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IGCSE CCEA Computer Science: End-of-Term Revision Guide | IGCSE CCEA 计算机：期末复习提纲

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📚 IGCSE CCEA Computer Science: End-of-Term Revision Guide | IGCSE CCEA 计算机：期末复习提纲

This revision guide distils the entire IGCSE CCEA Computer Science syllabus into clear, bite-sized points. Work through each section, test yourself on the key concepts, and use the bilingual explanations to strengthen your technical vocabulary in both English and Chinese.

这份复习提纲将 IGCSE CCEA 计算机科学全部考纲浓缩成清晰的要点。逐节学习、自测关键概念，并使用中英双语解释巩固你的专业术语。

1. Data Representation | 数据表示

All data inside a computer is stored as binary digits (bits). A bit is a single 0 or 1, and 8 bits make a byte. Numbers, text, images and sound are all represented using binary patterns.

计算机内所有数据都以二进制数字（位）存储。一个位是一个 0 或 1，8 个位组成一个字节。数字、文本、图像和声音都使用二进制模式表示。

Denary (base-10) numbers can be converted to binary (base-2) and hexadecimal (base-16). For example, denary 202 is 11001010 in binary and CA in hexadecimal.

十进制数可以转换成二进制和十六进制。例如，十进制 202 的二进制是 11001010，十六进制是 CA。

Binary addition follows simple rules: 0+0=0, 0+1=1, 1+0=1, 1+1=0 carry 1, and 1+1+carry=1 carry 1. Overflow occurs when the result exceeds the available number of bits.

二进制加法遵循简单规则：0+0=0，0+1=1，1+0=1，1+1=0 进位 1，1+1+进位=1 进位 1。当结果超出可用位数时发生溢出。

Negative numbers are represented using two’s complement. To get the two’s complement of a binary number, invert all bits and add 1. This allows subtraction to be performed by adding a negative number.

负数使用二进制补码表示。将一个二进制数的所有位取反后加 1 即得到其补码。这使得可以通过加负数来执行减法。

Characters are encoded using standards such as ASCII (7-bit, 128 characters) and Unicode (up to 32 bits per character, covering global scripts). ASCII uses 1 byte per character; Unicode may use multiple bytes.

字符使用 ASCII（7 位，128 个字符）和 Unicode（每字符最多 32 位，覆盖全球文字）等标准编码。ASCII 每字符 1 字节；Unicode 可能使用多字节。

Images are stored as bitmap grids of pixels, each pixel assigned a binary colour code. Higher colour depth (bits per pixel) gives more colours; higher resolution (more pixels) gives sharper images but larger file size.

图像存储为像素点阵，每个像素分配一个二进制颜色码。更高的颜色深度（每像素位数）产生更多颜色；更高的分辨率（更多像素）使图像更清晰但文件更大。

Sound is sampled at regular intervals; each sample is a binary number representing amplitude. Sample rate (Hz) and bit depth determine quality and file size. Higher sample rate and bit depth produce higher fidelity.

声音以固定间隔采样；每个样本是代表振幅的二进制数。采样率（Hz）和位深度决定质量和文件大小。更高的采样率和位深度产生更高保真度。

2. Computer Architecture | 计算机体系结构

The central processing unit (CPU) follows the fetch–decode–execute cycle. The control unit (CU) manages execution, the arithmetic logic unit (ALU) performs calculations and logic operations, and registers provide fast temporary storage.

中央处理器遵循取指–解码–执行周期。控制单元管理执行，算术逻辑单元执行计算和逻辑操作，寄存器提供快速临时存储。

Key registers include the program counter (PC), memory address register (MAR), memory data register (MDR), current instruction register (CIR) and accumulator (ACC). The PC holds the address of the next instruction.

重要寄存器包括程序计数器（PC）、内存地址寄存器（MAR）、内存数据寄存器（MDR）、当前指令寄存器（CIR）和累加器（ACC）。PC 存放下一条指令的地址。

The von Neumann architecture stores both data and instructions in the same memory. This allows programs to be changed easily, but means the CPU must share the same bus for instructions and data (the von Neumann bottleneck).

冯·诺依曼结构将数据和指令存储在同一内存中。这使得程序易于修改，但意味着 CPU 必须通过同一条总线传输指令和数据（冯·诺依曼瓶颈）。

Factors affecting CPU performance: clock speed (GHz), number of cores, and cache size. A higher clock speed means more cycles per second. Multiple cores allow parallel processing. Cache stores frequently accessed instructions/data close to the CPU.

影响 CPU 性能的因素：时钟速度（GHz）、核心数量和缓存大小。更高的时钟速度意味着每秒更多周期。多核允许并行处理。缓存将频繁访问的指令/数据存储在靠近 CPU 的地方。

Embedded systems are dedicated computers built into larger devices (e.g. washing machines, digital watches). They typically have a microcontroller, low power consumption, and ROM to store firmware.

嵌入式系统是内嵌在大型设备中的专用计算机（如洗衣机、电子手表）。它们通常包含微控制器，功耗低，并使用 ROM 存储固件。

3. Input and Output Devices | 输入输出设备

Input devices feed data into a computer. Common examples: keyboard, mouse, touchscreen, microphone, scanner, barcode reader, sensor (temperature, light, motion). Sensors convert physical quantities into digital signals.

输入设备将数据馈入计算机。常见的例子：键盘、鼠标、触摸屏、麦克风、扫描仪、条形码阅读器、传感器（温度、光线、运动）。传感器将物理量转换成数字信号。

A 2D scanner captures a flat image by reflecting light off the document; a 3D scanner uses lasers or structured light to capture the shape of an object. Barcode readers use laser or LED light to read parallel lines representing numbers.

二维扫描仪通过文档反射光线捕获平面图像；三维扫描仪使用激光或结构光捕获物体外形。条形码阅读器使用激光或 LED 光线读取代表数字的平行线。

Output devices present information from the computer. Examples: monitor (LCD/LED), printer (inkjet, laser, 3D), speakers, projector. Printers differ in speed, cost per page, and quality – laser printers use toner and are fast for text; inkjet printers are better for colour images.

输出设备呈现计算机的信息。例如：显示器（LCD/LED）、打印机（喷墨、激光、3D）、扬声器、投影仪。打印机在速度、单页成本和打印质量上有差异——激光打印机使用碳粉，打印文本速度快；喷墨打印机更适合彩色图像。

3D printers build objects layer by layer using materials such as PLA or resin. They are used in rapid prototyping, medical implants and manufacturing.

3D 打印机使用 PLA 或树脂等材料逐层构建物体。它们用于快速原型制作、医疗植入物和制造业。

Touchscreens are both input and output devices. Capacitive screens detect the electrical charge of a finger; resistive screens respond to pressure. Infrared and optical touchscreens use light beams.

触摸屏既是输入又是输出设备。电容屏检测手指的电荷；电阻屏响应压力。红外和光学触摸屏使用光束。

4. Storage | 存储器

Storage devices hold data permanently (non-volatile). Primary storage is RAM (volatile) and ROM (non-volatile). RAM holds currently running programs and data; ROM contains the boot program (firmware).

存储设备永久保存数据（非易失性）。主存储器是 RAM（易失性）和 ROM（非易失性）。RAM 保存当前运行的程序和数据；ROM 包含启动程序（固件）。

Secondary storage includes magnetic (hard disk drive, HDD), solid-state (SSD, USB flash drive), and optical (CD, DVD, Blu-ray). HDDs have spinning platters and mechanical heads; SSDs use NAND flash chips with no moving parts – faster, more durable, but usually more expensive per GB.

辅助存储包括磁性（硬盘驱动器 HDD）、固态（SSD、USB 闪存盘）和光学（CD、DVD、蓝光）。HDD 具有旋转盘片和机械读写头；SSD 使用 NAND 闪存芯片，无移动部件——更快、更耐用，但通常每 GB 更贵。

Optical discs store data as pits and lands read by a laser. CDs hold ~700 MB, DVDs ~4.7 GB, Blu-rays ~25 GB. They are portable and cheap but have slower access times and are prone to scratches.

光盘以凹坑和平面存储数据，由激光读取。CD 约 700 MB，DVD 约 4.7 GB，蓝光约 25 GB。它们便携、便宜，但访问速度较慢且易划伤。

Cloud storage stores data on remote servers accessed via the internet. Advantages: accessibility from anywhere, automatic backup, scalable capacity. Disadvantages: requires internet connection, ongoing subscription costs, potential security risks.

云存储将数据存储在通过互联网访问的远程服务器上。优点：可从任何地方访问、自动备份、可扩展容量。缺点：需要网络连接、持续订阅费用、潜在安全风险。

Capacity units: bit, byte (B), kilobyte (KB, 10³ bytes or 2¹⁰ bytes, depending on context), megabyte (MB), gigabyte (GB), terabyte (TB). Data transfer speeds are measured in bits per second (bps).

容量单位：位、字节（B）、千字节（KB，10³ B 或 2¹⁰ B，视上下文而定）、兆字节（MB）、吉字节（GB）、太字节（TB）。数据传输速度以每秒位数（bps）度量。

5. Software | 软件

System software manages hardware and provides a platform for application software. The operating system (OS) handles memory management, multitasking, file management, user interface, peripheral management and security.

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、文件管理、用户界面、外设管理和安全。

Utility software performs maintenance tasks: antivirus, firewall, disk defragmentation, backup, compression, file repair. Antivirus scans for and removes malware using signature databases and heuristic analysis.

实用软件执行维护任务：防病毒、防火墙、磁盘碎片整理、备份、压缩、文件修复。防病毒软件使用特征库和启发式分析扫描并清除恶意软件。

Application software helps users perform specific tasks. Examples: word processor, spreadsheet, database, web browser, graphics editor. Spreadsheets can model data using formulas, functions (SUM, AVERAGE, IF) and charts.

应用软件帮助用户执行特定任务。例如：文字处理器、电子表格、数据库、网页浏览器、图形编辑器。电子表格可以使用公式、函数（SUM, AVERAGE, IF）和图表对数据建模。

Open-source software is distributed with its source code, allowing users to study, modify and share it (e.g. Linux, LibreOffice). Proprietary software restricts access to source code and typically requires a paid licence (e.g. Microsoft Windows, Adobe Photoshop).

开源软件连同源代码一起分发，允许用户学习、修改和分享它（如 Linux、LibreOffice）。专有软件限制对源代码的访问，通常需要付费许可证（如 Microsoft Windows、Adobe Photoshop）。

6. Networks | 网络

A network connects devices to share resources and communicate. LAN (Local Area Network) covers a small geographical area, usually a building; WAN (Wide Area Network) connects LANs across cities or countries. The internet is the largest WAN.

网络连接设备以共享资源和通信。LAN（局域网）覆盖小地理区域，通常是一栋建筑；WAN（广域网）跨城市或国家连接 LAN。互联网是最大的 WAN。

Network hardware: switch (connects devices in a LAN, forwarding frames based on MAC addresses), router (connects different networks, forwarding packets based on IP addresses), modem (converts digital signals to analogue for transmission over telephone/cable lines), wireless access point (connects Wi-Fi devices).

网络硬件：交换机（在 LAN 中连接设备，基于 MAC 地址转发帧）、路由器（连接不同网络，基于 IP 地址转发数据包）、调制解调器（将数字信号转换为模拟信号通过电话/电缆线传输）、无线接入点（连接 Wi-Fi 设备）。

Network topologies: star (all devices connect to a central switch/node; easy to add/remove devices, but central node is single point of failure), mesh (devices connect to many others; more reliable, but expensive to cable), bus (single backbone cable; simple but performance degrades with more devices).

网络拓扑：星型（所有设备连接到中央交换机/节点；易增删设备，但中央节点是单点故障）、网状（设备连接多个其他设备；更可靠，但布线昂贵）、总线型（单根骨干电缆；简单但设备增多时性能下降）。

Protocols: TCP/IP (Transmission Control Protocol / Internet Protocol) provides reliable data delivery using packets. HTTP/HTTPS governs web page transfer; FTP transfers files; SMTP and POP3/IMAP handle email sending and receiving. Wi-Fi uses IEEE 802.11 standards.

协议：TCP/IP（传输控制协议/互联网协议）使用数据包提供可靠的数据传输。HTTP/HTTPS 管理网页传输；FTP 传输文件；SMTP 和 POP3/IMAP 处理电子邮件的发送和接收。Wi-Fi 使用 IEEE 802.11 标准。

IP addresses (IPv4, 32-bit; IPv6, 128-bit) uniquely identify devices on a network. MAC addresses are hardware addresses burnt into the NIC. DNS (Domain Name System) translates domain names (e.g. aleveler.com) to IP addresses.

IP 地址（IPv4 32 位；IPv6 128 位）唯一标识网络上的设备。MAC 地址是固化在网卡中的硬件地址。DNS（域名系统）将域名（如 aleveler.com）解析为 IP 地址。

7. Network Security | 网络安全

Threats: malware (virus, worm, Trojan horse), phishing, denial-of-service (DoS) attacks, SQL injection, brute-force attacks. Social engineering tricks users into revealing passwords or sensitive information.

威胁：恶意软件（病毒、蠕虫、特洛伊木马）、网络钓鱼、拒绝服务攻击、SQL 注入、暴力破解攻击。社会工程学诱骗用户泄露密码或敏感信息。

Encryption scrambles data so only authorised parties with the key can read it. Symmetric encryption uses the same key for encryption and decryption; asymmetric (public-key) encryption uses a public key to encrypt and a private key to decrypt.

加密将数据打乱，只有持有密钥的授权方才能读取。对称加密使用相同密钥进行加密和解密；非对称（公钥）加密使用公钥加密、私钥解密。

Authentication methods: passwords (should be strong, containing mixed characters), biometrics (fingerprint, iris, face recognition), two-factor authentication (2FA) – combining something you know (password) with something you have (phone) or something you are (biometric).

身份验证方法：密码（应足够强，包含混合字符）、生物特征（指纹、虹膜、面部识别）、双因素认证（2FA）——结合你知道的（密码）和你拥有的（手机）或你是什么（生物特征）。

Firewalls filter incoming and outgoing network traffic based on predefined security rules. They can block unauthorised access and log suspicious activity. Antivirus software detects and removes malware; it must be updated regularly to recognise new threats.

防火墙基于预定义安全规则过滤进出网络流量。它们可阻止未经授权的访问并记录可疑活动。防病毒软件检测并删除恶意软件；必须定期更新以识别新威胁。

Data security measures: access levels (read, write, delete permissions), physical security (locks, surveillance), regular backups (full, incremental), offsite storage and disaster recovery plans.

数据安全措施：访问级别（读取、写入、删除权限）、物理安全（门锁、监控）、定期备份（完整、增量）、异地存储和灾难恢复计划。

8. Databases | 数据库

A database is an organised collection of data. In a relational database, data is stored in tables (relations) linked by primary keys and foreign keys. Each table consists of records (rows) and fields (columns).

数据库是有组织的数据集合。在关系数据库中，数据存储在由主键和外键链接的表（关系）中。每个表由记录（行）和字段（列）组成。

A primary key uniquely identifies each record in a table (e.g. StudentID). A foreign key in one table refers to the primary key in another, creating a relationship (e.g. linking Orders to Customers).

主键唯一标识表中的每条记录（如 StudentID）。一个表中的外键引用另一表的主键，建立关系（如将 Orders 链接到 Customers）。

Data types: text/string (alphanumeric), integer (whole number), real/float (decimal), Boolean (true/false), date/time. Choosing appropriate data types saves storage and maintains data integrity.

数据类型：文本/字符串（字母数字）、整数、浮点数（小数）、布尔型（真/假）、日期/时间。选择合适的数据类型可以节省存储并保持数据完整性。

SQL (Structured Query Language) is used to query and manipulate databases. Basic commands: SELECT FROM

WHERE ; INSERT INTO

VALUES (…); UPDATE

SET = WHERE ; DELETE FROM

WHERE .

SQL（结构化查询语言）用于查询和操作数据库。基本命令：SELECT <字段> FROM <表> WHERE <条件>；INSERT INTO <表> VALUES (…)；UPDATE <表> SET <字段>=<值> WHERE <条件>；DELETE FROM <表> WHERE <条件>。

Data redundancy is minimised through normalisation, which organises fields into related tables to reduce duplicate data. A flat file database stores all data in a single table and often suffers from redundancy.

通过规范化减少数据冗余，它将字段组织到相关表中以减少重复数据。平面文件数据库将所有数据存储在单表中，通常存在冗余问题。

9. Programming Concepts | 编程概念

Sequence, selection and iteration are the three fundamental programming constructs. Sequence executes instructions in order. Selection uses IF…THEN…ELSE or CASE statements to make decisions. Iteration repeats code using FOR loops (count-controlled), WHILE loops (condition-controlled) or REPEAT…UNTIL loops.

顺序、选择和迭代是三个基本编程结构。顺序按次序执行指令。选择使用 IF…THEN…ELSE 或 CASE 语句做决策。迭代使用 FOR 循环（计数控制）、WHILE 循环（条件控制）或 REPEAT…UNTIL 循环重复代码。

Variables store data that can change during program execution. Each variable has a data type: integer, real, Boolean, char, string. Constants hold values that do not change. Arrays are data structures that store multiple items of the same type under one identifier, accessed by index (e.g. array[0]).

变量存储程序执行期间可以改变的数据。每个变量有一个数据类型：整数、浮点数、布尔、字符、字符串。常量保存不变的值。数组是将同一类型多项数据存储在一个标识符下的数据结构，通过索引访问（如 array[0]）。

Subprograms divide a large program into manageable pieces. Procedures carry out tasks but do not return a value; functions perform tasks and return a value. Parameters pass data into subprograms (by value or by reference).

子程序将大程序分成可管理的片段。过程执行任务但不返回值；函数执行任务并返回值。参数将数据传入子程序（按值传递或按引用传递）。

String manipulation: length, substring, concatenation (joining), case conversion (UPPER, lower), character extraction. Basic file handling: open, read, write, close. Data can be read from and written to text files using pseudocode.

字符串操作：长度、子串、拼接（连接）、大小写转换（UPPER、lower）、字符提取。基本文件处理：打开、读取、写入、关闭。可使用伪代码从文本文件读取数据并写入数据。

Testing and debugging: syntax errors break language rules (e.g. missing colon), logic errors produce unexpected results, runtime errors occur during execution (e.g. division by zero). Test plans use normal, boundary and erroneous data.

测试与调试：语法错误违反语言规则（如缺少冒号），逻辑错误产生非预期结果，运行时错误在执行时发生（如除以零）。测试计划使用正常数据、边界数据和错误数据。

10. Algorithms and Pseudocode | 算法与伪代码

An algorithm is a step-by-step solution to a problem. Algorithms can be expressed using flowcharts or pseudocode. Pseudocode uses clear, structured English-like statements: SET, INPUT, OUTPUT, WHILE, IF, FOR, etc.

算法是解决问题的逐步解决方案。算法可以用流程图或伪代码表示。伪代码使用清晰、结构化的类英语语句：SET、INPUT、OUTPUT、WHILE、IF、FOR 等。

Standard searching algorithms: linear search checks each item one by one until a match is found; works on unsorted lists but can be slow. Binary search requires a sorted list, repeatedly dividing the search interval in half. Binary search is more efficient for large lists (O(log n) vs O(n)).

标准搜索算法：线性搜索逐个检查每一项直到找到匹配项；适用于未排序列表但速度可能较慢。二分搜索要求列表已排序，反复将搜索区间分为两半。二分搜索对于大列表更高效（O(log n) 对 O(n)）。

Sorting algorithms: bubble sort compares adjacent items and swaps them if they are in the wrong order, repeating until no swaps are needed. Insertion sort builds a sorted portion by inserting each new element into the correct place. Merge sort uses a divide-and-conquer approach, splitting the list into halves recursively and merging sorted halves.

排序算法：冒泡排序比较相邻项，若顺序错误则交换，重复直到无交换。插入排序通过将每个新元素插入正确位置来构建已排序部分。归并排序采用分治法，递归地将列表分成两半然后合并已排序的半部分。

Algorithm efficiency can be measured by time complexity. Common complexities: constant O(1), linear O(n), logarithmic O(log n), quadratic O(n²). Knowing complexity helps choose the right algorithm for large data sets.

算法效率可用时间复杂度衡量。常见复杂度：常数 O(1)、线性 O(n)、对数 O(log n)、平方 O(n²)。了解复杂度有助于为大数据集选择合适的算法。

Trace tables are used to manually step through an algorithm and record variable values at each step. This is essential for finding logic errors and understanding how the algorithm works.

跟踪表用于手动逐步执行算法，并记录每一步的变量值。这对发现逻辑错误和理解算法如何工作至关重要。

11. Data Validation and Verification | 数据验证与核实

Validation checks that data is reasonable and within acceptable limits before processing. Types: range check (e.g. age between 0 and 120), type check (is it an integer?), length check, presence check (field not empty), format check (pattern like AB123), check digit (extra digit calculated from others, e.g. ISBN-13, barcodes).

验证在处理前检查数据是否合理且在可接受范围内。类型：范围检查（如年龄在 0 到 120 之间）、类型检查（是否为整数？）、长度检查、存在检查（字段非空）、格式检查（模式如 AB123）、校验位（根据其他位计算的额外位，如 ISBN-13、条形码）。

Verification is the process of ensuring data entered matches the original source. Double entry (typing twice) compares the two versions; visual check compares on-screen or printed data with the original document; proofreading involves someone reading for errors.

核实是确保输入数据与原始源匹合的过程。双录（键入两次）比较两个版本；目视检查将屏幕或打印数据与原始文档比较；校对由人阅读查找错误。

Validation cannot guarantee data is correct; it only checks it is plausible. For example, an age of 25 is valid but could still be typed wrongly as 35. Both validation and verification are needed for reliable data.

验证不能保证数据正确；它只检查合理程度。例如，年龄 25 是有效的，但仍可能误打为 35。为了数据可靠，验证与核实皆不可少。

Check digits: the most common is the modulo-11 algorithm. For ISBN-10, each digit is multiplied by its position weight, summed, and the remainder after division by 11 gives the check digit (10 represented as X). The latest ISBN-13 uses modulo-10 with alternating weights 1 and 3.

校验位：最常见的是模 11 算法。对于 ISBN-10，每位乘以其位置权重，求和，除以 11 的余数即校验位（10 表示为 X）。最新 ISBN-13 使用模 10，交替权重 1 和 3。

12. Ethical, Legal and Environmental Issues | 伦理、法律与环境议题

Computing raises ethical concerns: digital divide, cyberbullying, online privacy, misinformation, and screen addiction. Professionals should follow codes of conduct promoting fairness and respect.

计算引发伦理关注：数字鸿沟、网络欺凌、在线隐私、虚假信息和屏幕成瘾。专业人员应遵循倡导公平与尊重的行为准则。

Legal frameworks: the Data Protection Act (or GDPR) governs how personal data is collected, stored and used, giving individuals rights over their data. The Computer Misuse Act makes unauthorised access to computer systems (hacking) and malware creation illegal.

法律框架：数据保护法（或 GDPR）规范个人数据的收集、存储和使用，赋予个人对其数据的权利。计算机滥用法将未经授权访问计算机系统（黑客攻击）和制作恶意软件定为非法。

The Copyright, Designs and Patents Act protects intellectual property, covering software licences, digital media and online content. Plagiarism is using someone else’s work without permission or attribution.

版权、设计与专利法保护知识产权，涵盖软件许可、数字媒体和在线内容。剽窃是未经许可或引用而使用他人作品。

Environmental impact: e-waste (discarded electronic devices) contains toxic materials and must be recycled responsibly. Data centres consume huge amounts of electricity for servers and cooling, contributing to carbon emissions. Green computing promotes energy-efficient hardware, virtualisation, sleep modes and responsible disposal.

环境影响：电子垃圾（废弃电子设备）含有毒材料，必须负责任地回收。数据中心消耗大量电力用于服务器和冷却，增加碳排放。绿色计算倡导节能硬件、虚拟化、休眠模式和负责任处置。

The digital divide is the gap between those who have access to technology and the internet and those who do not. It can be caused by economic, geographical or social factors, and limits education and job opportunities.

数字鸿沟是指能够接触技术与互联网的人与不能接触者之间的差距。它可能由经济、地理或社会因素造成，并限制教育与就业机会。

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