IGCSE CCEA Computer Science: Last-Minute Revision Notes | IGCSE CCEA 计算机：考前冲刺笔记

📚 IGCSE CCEA Computer Science: Last-Minute Revision Notes | IGCSE CCEA 计算机：考前冲刺笔记

This guide covers the essential topics for the CCEA IGCSE Computer Science examination. It is designed for rapid review, helping you consolidate key concepts and avoid common pitfalls just before the exam.

本指南涵盖了 CCEA IGCSE 计算机科学考试的基本主题。它专为快速复习而设计，帮助你在考前巩固关键概念并避免常见错误。

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1. Data Representation | 数据表示

All data inside a computer is stored as binary digits (bits), where 1 represents ‘on’ and 0 represents ‘off’. The smallest addressable unit is a byte, typically 8 bits.

计算机内部的所有数据都以二进制数字（位）的形式存储，1 表示“开”，0 表示“关”。最小的可寻址单位是字节，通常为 8 位。

To convert from binary to denary, add the place values (1, 2, 4, 8, 16, …) where a 1 appears. For example, binary 1101₂ = 8 + 4 + 1 = 13₁₀.

将二进制转换为十进制时，将出现 1 的位值（1、2、4、8、16 ……）相加。例如，二进制 1101₂ = 8 + 4 + 1 = 13₁₀。

Hexadecimal (base 16) uses digits 0–9 and letters A–F. One hex digit represents four bits (a nibble), making it compact for representing memory addresses and colour codes.

十六进制（基数为 16）使用数字 0–9 和字母 A–F。一位十六进制数字表示四个位（一个半字节），因此可以紧凑地表示内存地址和颜色代码。

Binary addition follows the same principles as denary addition, with carries when the sum exceeds 1. An overflow error occurs when the result is too large for the allocated number of bits.

二进制加法遵循与十进制加法相同的规则，当和超过 1 时会产生进位。当结果过大超出分配的位数时，会发生溢出错误。

Negative integers are commonly stored using two’s complement. The most significant bit becomes a negative place value, allowing straightforward arithmetic with the same circuitry.

负整数通常使用二进制补码存储。最高有效位成为负位值，从而允许使用相同的电路直接进行算术运算。

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2. Hardware | 硬件

The central processing unit (CPU) executes instructions using the fetch-decode-execute cycle. Key components include the control unit, arithmetic logic unit (ALU), and registers such as the program counter and accumulator.

中央处理器 (CPU) 使用“取指-解码-执行”周期来执行指令。关键组件包括控制单元、算术逻辑单元 (ALU) 以及程序计数器和累加器等寄存器。

Von Neumann architecture stores both data and instructions in the same memory, while Harvard architecture uses separate memory spaces. Most personal computers follow Von Neumann design.

冯·诺依曼体系结构将数据和指令存储在同一内存中，而哈佛体系结构使用独立的内存空间。大多数个人计算机遵循冯·诺依曼设计。

Primary memory (RAM and ROM) is directly accessed by the CPU. RAM is volatile and holds currently running programs, while ROM is non-volatile and contains firmware such as the BIOS.

主存储器（RAM 和 ROM）由 CPU 直接访问。RAM 是易失性的，保存当前运行的程序；而 ROM 是非易失性的，包含固件（如 BIOS）。

Secondary storage, such as magnetic hard disks, solid-state drives, and optical media, provides non-volatile long-term storage. Factors like capacity, speed, portability, and cost influence the choice.

辅助存储器，如磁性硬盘、固态驱动器和光学介质，提供非易失性的长期存储。容量、速度、便携性和成本等因素会影响选择。

Input and output devices allow interaction with the computer. Sensors, keyboards, and microphones are typical inputs, while actuators, monitors, and speakers serve as outputs.

输入和输出设备允许与计算机交互。传感器、键盘和麦克风是典型的输入设备，而执行器、显示器和扬声器则用作输出设备。

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3. Software | 软件

System software manages hardware and provides a platform for application software. The operating system handles memory management, multitasking, file systems, and user interfaces.

系统软件管理硬件并为应用软件提供平台。操作系统处理内存管理、多任务处理、文件系统和用户界面。

Utility programs perform maintenance tasks: disk defragmentation reorganises files for faster access, encryption secures data, and compression reduces file sizes for storage and transmission.

实用程序执行维护任务：磁盘碎片整理重新组织文件以加快访问速度，加密保护数据安全，压缩可减小文件大小以便存储和传输。

Translators convert source code into machine code. A compiler translates the whole program at once, producing an executable, while an interpreter translates and executes line by line.

翻译器将源代码转换为机器码。编译器一次翻译整个程序并生成可执行文件，而解释器则逐行翻译并执行。

Application software lets users perform specific tasks. Examples include word processors, spreadsheets, databases, and web browsers. Custom-written software is created for particular needs.

应用软件让用户执行特定任务。示例包括文字处理软件、电子表格、数据库和网页浏览器。定制软件则是为特定需求而编写的。

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4. Networks | 网络

A network connects two or more computers to share resources and data. LANs cover small geographical areas, while WANs connect devices over large distances, often using the internet.

网络连接两台或更多计算机以共享资源和数据。LAN 覆盖较小的地理区域，而 WAN 则通过互联网长距离连接设备。

Common topologies include star, where all nodes connect to a central switch, and mesh, where each node may connect to several others. Star is easy to manage, but the central device is a single point of failure.

常见的拓扑结构包括星型（所有节点连接到中央交换机）和网状（每个节点可连接到多个其他节点）。星型易于管理，但中央设备是单点故障。

Protocols are sets of rules governing communication. Ethernet handles wired transmissions, Wi-Fi enables wireless connectivity, TCP/IP breaks messages into packets and ensures reliable delivery.

协议是管理通信的规则集。以太网处理有线传输，Wi-Fi 实现无线连接，TCP/IP 将消息拆分为数据包并确保可靠交付。

The Domain Name System (DNS) translates human-readable domain names into IP addresses. A MAC address uniquely identifies a network interface card, while an IP address identifies a device on a TCP/IP network.

域名系统 (DNS) 将人类可读的域名转换为 IP 地址。MAC 地址唯一标识网络接口卡，而 IP 地址标识 TCP/IP 网络上的设备。

Client-server networks have dedicated servers providing resources, while peer-to-peer networks share resources directly between machines. Cloud computing delivers services over the internet on demand.

客户端-服务器网络有专用服务器提供资源，而点对点网络在机器之间直接共享资源。云计算通过互联网按需提供服务。

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5. Cybersecurity | 网络安全

Malware is malicious software including viruses, worms, trojans, and ransomware. It can corrupt files, steal data, or hold systems hostage. Firewalls and anti-malware tools are primary defences.

恶意软件是包括病毒、蠕虫、特洛伊木马和勒索软件在内的恶意软件。它会损坏文件、窃取数据或劫持系统。防火墙和反恶意软件工具是主要的防御措施。

Social engineering attacks, such as phishing, trick users into revealing confidential information. Always verify the sender’s identity and avoid clicking suspicious links.

社会工程攻击，如网络钓鱼，诱骗用户泄露机密信息。务必验证发件人身份，避免点击可疑链接。

Encryption scrambles data so that only authorised parties with a key can read it. Caesar cipher substitutes each letter with one a fixed number of positions further in the alphabet, while modern encryption uses complex algorithms.

加密会对数据进行加扰，只有拥有密钥的授权方才能读取。凯撒密码将每个字母替换为字母表中固定位置数之后的字母，而现代加密则使用复杂算法。

Strong passwords and two-factor authentication significantly reduce unauthorised access. Penetration testing and network forensics help identify and fix vulnerabilities before attackers exploit them.

强密码和双因素认证可显著减少未授权访问。渗透测试和网络取证有助于在攻击者利用漏洞之前识别并修复漏洞。

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6. Programming Concepts | 编程概念

Variables store data values that can change during execution. Constants hold values that remain fixed. Both have a data type such as integer, real, Boolean, character, or string.

变量存储在程序执行过程中可以改变的数据值。常量保存保持固定的值。它们都有数据类型，如整数、实数、布尔、字符或字符串。

Sequence, selection, and iteration form the three basic control structures. Selection uses if-else and switch-case, while iteration employs for, while, and do-until loops.

顺序、选择和迭代构成了三种基本的控制结构。选择使用 if-else 和 switch-case，而迭代则使用 for、while 和 do-until 循环。

Subroutines (procedures and functions) allow code reuse and modular design. Functions return a value, while procedures perform actions. Parameters can be passed by value or by reference.

子程序（过程和函数）允许代码重用和模块化设计。函数返回值，而过程执行操作。参数可以通过值传递或引用传递。

Arrays are data structures that store multiple values of the same type under a single identifier. A one-dimensional list uses a single index; two-dimensional arrays use row and column indices.

数组是存储同一类型多个值的数据结构，使用单个标识符。一维列表使用单个索引；二维数组使用行索引和列索引。

String manipulation includes concatenation, sub-string extraction, and length calculation. Knowing how to convert between strings and numeric types is crucial for many practical tasks.

字符串操作包括连接、子串提取和长度计算。了解如何在字符串和数字类型之间转换对于许多实际任务至关重要。

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7. Algorithms | 算法

An algorithm is a step-by-step procedure to solve a problem. It can be expressed using flowcharts (shapes for start/end, process, decision, input/output) or pseudocode (CCEA uses a specific instruction set).

算法是解决问题的逐步过程。可以使用流程图（开始/结束、处理、判断、输入/输出等形状）或伪代码（CCEA 使用特定的指令集）来表示。

Linear search checks each element sequentially. Binary search requires a sorted list and repeatedly divides the search interval in half. Binary search is far more efficient for large datasets.

线性搜索按顺序检查每个元素。二分搜索要求列表已排序，并反复将搜索间隔减半。对于大型数据集，二分搜索的效率要高得多。

Bubble sort repeatedly swaps adjacent elements if they are out of order, causing larger items to ‘bubble’ to the end. Merge sort splits the list, recursively sorts, and then merges; it is more efficient but uses extra memory.

冒泡排序反复交换顺序错误的相邻元素，使较大的项“冒泡”到末尾。归并排序将列表拆分、递归排序然后合并；它效率更高但需要额外内存。

Efficiency of algorithms is often measured by time complexity. A linear search has O(n) complexity, while binary search has O(log n). Understanding this helps choose the best algorithm for a given context.

算法的效率通常用时间复杂度衡量。线性搜索的时间复杂度为 O(n)，二分搜索为 O(log n)。理解这一点有助于根据具体情况选择最佳算法。

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8. Databases | 数据库

A relational database organises data into tables (relations) linked by primary and foreign keys. Each table row is a record, and each column is a field with a defined data type.

关系数据库将数据组织成由主键和外键链接的表（关系）。每个表行是一条记录，每列是具有定义数据类型的字段。

Structured Query Language (SQL) is used to manage and query databases. The SELECT statement retrieves data, often with WHERE to filter, and JOIN to combine tables. For example: SELECT * FROM Students WHERE YearGroup = 11;

结构查询语言 (SQL) 用于管理和查询数据库。SELECT 语句用于检索数据，通常配合 WHERE 进行过滤，并使用 JOIN 合并表。例如：SELECT * FROM Students WHERE YearGroup = 11;

Data redundancy and inconsistency are reduced through normalisation. Ensuring each table deals with a single entity and removing partial dependencies leads to a more robust design.

通过规范化可以减少数据冗余和不一致性。确保每个表处理单一实体并消除部分依赖，可以实现更稳健的设计。

A DBMS provides security, concurrency control, and data integrity. Validation and verification rules (e.g., check digit, presence check) ensure that only sensible and accurate data enters the system.

数据库管理系统提供安全性、并发控制和数据完整性。验证与核实规则（例如校验位、存在性检查）确保只有合理且准确的数据进入系统。

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9. Ethical and Legal Issues | 伦理与法律问题

Data protection legislation, such as the GDPR and UK Data Protection Act, governs how personal data is collected, stored, and processed. Individuals have the right to access data held about them.

数据保护立法（如 GDPR 和英国《数据保护法》）规定了个人数据的收集、存储和处理方式。个人有权访问关于自己的数据。

Computer misuse laws make unauthorised access (hacking) and distribution of malware illegal. Plagiarism and copyright infringement are serious issues in the digital world; always respect intellectual property.

计算机滥用法将未经授权的访问（黑客攻击）和传播恶意软件定为非法。在数字世界中，剽窃和侵犯版权是严重问题；始终尊重知识产权。

The digital divide refers to the gap between those who have access to digital technology and the internet and those who do not. It can affect education, employment, and social inclusion.

数字鸿沟指那些能够使用数字技术和互联网的人与那些不能使用的人之间的差距。它可能影响教育、就业和社会包容。

Environmental concerns include the energy consumption of data centres and the disposal of e-waste. Sustainable computing practices, such as virtualisation and recycling, help mitigate these effects.

环境问题包括数据中心的能源消耗和电子垃圾的处理。虚拟化和回收等可持续计算实践有助于减轻这些影响。

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10. Exam Tips | 考前提示

Read each question carefully, identifying command words such as ‘describe’, ‘explain’, ‘compare’, and ‘evaluate’. Tailor your answer to the marks available; a one-line answer will rarely earn full marks for a 4-mark question.

仔细阅读每个问题，识别诸如“描述”、“解释”、“比较”和“评估”等命令词。根据可得分值调整答案；一行答案很难在 4 分题中获得满分。

For coding questions, write cleanly and indent consistently. CCEA may provide algorithm questions in pseudocode or a specific assembly-like language; ensure you can trace code manually and understand the effect of each instruction.

对于编程题，书写要整洁，缩进要一致。CCEA 可能以伪代码或特定的汇编式语言给出算法题；确保你能手动追踪代码并理解每条指令的作用。

Use technical terminology accurately. For example, say ‘primary storage is volatile’ rather than ‘memory disappears when turned off’. Precise language demonstrates thorough understanding.

准确使用技术术语。例如，说“主存储器是易失性的”而不是“关机后内存消失”。精确的语言显示出透彻的理解。

Manage your time: allocate roughly one minute per mark, and leave a few minutes at the end to review. If stuck on a question, move on and return later—do not sacrifice the rest of the paper.

管理好时间：大约每分值分配一分钟，最后留出几分钟检查。如果卡在某道题上，先跳过，稍后再回来——不要牺牲试卷的其他部分。

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