📚 GCSE WJEC Computer Science: Last-Minute Revision Notes | GCSE WJEC 计算机：考前冲刺笔记
This set of revision notes is designed to help you quickly refresh the core topics for the GCSE WJEC Computer Science examination. It condenses key concepts into short, paired English–Chinese explanations, so you can scan through the essentials in one sitting. Focus on the terminology, logic, and the way components interact—these are the building blocks of every exam question.
本套冲刺笔记旨在帮助你快速回顾 GCSE WJEC 计算机科学考试的核心主题。它将关键概念浓缩为简短的英中对照讲解，你可以在一次复习中浏览所有要点。请重点关注术语、逻辑以及各组件之间的相互作用——这些正是每道考题的基础。
1. System Architecture: Von Neumann and the CPU | 系统架构：冯·诺依曼与中央处理器
The vast majority of modern computers follow the Von Neumann architecture, where both instructions and data are stored in the same memory unit. The Central Processing Unit (CPU) consists of the Control Unit (CU) which directs operations, the Arithmetic Logic Unit (ALU) which performs calculations and logical comparisons, and registers such as the Program Counter (PC), Memory Address Register (MAR), and Memory Data Register (MDR). The fetch–decode–execute cycle repeats billions of times per second: the CPU fetches an instruction from RAM, decodes it in the CU, and then executes it, often storing the result back in a register or memory.
绝大多数现代计算机遵循冯·诺依曼体系结构，指令和数据存放在同一个存储器中。中央处理器（CPU）包含负责指挥操作的控制单元（CU）、执行算术与逻辑运算的算术逻辑单元（ALU），以及程序计数器（PC）、内存地址寄存器（MAR）和内存数据寄存器（MDR）等寄存器。取指–译码–执行周期每秒重复数十亿次：CPU 从 RAM 中取出指令，在 CU 中译码，然后执行，通常将结果存回寄存器或内存。
2. Memory and Storage | 内存与存储
Primary memory includes volatile RAM (Random Access Memory) which temporarily holds running programs and data, and non-volatile ROM (Read-Only Memory) that stores the boot firmware. Secondary storage is permanent and is needed to store the operating system, applications, and user files when the power is off. Common storage types are magnetic hard disk drives (HDD), solid-state drives (SSD) which are faster and more durable with no moving parts, and optical discs like CDs and DVDs. Cloud storage offers remote access but depends on internet connectivity and raises security concerns.
主存储器包括易失性的 RAM（随机存取存储器），暂时存放正在运行的程序和数据；以及非易失性的 ROM（只读存储器），用于存储启动固件。辅助存储器是永久性的，用于在电源关闭时保存操作系统、应用程序和用户文件。常见存储类型有磁性硬盘驱动器（HDD）、没有活动部件因而速度更快且更耐用的固态硬盘（SSD），以及 CD 和 DVD 等光盘。云存储支持远程访问，但依赖网络连接，并引发安全问题。
Units: A bit is a single binary digit 0 or 1. 1 nibble = 4 bits, 1 byte = 8 bits. 1 KB = 1024 bytes, 1 MB ≈ 1 million bytes, 1 GB ≈ 1 billion bytes, 1 TB ≈ 1 trillion bytes.
单位：一位（bit）是单个二进制数字 0 或 1。1 个半字节（nibble）= 4 位，1 字节（byte）= 8 位。1 KB = 1024 字节，1 MB ≈ 一百万字节，1 GB ≈ 十亿字节，1 TB ≈ 一万亿字节。
3. Networks and Topologies | 网络与拓扑
Networks can be classified by geographical scope: a LAN (Local Area Network) covers a small area like a school or office, while a WAN (Wide Area Network) connects LANs over large distances such as cities or countries. Topologies define the layout. In a star topology, all devices connect to a central switch or hub in a star topology; if one cable fails, only that device is affected, but the central device is a single point of failure. A mesh topology provides multiple paths between nodes for high reliability. The Internet uses protocols like TCP/IP to enable global communication, and data is broken into packets, each with source and destination addresses.
网络可按地理范围分类：LAN（局域网）覆盖学校或办公室等小范围区域，而 WAN（广域网）将各局域网跨城市或国家连接起来。拓扑结构定义布局。在星型拓扑中，所有设备都与中心交换机或集线器相连；某条线缆故障只影响该设备，但中心设备是单一故障点。网状拓扑在节点之间提供多条路径，可靠性高。互联网使用 TCP/IP 等协议实现全球通信，数据被分成数据包，每个包都包含源地址和目的地址。
Wired vs wireless: Ethernet uses cables for reliable, high-speed connections. Wi‑Fi uses radio waves, offering mobility but more susceptible to interference and eavesdropping. Factors affecting network performance include bandwidth (amount of data that can be transmitted per second), number of users, and transmission media.
有线与无线：以太网使用线缆提供可靠的高速连接。Wi‑Fi 使用无线电波，提供移动性，但更容易受到干扰和窃听。影响网络性能的因素包括带宽（每秒能传输的数据量）、用户数量以及传输介质。
4. Network Security | 网络安全
Common threats include malware (viruses, worms, ransomware) that can damage files or lock systems, phishing emails that deceive users into giving away passwords, brute-force attacks that try many passwords, and Denial of Service (DoS) attacks that overwhelm a server with traffic. Defensive measures include firewalls that filter incoming and outgoing traffic, encryption that scrambles data so only authorised parties can read it, and strong password policies. Penetration testing is used to identify vulnerabilities before attackers do.
常见威胁包括能破坏文件或锁定系统的恶意软件（病毒、蠕虫、勒索软件），诱骗用户交出密码的钓鱼邮件，尝试大量密码的暴力破解攻击，以及用流量淹没服务器使其瘫痪的拒绝服务（DoS）攻击。防御措施包括过滤进出流量的防火墙、将数据加扰使只有授权方才能读取的加密技术，以及强密码策略。渗透测试用于在攻击者之前发现漏洞。
Social engineering exploits human psychology rather than technical flaws. For example, ‘shoulder surfing’ involves watching someone type their password. Organisations enforce security policies and regularly update software to patch known vulnerabilities.
社会工程学利用人的心理而非技术缺陷。例如，“肩窥”就是偷看他人输入密码。组织通过实施安全策略并定期更新软件来修补已知漏洞。
5. System Software and Operating Systems | 系统软件与操作系统
The operating system (OS) manages hardware resources, provides a user interface (GUI or command line), handles file management, and manages memory and processes. Multitasking allows multiple programs to run concurrently by rapidly switching the CPU between tasks. Utility software carries out maintenance tasks: disk defragmentation reorganises fragmented data for faster access, compression reduces file size, and antivirus programs detect and remove malware.
操作系统（OS）管理硬件资源、提供用户界面（图形化或命令行）、处理文件管理以及管理内存和进程。多任务处理通过 CPU 在任务间快速切换，使多个程序能够并发运行。实用工具软件执行维护任务：磁盘碎片整理重新组织碎片数据以加快访问速度，压缩减小文件体积，防病毒程序检测并清除恶意软件。
The OS uses the instruction set of the CPU and sits between applications and hardware, translating high-level requests into low-level operations.
操作系统使用 CPU 的指令集，位于应用程序与硬件之间，将高级请求转换为低级操作。
6. Ethical, Legal, and Environmental Impacts | 伦理、法律与环境影响
The use of technology creates ethical dilemmas about privacy, surveillance, and the digital divide. The Data Protection Act 2018 (UK GDPR) governs how personal data can be collected, processed, and stored, giving individuals rights over their data. The Computer Misuse Act criminalises unauthorised access, modification, and malware creation. The Copyright, Designs and Patents Act protects intellectual property, including software and digital content.
技术的使用引发了关于隐私、监控和数字鸿沟的伦理难题。《2018 年数据保护法》（英国 GDPR）规定了个人数据如何被收集、处理和存储，赋予个人对其数据拥有的权利。《计算机滥用法》将未经授权的访问、修改以及恶意软件制作定为犯罪。《版权、外观设计和专利法》保护知识产权，包括软件和数字内容。
Environmental concerns focus on energy consumption of data centres, and the disposal of electronic waste (e-waste). The “Reduce, Reuse, Recycle” approach is encouraged, and the WEEE Directive aims to minimise e-waste.
环境关注点主要在于数据中心的能源消耗以及电子垃圾（e-waste）的处理。鼓励采用“减量、重用、回收”的方式，而《废弃电子电气设备指令》（WEEE）旨在减少电子垃圾。
7. Algorithms and Computational Thinking | 算法与计算思维
Computational thinking breaks a problem down into manageable parts (decomposition), identifies patterns, focuses on relevant details (abstraction), and creates step-by-step instructions (algorithm). Common algorithms include linear search (checking each item in turn) and binary search (repeatedly splitting a sorted list in half). Sorting algorithms like bubble sort repeatedly compare adjacent elements and swap them if they are in the wrong order, while merge sort divides the list and merges sorted sublists.
计算思维将问题分解为可管理的部分（分解）、识别模式、关注相关细节（抽象），并创建逐步指令（算法）。常见算法包括线性搜索（依次检查每一项）和二分搜索（反复将有序列表分成两半）。排序算法如冒泡排序反复比较相邻元素并在顺序错误时交换它们，而归并排序则将列表分割再合并已排序的子列表。
Flowcharts use standard symbols: oval for start/end, parallelogram for input/output, rectangle for process, diamond for decision. Pseudocode combines everyday language with logical structures such as IF…THEN…ELSE, FOR loops and WHILE loops.
流程图使用标准符号：椭圆形表示开始/结束，平行四边形表示输入/输出，矩形表示处理过程，菱形表示判断。伪代码将日常语言与逻辑结构相结合，如 IF…THEN…ELSE、FOR 循环和 WHILE 循环。
8. Programming Concepts | 编程概念
Variables are named memory locations holding values that can change. They have a data type: integer (whole numbers), real/float (decimal numbers), Boolean (true/false), character (single symbol), and string (sequence of characters). Constants are named values that cannot be changed. Assignment sets a variable’s value, e.g. score = 10. Selection uses if–else statements to run different code paths based on conditions. Iteration uses for loops (count-controlled) or while loops (condition-controlled).
变量是具有名称的存储位置，其值可以改变。它们具有数据类型：整型（整数）、实型/浮点型（小数）、布尔型（真/假）、字符型（单个符号）和字符串型（字符序列）。常量是值不可更改的命名数值。赋值语句设置变量的值，例如 score = 10。选择结构使用 if–else 语句根据条件执行不同的代码路径。迭代使用 for 循环（计数控制）或 while 循环（条件控制）。
Arrays (lists) store multiple values under one name, accessed by an index. Subprograms (procedures and functions) divide code into reusable blocks; functions return a value, procedures do not. File handling operations: open, read, write, close.
数组（列表）存储多个值并使用索引进行访问。子程序（过程和函数）将代码划分为可复用的模块；函数返回值，过程不返回值。文件处理操作：打开、读取、写入、关闭。
9. Data Representation | 数据表示
Computers use binary (base‑2). A denary (base‑10) number is converted to binary by repeated division by 2, recording remainders. Binary to denary uses place values. Hexadecimal (base‑16) is a shorter way to represent binary nibbles, using digits 0‑9 and letters A‑F. Character sets like ASCII use 7 or 8 bits per character; Unicode uses up to 32 bits to represent a vast range of characters from all world writing systems.
计算机使用二进制（基数为 2）。将十进制数转换为二进制数可通过反复除以 2 并记录余数来实现。二进制转十进制使用位权值。十六进制（基数为 16）是表示二进制半字节的更简短方式，使用 0‑9 以及 A‑F。如 ASCII 这样的字符集每个字符使用 7 或 8 位；Unicode 使用最多 32 位来表示全球所有书写系统中的各种字符。
Images: A bitmap image is a grid of pixels; each pixel’s colour is represented by a binary code. Colour depth (bits per pixel) determines the number of colours, e.g. 8‑bit colour depth gives 2⁸ = 256 colours. Higher resolution means more pixels → larger file size. Sound: Analogue sound is sampled at regular intervals; sample rate (Hz) and bit depth affect quality and file size.
图像：位图图像是由像素组成的网格；每个像素的颜色用二进制码表示。颜色深度（每像素位数）决定颜色数量，例如 8 位颜色深度对应 2⁸ = 256 种颜色。分辨率越高像素越多 → 文件越大。声音：模拟声音以固定间隔采样；采样率（Hz）和位深度影响音质和文件大小。
Compression reduces file size. Lossy compression (e.g., JPEG, MP3) permanently removes some data; lossless compression (e.g., ZIP, PNG) preserves all original data and restores the file exactly.
压缩可减小文件大小。有损压缩（如 JPEG、MP3）会永久删除部分数据；无损压缩（如 ZIP、PNG）保留所有原始数据并可完全还原文件。
10. Logic Gates and Truth Tables | 逻辑门与真值表
Logic gates are the building blocks of digital circuits. The fundamental gates are NOT, AND, OR. A NOT gate simply inverts its input. An AND gate outputs 1 only when all inputs are 1. An OR gate outputs 1 when at least one input is 1. Truth tables list all possible input combinations and their corresponding outputs.
逻辑门是数字电路的基本构件。基本门电路包括 NOT、AND、OR。NOT 门简单地将输入取反。AND 门仅在所有输入均为 1 时才输出 1。OR 门只要至少一个输入为 1 就输出 1。真值表列出所有可能的输入组合及其对应的输出。
| Gate | Symbol | Truth Table |
|---|---|---|
| NOT | ¬A or A’ | A=0 → 1; A=1 → 0 |
| AND | A ∧ B | 0,0→0; 0,1→0; 1,0→0; 1,1→1 |
| OR | A ∨ B | 0,0→0; 0,1→1; 1,0→1; 1,1→1 |
| XOR | A ⊕ B | 0,0→0; 0,1→1; 1,0→1; 1,1→0 |
Combining gates creates circuits that perform arithmetic, control flow, and store data. Boolean algebra can be used to simplify logical expressions, reducing the number of gates required.
组合多个门电路可构建出执行算术运算、控制流程和存储数据的电路。布尔代数可用于简化逻辑表达式，从而减少所需的门电路数量。
Published by TutorHao | Computer Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导