系统基础
A computer system takes inputs, processes data, and produces outputs. The central component is the processor, which follows the stored program concept: instructions and data are held in memory and fetched sequentially. Key elements include hardware (physical components) and software (programs). The von Neumann architecture uses a single memory space for both instructions and data, and a system bus to connect processor, memory and input/output devices.
计算机系统接收输入、处理数据并产生输出。核心部件是处理器，它遵循存储程序概念：指令和数据存放在内存中，按顺序取出执行。系统包含硬件（物理组件）和软件（程序）。冯·诺依曼架构使用单一存储空间同时存放指令和数据，并通过系统总线连接处理器、存储器和输入/输出设备。
- Input devices: keyboard, mouse, sensor
- 输出设备：显示器、打印机
- Storage: primary (RAM, ROM) and secondary (HDD, SSD)
- 存储：主存（RAM、ROM）和辅存（硬盘、固态盘）
2. Data Representation | 数据表示
All data in a computer is represented using binary digits (bits). A group of 8 bits forms a byte. Numbers can be represented as unsigned binary, signed binary (two’s complement), or floating point. Text is encoded using character sets like ASCII and Unicode. Images are stored as bitmaps, where each pixel is represented by a binary colour code; sound is stored as a series of amplitude samples. Data compression can be lossy (e.g. JPEG) or lossless (e.g. run-length encoding).
计算机中所有数据都以二进制位（比特）表示。8个比特组成一个字节。数值可采用无符号二进制、有符号二进制（二进制补码）或浮点数表示。文本通过字符集（如ASCII和Unicode）编码。图像以位图形式存储，每个像素用二进制颜色码表示；声音则以一系列振幅采样值存储。数据压缩分为有损（如JPEG）和无损（如游程编码）两种类型。
| Unit | Size |
|---|---|
| 1 bit | 0 or 1 |
| 1 nibble | 4 bits |
| 1 byte | 8 bits |
| 1 kilobyte (KB) | 10³ bytes |
| 1 megabyte (MB) | 10⁶ bytes |
3. Computer Organisation and Architecture | 计算机组成与结构
The processor consists of the arithmetic logic unit (ALU), the control unit (CU), and a set of registers. Key registers include the program counter (PC), memory address register (MAR), memory data register (MDR), current instruction register (CIR) and accumulator (ACC). The fetch-decode-execute cycle is the fundamental operation sequence: Fetch the instruction from memory address in PC, decode it in the CU, execute using ALU and registers. Performance is influenced by clock speed, number of cores, cache size, and data bus width.
处理器由算术逻辑单元（ALU）、控制单元（CU）和一组寄存器组成。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）、当前指令寄存器（CIR）和累加器（ACC）。取指-译码-执行周期是基本的操作序列：根据PC中的地址从存储器取指令，由CU译码，利用ALU和寄存器执行。处理器性能受时钟速度、核心数、缓存大小和数据总线宽度的影响。
Fetch → Decode → Execute → (repeat)
4. Systems Software | 系统软件
Systems software manages hardware and provides a platform for applications. The operating system (OS) performs memory management, processor scheduling, input/output control, file management, and provides a user interface. Utility software includes antivirus, disk defragmenter, backup tools, and file compression. Language translators – assemblers, compilers, and interpreters – convert source code into machine code. A compiler translates the whole program once, while an interpreter translates and executes line by line.
系统软件负责管理硬件并为应用程序提供运行平台。操作系统（OS）执行内存管理、处理器调度、输入/输出控制、文件管理，并提供用户界面。实用工具软件包括防病毒、磁盘碎片整理、备份工具和文件压缩软件。语言翻译器——汇编器、编译器和解释器——将源代码转换成机器码。编译器一次性翻译整个程序，而解释器则逐行翻译并执行。
5. Algorithms and Programming | 算法与编程
Algorithms can be expressed in pseudocode or flowcharts. Common search algorithms are linear search (O(n)) and binary search (O(log n)), which requires sorted data. Sorting algorithms include bubble sort, insertion sort, and merge sort. Bubble sort passes through the list comparing adjacent elements and swapping if out of order; merge sort divides the list into halves, recursively sorts, then merges. Algorithm efficiency is described using Big O notation, focusing on time and space complexity.
算法可用伪代码或流程图表达。常见搜索算法有线性搜索（时间复杂度O(n)）和二分搜索（O(log n)），后者要求数据有序。排序算法包括冒泡排序、插入排序和归并排序。冒泡排序反复遍历列表，比较相邻元素并在失序时交换；归并排序则将列表分成两半，递归排序后再合并。算法效率用大O符号描述，关注时间复杂度和空间复杂度。
6. Programming Techniques | 编程技术
Programming revolves around data types, variables, and control structures. Primitive data types include integer, real (float), character, string, and Boolean. Structured data types such as arrays (1D and 2D) and records allow grouping. The three basic programming constructs are sequence, selection (if-else, switch-case), and iteration (for, while, do-while loops). Subroutines (procedures and functions) enable modular design; parameters can be passed by value or by reference. Global and local variables affect scope.
编程围绕数据类型、变量和控制结构展开。基本数据类型包括整型、实型（浮点型）、字符型、字符串型和布尔型。结构化数据类型如数组（一维和二维）和记录允许组合数据。三种基本编程结构是顺序、选择（if-else、switch-case）和迭代（for、while、do-while循环）。子程序（过程和函数）支持模块化设计；参数传递可以按值或按引用进行。全局变量和局部变量影响作用域。
7. Networking | 网络
A network connects computing devices for resource sharing and communication. Types include LAN (local area) and WAN (wide area). The TCP/IP protocol stack underpins internet communication: application layer (HTTP, FTP, SMTP), transport layer (TCP, UDP), internet layer (IP), and network access layer. Key hardware: routers, switches, hubs, and network interface cards (NIC). IP addresses (IPv4 and IPv6) uniquely identify devices; subnet masks separate network and host portions. Common topologies are star and mesh.
网络连接计算设备以实现资源共享和通信。网络类型包括局域网（LAN）和广域网（WAN）。TCP/IP协议栈是互联网通信的基础：应用层（HTTP、FTP、SMTP）、传输层（TCP、UDP）、网际层（IP）和网络接入层。关键硬件：路由器、交换机、集线器和网络接口卡（NIC）。IP地址（IPv4和IPv6）唯一标识设备；子网掩码区分网络部分和主机部分。常见拓扑有星型和网状。
8. Databases | 数据库
A relational database organises data into tables with rows (records) and columns (fields). Each table has a primary key that uniquely identifies each record. Foreign keys establish relationships between tables. Normalisation (1NF, 2NF, 3NF) reduces data redundancy and anomalies. SQL (Structured Query Language) is used to query and manipulate data; common commands include SELECT, INSERT, UPDATE, DELETE, and JOIN. Referential integrity ensures foreign key values match existing primary keys.
关系数据库将数据组织为表，表由行（记录）和列（字段）组成。每个表都有一个主键，用于唯一标识每条记录。外键用于在表之间建立关系。范式化（1NF、2NF、3NF）减少数据冗余和异常。SQL（结构化查询语言）用于查询和操作数据；常用命令包括SELECT、INSERT、UPDATE、DELETE和JOIN。引用完整性确保外键值与现存主键匹配。
9. Computational Thinking | 计算思维
Computational thinking is a problem-solving approach that involves decomposition (breaking down a complex problem into smaller parts), pattern recognition (identifying similarities), abstraction (removing unnecessary detail), and algorithm design (developing step-by-step solutions). These skills are essential for writing efficient programs and are embedded throughout the WJEC course, including in programming projects and theoretical exam questions.
计算思维是一种解决问题的方法，包括分解（将复杂问题拆分为更小的部分）、模式识别（找出相似性）、抽象（去除不必要细节）和算法设计（制定逐步解决方案）。这些技能对于编写高效的程序至关重要，并贯穿WJEC课程的始终，包括编程项目和理论考试问题。
10. Legal, Ethical and Environmental Issues | 法律、伦理与环境问题
Computer use is governed by legislation such as the Data Protection Act (GDPR), which regulates the storage and processing of personal data, and the Computer Misuse Act, which criminalises unauthorised access to computer material. Copyright and intellectual property laws protect software and digital content. Ethical considerations include digital divide, censorship, and the impact of automation on employment. Environmentally, the life cycle of hardware involves energy consumption, resource depletion, and e-waste; recycling and green computing aim to mitigate these effects.
计算机使用受到诸如《数据保护法》（GDPR）等立法的约束，该法规范个人数据的存储和处理；《计算机滥用法》则将未经授权访问计算机资料定为犯罪。版权和知识产权法保护软件和数字内容。伦理考量包括数字鸿沟、审查制度和自动化对就业的影响。在环境方面，硬件的生命周期涉及能源消耗、资源枯竭和电子垃圾；回收利用和绿色计算旨在减轻这些影响。
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