📚 Year 12 WJEC Computing: Core Concepts Revision Guide | WJEC 12年级计算机：核心知识点梳理
Welcome to this focused revision resource for Year 12 WJEC Computer Science. Whether you are preparing for Unit 1 (Fundamentals of Computer Science) or strengthening the programming skills needed for Unit 2, this guide organises the key concepts into clear, manageable sections. We cover everything from binary arithmetic to ethical computing, with parallel English and Chinese explanations to support bilingual learners.
欢迎查阅这篇针对WJEC 12年级计算机科学的精讲复习指南。无论你正在备考单元一（计算机科学基础）还是巩固单元二所需的编程技能，本文都将核心知识点整理成清晰的模块。我们涵盖从二进制算术到计算机伦理学的一切内容，并以中英对照的方式帮助双语学习者加深理解。
1. Data Representation | 数据表示
All data inside a computer is stored and processed in binary (base‑2). The smallest unit is a bit, and 8 bits form a byte.
计算机内部所有数据都以二进制（基数为2）的形式存储和处理。最小单位是比特，8个比特组成一个字节。
Denary (base‑10) values can be converted to binary by successive division by 2, recording remainders in reverse order. For example, 45₁₀ becomes 101101₂.
十进制（基数为10）数值可以通过连续除以2并逆序记录余数转换为二进制。例如，45₁₀ 转换为 101101₂。
Hexadecimal (base‑16) compresses four bits into one symbol (0‑9, A‑F). It is widely used to represent colours, memory addresses, and machine code.
十六进制（基数为16）将四个比特压缩为一个符号（0‑9, A‑F）。它广泛用于表示颜色、内存地址和机器码。
To convert binary to hex, split the binary string into nibbles (groups of 4) and replace each nibble with its hex equivalent. For instance, 1101 0111₂ becomes D7₁₆.
要将二进制转换为十六进制，先把二进制串分成半字节（4位一组），再用十六进制符号替换每个半字节。例如，1101 0111₂ 变成 D7₁₆。
Negative integers are stored using two's complement. The most significant bit indicates the sign, and the negative value is found by inverting all bits and adding 1.
负整数采用补码（two's complement）存储。最高位指示符号，负数可以通过将所有位取反再加1得到。
=0, 0+1=1, 1+1=0 carry 1. Overflow occurs when the result exceeds the bit width available.
二进制加法遵循 0+0=0, 0+1=1, 1+1=0 进位1 的规则。当结果超出可用位宽时，会产生溢出。
Logical shifts (left and right) multiply or divide unsigned binary numbers by powers of two. A left shift by n positions multiplies by 2ⁿ; a logical right shift does unsigned division.
逻辑移位（左移和右移）将无符号二进制数乘以或除以2的幂。左移n位相当于乘以2ⁿ；逻辑右移实现无符号除法。
Character encoding maps characters to numeric codes. ASCII uses 7‑bits (128 characters), while Unicode (e.g., UTF‑8) supports a vast range of global scripts and emoji.
字符编码将字符映射为数字码。ASCII使用7位（128个字符），而Unicode（如UTF‑8）支持海量的全球文字和表情符号。
Images are stored as bitmaps, with each pixel's colour represented by a binary code. Colour depth (bits per pixel) determines how many colours can be displayed.
图像以位图形式存储，每个像素的颜色由二进制代码表示。颜色深度（每像素位数）决定了可以显示的颜色数量。
Sound is digitised by sampling the amplitude of an analogue wave at regular intervals. Sample rate and bit depth affect the quality and file size of the audio.
声音通过以固定间隔对模拟波形的振幅进行采样来实现数字化。采样率和位深度会影响音频的质量和文件大小。
Image file size (bits) = width × height × colour depth
Sound file size (bits) = sample rate × bit depth × duration (seconds) × channels
2. CPU and Computer Architecture | CPU 与计算机体系结构
The Central Processing Unit (CPU) is the brain of the computer. It follows the Von Neumann architecture, where both data and instructions are stored in the same memory.
中央处理器（CPU）是计算机的大脑。它遵循冯·诺依曼体系结构，其中数据和指令存放在同一内存中。
The CPU consists of three main components: the Control Unit (CU) that decodes instructions, the Arithmetic Logic Unit (ALU) that performs calculations, and a set of registers.
CPU 由三个主要部分组成：控制单元（CU）负责解码指令，算术逻辑单元（ALU）执行计算，以及一组寄存器。
Key registers include the Program Counter (PC) holding the address of the next instruction, the Memory Address Register (MAR), Memory Data Register (MDR), and the Accumulator (ACC).
关键寄存器包括：程序计数器（PC）存放下一条指令的地址，内存地址寄存器（MAR），内存数据寄存器（MDR）和累加器（ACC）。
The fetch‑decode‑execute cycle describes how the CPU continuously retrieves an instruction from memory, decodes it, and then executes it. This cycle repeats billions of times per second.
取指-解码-执行周期描述了 CPU 如何不断从内存中取出指令、解码并执行。这个周期每秒钟重复数十亿次。
CPU performance is influenced by clock speed (GHz), number of cores, and cache size. A higher clock speed means more cycles per second; multiple cores allow true parallel processing.
CPU 性能受时钟频率（GHz）、核心数和高速缓存大小的影响。更高的时钟频率意味着每秒更多周期；多核心允许真正的并行处理。
Cache memory is a small, very fast memory located close to the CPU. It stores frequently used instructions and data to reduce the average access time.
高速缓存是靠近 CPU 的小容量、极快速存储器。它存放频繁使用的指令和数据，以缩短平均访问时间。
Embedded systems are dedicated computers built into larger devices (e.g., microwaves, cars). They are compact, energy‑efficient, and run a specific program stored in ROM.
嵌入式系统是集成在大型设备（如微波炉、汽车）中的专用计算机。它们体积小、低功耗，并运行存储在 ROM 中的特定程序。
3. Memory and Storage | 内存与存储器
Primary memory consists of RAM (Random Access Memory) and ROM (Read Only Memory). RAM is volatile, losing its contents when power is off; ROM is non‑volatile and stores the boot program (BIOS).
主存储器包括 RAM（随机存取存储器）和 ROM（只读存储器）。RAM 是易失性的，断电后内容丢失；ROM 是非易失性的，存放引导程序（BIOS）。
Virtual memory uses part of the hard disk as an extension of RAM when physical memory is full. This can degrade performance due to slower disk speeds.
虚拟内存在物理内存不足时将部分硬盘用作 RAM 的扩展。由于硬盘速度较慢，这可能会降低性能。
Secondary storage is non‑volatile and includes magnetic (HDD), solid‑state (SSD), and optical (CD, DVD) media. SSDs are faster, more durable, but more expensive per GB than HDDs.
辅助存储器是非易失性的，包括磁介质（HDD）、固态（SSD）和光盘（CD、DVD）。SSD 速度更快、更耐用，但每 GB 成本高于 HDD。
Factors for choosing storage include capacity, speed, portability, durability, and cost. Cloud storage offers remote access but relies on internet connectivity.
选择存储设备时要考虑容量、速度、便携性、耐用性和成本。云存储提供远程访问，但依赖互联网连接。
²⁰ bytes, 1 GiB = 2³⁰ bytes. Manufacturers often use decimal prefixes (1 KB = 1000 bytes).
数据容量单位遵循2的幂：1 KiB = 2¹⁰ 字节，1 MiB = 2²⁰ 字节，1 GiB = 2³⁰ 字节。制造商通常使用十进制前缀（1 KB = 1000 字节）。
Number of addressable locations = 2 n, where n is the width of the address bus
4. Systems Software and Operating Systems | 系统软件与操作系统
The operating system (OS) manages hardware resources and provides a platform for applications. Core functions include memory management, process scheduling, file management, and user interface.
操作系统（OS）管理硬件资源并为应用程序提供平台。核心功能包括内存管理、进程调度、文件管理和用户界面。
Memory management ensures each process has its own memory space and handles virtual memory paging. This prevents programs from interfering with each other.
内存管理确保每个进程拥有自己的内存空间，并处理虚拟内存分页。这可以阻止程序之间相互干扰。
Peripheral management is achieved through device drivers, which translate OS commands into hardware‑specific instructions. Drivers allow the OS to communicate with printers, graphics cards, etc.
外设管理通过设备驱动程序实现，驱动程序将操作系统命令转换为特定硬件的指令。驱动程序使操作系统可以与打印机、显卡等通信。
Utility software performs maintenance tasks: disk defragmentation reorganises fragmented files for faster access, encryption tools secure data, and backup software creates copies to prevent loss.
实用软件执行维护任务：磁盘碎片整理重组碎片文件以加快访问，加密工具保护数据，备份软件创建副本以防丢失。
Antivirus and firewall software defend against malware and unauthorised network access. A firewall monitors incoming and outgoing traffic based on predetermined security rules.
防病毒和防火墙软件防御恶意软件和未经授权的网络访问。防火墙根据预设的安全规则监控进出站流量。
5. Networks and Network Security | 网络与网络安全
A network is two or more connected devices that can share resources. LANs cover a small geographical area, while WANs connect networks across cities or countries.
网络由两台或以上可共享资源的连接设备组成。局域网（LAN）覆盖较小地域，而广域网（WAN）连接跨城市或国家的网络。
Network topologies include star (central switch/hub), bus (single backbone cable), and mesh (multiple redundant connections). The star topology is common in modern Ethernet LANs.
网络拓扑结构包括星型（中央交换机/集线器）、总线型（单一主干线缆）和网状（多条冗余连接）。星型拓扑在现代以太网局域网中十分常见。
Protocols are rules governing data communication. Ethernet defines how data is framed for LANs, TCP/IP ensures reliable delivery across the internet, and HTTP/HTTPS handles web traffic.
协议是管理数据通信的规则。以太网定义了局域网的数据帧格式，TCP/IP 确保互联网上可靠传输，HTTP/HTTPS 处理网页流量。
The TCP/IP stack consists of four layers: Application, Transport, Internet, and Network Access. Each layer adds its own header to the data being transmitted.
TCP/IP 协议栈由四层构成：应用层、传输层、互联网层和网络接入层。每一层都会为要传输的数据添加自己的报头。
Common security threats include malware (viruses, worms, trojans), phishing (fraudulent emails to steal credentials), and denial‑of‑service (DoS) attacks that flood a server with traffic.
常见的安全威胁包括恶意软件（病毒、蠕虫、木马）、网络钓鱼（欺诈性邮件窃取凭证）以及拒绝服务攻击（DoS，用流量淹没服务器）。
Encryption scrambles data using an algorithm and a key. Symmetric encryption uses the same key for both encryption and decryption; asymmetric encryption uses a public‑private key pair.
加密利用算法和密钥打乱数据。对称加密使用相同密钥进行加密和解密；非对称加密使用公钥-私钥对。
6. The Internet and Communication | 互联网与通信
The Internet is a global network of networks. Data is split into packets that are routed independently and reassembled at the destination. Packet switching is efficient and fault‑tolerant.
互联网是网络的全球互联网络。数据被分割成数据包独立路由，并在目的地重新组装。分组交换高效且具有容错能力。
IP addresses (IPv4: 32‑bit, e.g., 192.168.1.1; IPv6: 128‑bit) uniquely identify devices on the network. DNS (Domain Name System) translates human‑readable domain names into IP addresses.
IP 地址（IPv4：32位，如 192.168.1.1；IPv6：128位）唯一标识网络上的设备。DNS（域名系统）将人类可读的域名转换为 IP 地址。
HTTP (Hypertext Transfer Protocol) is the foundation of data communication for the web. HTTPS adds SSL/TLS encryption for secure transactions.
HTTP（超文本传输协议）是网页数据通信的基础。HTTPS 增加了 SSL/TLS 加密以实现安全事务。
Cloud computing delivers services—storage, servers, software—over the internet. Benefits include scalability, reduced capital cost, and accessibility from any device.
云计算通过互联网提供存储、服务器、软件等服务。其优点包括可扩展性、降低资本支出以及可从任何设备访问。
The Internet of Things (IoT) refers to everyday objects embedded with sensors and connectivity, enabling them to send and receive data. Examples include smart thermostats and wearable fitness trackers.
物联网（IoT）指嵌入了传感器和连接功能的日常物品，能够收发数据。例子包括智能恒温器和可穿戴健身追踪器。
7. Algorithm Design and Problem‑Solving | 算法设计与问题求解
An algorithm is a step‑by‑step procedure to solve a problem. It can be expressed using pseudocode (informal, language‑like) or flowcharts (standard symbols: ovals for start/end, diamonds for decisions).
算法是解决问题的一步步过程。它可以用伪代码（非正式、类似语言）或流程图（标准符号：椭圆表示开始/结束，菱形表示判断）来表示。
Sequence, selection (IF…ELSE), and iteration (WHILE, FOR loops) are the three basic control structures that form any algorithm.
顺序、选择（IF…ELSE）和迭代（WHILE、FOR 循环）是构成任何算法的三大基本控制结构。
Searching algorithms: Linear search checks each element one‑by‑one until the target is found. Binary search repeatedly divides a sorted list in half, comparing the middle element with the target.
搜索算法：线性搜索逐个检查每个元素直到找到目标。二分搜索则在已排序列表中反复对半划分，将中间元素与目标进行比较。
Sorting algorithms: Bubble sort compares adjacent items and swaps them if they are in the wrong order, repeating until sorted. Insertion sort builds a sorted sublist by inserting each unsorted item into its correct position.
排序算法：冒泡排序比较相邻项，若顺序错误则交换，重复直至有序。插入排序通过将每个未排序项插入到已排序子列表的正确位置来构建有序序列。
Algorithm efficiency is often measured by time complexity. A linear search has O(n), binary search O(log n), bubble sort O(n²). This helps predict performance with large datasets.
算法效率通常用时间复杂度衡量。线性搜索为 O(n)，二分搜索为 O(log n)，冒泡排序为 O(n²)。这有助于预测大数据集时的性能。
Trace tables are used to dry‑run an algorithm, recording variable values step by step to find logical errors.
跟踪表用于手工执行算法，逐步记录变量值以发现逻辑错误。
8. Programming Fundamentals | 编程基础
Variables store data values and have an identifier, data type, and value. Common data types include integer, real (float), boolean, character, and string.
变量存储数据值，具有标识符、数据类型和值。常见的数据类型包括整数、实数（浮点数）、布尔值、字符和字符串。
Constants are named memory locations whose values cannot be changed during program execution. They improve readability and maintainability.
常量是命名的内存位置，其值在程序执行期间不可更改。它们提高了可读性和可维护性。
Operators: Arithmetic (+, -, *, /, MOD, DIV), comparison (==, ! <, >, <=, >=), and Boolean/logical operators (AND, OR, NOT) are used to build expressions.
运算符：算术（+、-、*、/、MOD、DIV）、比较（==、!=、<、>、<=、>=）和布尔/逻辑运算符（AND、OR、NOT）用于构建表达式。
Sequence is the default flow where statements are executed one after the other. Selection uses IF, ELSE IF, ELSE, or CASE statements to branch. Iteration repeats a block with WHILE, REPEAT…UNTIL, or FOR.
顺序是默认流程，语句逐条执行。选择使用 IF、ELSE IF、ELSE 或 CASE 语句进行分支。迭代使用 WHILE、REPEAT…UNTIL 或 FOR 重复执行代码块。
Subroutines (procedures and functions) promote modularity. Procedures perform a task without returning a value; functions return a value. Parameters pass data into subroutines.
子程序（过程和函数）促进模块化。过程执行任务但不返回值；函数返回一个值。参数将数据传入子程序。
Scope determines the visibility of variables. Local variables are accessible only within their subroutine; global variables can be accessed throughout the program.
作用域决定变量的可见性。局部变量只能在其子程序内访问；全局变量可在整个程序中访问。
9. Data Structures and Data Manipulation | 数据结构与数据操作
An array is a collection of elements of the same data type, stored contiguously in memory. Elements are accessed by their index, usually starting from 0.
数组是同一数据类型元素的集合，在内存中连续存储。元素通过索引访问，通常从0开始。
Two‑dimensional arrays (matrices) are arrays of arrays, used to represent grids or tables. Access requires row and column indices.
二维数组（矩阵）是数组的数组，用于表示网格或表格。访问需要行索引和列索引。
A record is a data structure that groups different types of data together under field names, like a single row in a database. It can store related attributes of an entity.
记录是一种数据结构，它将不同类型的数据按字段名组合在一起，就像数据库中的一行。它可以存储实体的相关属性。
Data validation checks data input against rules (range check, presence check, format check) to ensure it is sensible. Data verification checks for accuracy, often by double entry or proofreading.
数据验证根据规则（范围检查、存在检查、格式检查）检查输入数据以确保其合理。数据核实通过双重录入或校对检查准确性。
File handling involves opening, reading, writing, and closing files. Sequential files are accessed linearly, while random‑access files allow direct access to any record.
文件处理包括打开、读取、写入和关闭文件。顺序文件线性访问，而随机访问文件允许直接访问任意记录。
10. Database Concepts and SQL | 数据库概念与 SQL
A database is a structured collection of data. A relational database organises data into tables (relations), where each table has rows (records) and columns (fields).
数据库是结构化数据集合。关系数据库将数据组织成表（关系），每个表包含行（记录）和列（字段）。
A primary key is a field that uniquely identifies each record in a table. A foreign key links one table to the primary key of another, forming relationships.
主键是唯一标识表中每条记录的一个字段。外键将一个表与另一个表的主键关联，形成关系。
SQL (Structured Query Language) is used to manage and query databases. The SELECT statement retrieves data: SELECT field1, field2 FROM table WHERE condition;
SQL（结构化查询语言）用于管理和查询数据库。SELECT 语句检索数据：SELECT field1, field2 FROM table WHERE condition;
Data manipulation uses INSERT INTO to add rows, UPDATE to modify existing data, and DELETE FROM to remove records. Conditions ensure only intended rows are affected.
数据操作使用 INSERT INTO 添加行，UPDATE 修改现有数据，DELETE FROM 删除记录。条件确保仅影响预期的行。
Queries can be refined with ORDER BY (sorting), DISTINCT (removing duplicates), and aggregate functions like COUNT, SUM, AVG, MAX, MIN.
查询可以用 ORDER BY（排序）、DISTINCT（去除重复）以及聚合函数如 COUNT、SUM、AVG、MAX、MIN 进行细化。
Entity‑relationship diagrams (ERDs) model databases visually, showing entities as rectangles, attributes as ovals, and relationships as connecting lines.
实体关系图（ERD）以可视化方式建模数据库，实体表示为矩形，属性为椭圆，关系为连接线。
11. Ethical, Legal and Environmental Issues | 伦理、法律与环境问题
The Data Protection Act (DPA/2018) governs how personal data is collected, stored, and used. It requires data to be processed fairly, lawfully, and for specified purposes.
《数据保护法》（DPA/2018）规范了个人数据的收集、存储和使用方式。它要求数据处理必须公平、合法且用于明确目的。
The Computer Misuse Act (CMA) criminalises unauthorised access to computer systems, including hacking and malware distribution. Offences include accessing with intent to commit further crimes.
《计算机滥用法》（CMA）将未经授权访问计算机系统（包括黑客攻击和恶意软件传播）定为犯罪。罪行包括为实施进一步犯罪而进行访问。
The Copyright, Designs and Patents Act protects intellectual property in software, music, and digital content. It prevents unauthorised copying and distribution.
《版权、外观设计和专利法》保护软件、音乐和数字内容的知识产权。它防止未经授权的复制和分发。
Environmental concerns relate to the energy consumption of data centres, e‑waste from discarded devices, and the carbon footprint of manufacturing. Responsible recycling and energy‑efficient design are critical.
环境问题涉及数据中心的能耗、废弃设备产生的电子垃圾，以及制造过程中的碳足迹。负责任的回收和节能设计至关重要。
Ethical computing also covers online behaviour, privacy, and the digital divide. Users and developers should act with honesty and respect for others' rights.
计算机伦理还涵盖线上行为、隐私和数字鸿沟。用户和开发者应诚实行事并尊重他人权利。
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