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

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

This concise revision guide covers every key topic for the IGCSE AQA Computer Science examination. Use it to refresh your memory on data representation, networking, algorithms, programming, and exam technique. Each section presents bite-sized facts in paired English and Chinese explanations.

这份精炼的复习指南涵盖 IGCSE AQA 计算机科学考试的所有关键主题。用它来快速回顾数据表示、网络、算法、编程和考试技巧等内容。每个小节都以中英对照的要点形式呈现，方便记忆。

1. Data Representation | 数据表示

• Binary is a base‑2 system using only digits 0 and 1. Each digit position represents a power of 2 (e.g., 2³, 2², 2¹, 2⁰).

  二进制是以 2 为基数的计数系统，只使用 0 和 1。每一位的权重是 2 的幂（例如 2³, 2², 2¹, 2⁰）。

• To convert binary to decimal, multiply each bit by its column weight and sum the results: 1010₂ = 1×2³ + 0×2² + 1×2¹ + 0×2⁰ = 10₁₀.

  将二进制转换为十进制时，用每位乘以对应权重再求和：1010₂ = 1×2³ + 0×2² + 1×2¹ + 0×2⁰ = 10₁₀。

• Hexadecimal uses base‑16 with symbols 0–9 and A–F. It is often used as a shorthand for binary because one hex digit represents exactly four bits.

  十六进制采用基数 16，使用 0–9 和 A–F 表示。因为一个十六进制位恰好对应四位二进制，所以常被用作二进制的简便写法。

• Overflow occurs when the result of a calculation is too large to fit in the fixed number of bits allocated inside the CPU.

  当一个计算结果超出了 CPU 内部分配的固定位数所能表示的最大值时，就会发生溢出。

• Character sets: standard ASCII uses 7 bits to encode 128 characters; extended ASCII uses 8 bits. Unicode uses up to 32 bits to represent characters from all writing systems.

  字符集：标准 ASCII 用 7 位编码 128 个字符；扩展 ASCII 用 8 位。Unicode 最多使用 32 位，可表示全世界所有书写系统的字符。

• Images are represented as a grid of pixels, each assigned a binary code for its colour. Resolution is the total pixel count; colour depth is the number of bits per pixel.

  图像由像素网格表示，每个像素用二进制代码记录其颜色。分辨率是像素总数，颜色深度是每个像素使用的位数。

• Sound is digitised by sampling the amplitude at regular intervals. Sample rate (Hz) and bit depth determine the quality and file size of the audio.

  声音通过等间隔采样振幅来数字化。采样率（Hz）和采样位数决定了音频的质量和文件大小。

2. Computer Architecture | 计算机体系结构

• The CPU contains the Control Unit (CU) which decodes instructions, the Arithmetic Logic Unit (ALU) which performs calculations, and registers that provide fast temporary storage.

  CPU 包含用于译码指令的控制单元（CU）、进行算术逻辑运算的 ALU，以及提供快速暂存的寄存器。

• Von Neumann architecture stores both program instructions and data in the same main memory, enabled by memory address and data buses.

  冯·诺依曼体系结构将程序指令和数据存储在同一主存储器中，通过地址总线和数据总线实现。

• The fetch‑decode‑execute cycle: the CPU fetches an instruction from memory, decodes it, and then executes it, repeating billions of times per second.

  取指–译码–执行周期：CPU 从内存取出一条指令，译码，然后执行，每秒重复数十亿次。

• Key registers: PC (Program Counter) holds the address of the next instruction; MAR (Memory Address Register) and MDR (Memory Data Register) handle memory reads/writes; ACC (Accumulator) stores ALU results.

  关键寄存器：PC（程序计数器）存放下一条指令地址；MAR（内存地址寄存器）和 MDR（内存数据寄存器）负责内存读写；ACC（累加器）暂存 ALU 结果。

• CPU performance is influenced by clock speed (GHz), number of cores, and cache size. Higher clock speed means more cycles per second; more cores allow parallel processing; larger cache reduces the need to access slower RAM.

  CPU 性能受时钟频率（GHz）、内核数和缓存大小影响。频率越高每秒周期越多；多核可并行处理；更大缓存减少对慢速 RAM 的访问。

3. Memory and Storage | 存储与存储器

• RAM (Random Access Memory) is volatile – it loses data when power is off. It stores the currently running programs and data actively used by the CPU.

  RAM（随机存取存储器）是易失性的——断电后数据会丢失。它存放当前运行的程序和 CPU 正在处理的数据。

• ROM (Read Only Memory) is non‑volatile and contains the bootstrap loader (BIOS) that starts the computer.

  ROM（只读存储器）是非易失性的，保存着启动计算机的引导程序（BIOS）。

• Virtual memory uses a portion of the hard disk as extra RAM when physical RAM is full. This slows down performance because disk access is much slower than RAM.

  虚拟内存将硬盘的一部分当作额外的 RAM 来使用，当物理 RAM 满时启用。这会降低性能，因为磁盘访问速度远慢于 RAM。

• Secondary storage devices: magnetic hard disk drives (HDDs) offer large capacity at low cost; solid state drives (SSDs) are faster and more durable but costlier per GB; optical discs (CD, DVD, Blu‑ray) are portable but have limited capacity.

  辅助存储设备：机械硬盘（HDD）容量大、成本低；固态硬盘（SSD）速度快、耐用，但每 GB 成本更高；光盘（CD、DVD、蓝光）便携但容量有限。

4. Networks and Topologies | 网络与拓扑

• LAN (Local Area Network) covers a small geographical area, uses private cabling or Wi‑Fi, and is usually owned by a single organisation. WAN (Wide Area Network) spans a large geographical area and often uses leased telecommunications lines.

  LAN（局域网）覆盖小的地理范围，使用私有线缆或 Wi‑Fi，通常由一个组织拥有。WAN（广域网）跨越大范围，通常租用电信线路。

• Client‑server model: a server provides resources or services, and clients request them. Peer‑to‑peer networks allow each computer to act as both client and server without a central authority.

  客户端–服务器模型：服务器提供资源或服务，客户端发出请求。点对点网络中每台计算机既可以作为客户端也可以作为服务器，没有中心管理者。

• Star topology connects every node to a central switch; if one cable fails only that node is affected. Bus topology uses a single backbone cable; a break in the backbone disables the entire segment.

  星型拓扑将所有节点连接到中央交换机；一根线缆故障只影响该节点。总线拓扑使用一条主干线缆；主干断裂会使整个网段瘫痪。

• IP address identifies a device on a network and can be static or dynamic. MAC address is a unique hardware identifier assigned to the network interface card and does not change.

  IP 地址标识网络中的设备，可以是静态或动态的。MAC 地址是网卡的唯一硬件标识，不会改变。

5. Network Protocols and the TCP/IP Stack | 网络协议与 TCP/IP 协议栈

• The TCP/IP four‑layer model: Application, Transport, Internet (IP), and Link (Network Interface). Each layer handles specific tasks, enabling reliable communication between diverse systems.

  TCP/IP 四层模型：应用层、传输层、网际层（IP）和网络接口层（链路层）。每层处理特定的任务，使异种系统之间能可靠通信。

• Application layer protocols: HTTP/HTTPS for web pages, FTP for file transfer, SMTP/POP/IMAP for email. HTTPS encrypts data using SSL/TLS.

  应用层协议：HTTP/HTTPS 用于网页传输，FTP 用于文件传输，SMTP/POP/IMAP 用于电子邮件。HTTPS 通过 SSL/TLS 加密数据。

• Transport layer: TCP provides error‑free, ordered delivery of data with acknowledgements (used for web, email). UDP is faster but connectionless, suitable for streaming and gaming.

  传输层：TCP 提供无差错、有序的确认交付（用于网页、邮件）。UDP 更快但无连接，适合流媒体和游戏。

• Internet layer delivers packets using IP addresses. Routers operate at this layer to forward data across networks.

  网际层使用 IP 地址传递数据包。路由器工作在这一层，将数据转发到不同网络。

• Link layer defines the physical transmission method and addressing (e.g., Ethernet, Wi‑Fi) and includes the MAC address.

  链路层定义物理传输方式和寻址（如以太网、Wi‑Fi），包含 MAC 地址。

6. Cyber Security | 网络安全

• Malware: viruses attach to files and spread when the file is run; worms self‑replicate without user action; trojans disguise themselves as legitimate software.

  恶意软件：病毒附着在文件上，当文件运行时传播；蠕虫无需用户干预即可自我复制；特洛伊木马伪装成合法软件。

• Social engineering attacks: phishing uses deceptive emails or websites to trick users into revealing sensitive information; blagging pretends to be someone authoritative to gain access.

  社会工程攻击：网络钓鱼利用欺骗性邮件或网站诱使用户泄露敏感信息；冒充权威人员以获取访问权限称为“blagging”。

• Brute‑force attacks try every possible password combination. Denial‑of‑service (DoS) floods a server with traffic, making it unavailable to legitimate users.

  暴力攻击尝试每一种可能的密码组合。拒绝服务攻击（DoS）用大量流量淹没服务器，使其对合法用户不可用。

• SQL injection inserts malicious SQL code into a web form input field, potentially exposing or destroying the database.

  SQL 注入将恶意 SQL 代码插入网页表单输入字段，可能泄露或破坏数据库。

• Protection measures: firewalls filter incoming and outgoing traffic; encryption scrambles data so only authorised parties can read it; user access levels limit what different users can do.

  防护措施：防火墙过滤进出流量；加密打乱数据，使只有授权方才能读取；用户访问级别限制不同用户的操作权限。

• Penetration testing and anti‑malware software help identify vulnerabilities before attackers exploit them. Regular software updates patch known security holes.

  渗透测试和反恶意软件有助于在攻击者利用之前发现漏洞。定期软件更新可修补已知的安全漏洞。

7. Logic Gates and Truth Tables | 逻辑门与真值表

Digital circuits are built from simple logic gates that process binary inputs.

数字电路由处理二进制输入的简单逻辑门构成。

A truth table lists all possible input combinations and the resulting output. Questions may ask you to draw or interpret a combination of gates.

真值表列出所有可能的输入组合及相应的输出结果。考题可能要求绘制或解释组合逻辑门。

8. Operating Systems and Utility Software | 操作系统与实用软件

• The operating system manages hardware and software resources. It provides a user interface, handles memory and processor scheduling, manages files and security, and controls peripheral devices.

  操作系统管理硬件和软件资源。它提供用户界面，处理内存和处理器调度，管理文件与安全，并控制外设设备。

• Multi‑tasking allows several programs to appear to run at the same time by rapidly switching the CPU between them.

  多任务处理通过在程序之间快速切换 CPU，使多个程序看似同时运行。

• Utility software performs maintenance tasks: disk defragmentation reorganises fragmented files to improve access speed; backup utilities create copies of data; compression utilities reduce file size.

  实用软件执行维护任务：磁盘碎片整理重新排列零散文件以提升访问速度；备份工具创建数据副本；压缩工具减少文件体积。

• Encryption utilities protect files by converting them into ciphertext. Antivirus software detects and removes malware. Firewall software monitors network traffic.

  加密工具通过将文件转换为密文来保护文件。反病毒软件检测并清除恶意软件。防火墙软件监控网络流量。

9. Programming Fundamentals | 编程基础

• Data types: integer (whole numbers), real/float (decimal numbers), Boolean (true/false), character (single symbol), and string (sequence of characters). Know how to cast between them.

  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（字符序列）。要掌握它们之间的强制类型转换。

• Constants are named values that do not change during execution, improving code clarity. Variables store values that can be modified.

  常量是在程序执行期间不变的命名值，可提高代码可读性。变量存放可以修改的值。

• Selection: if, else-if, else statements allow decision making. Indentation is crucial in Python to define the block.

  选择结构：if、else-if、else 语句用于决策。Python 中缩进对于定义代码块至关重要。

• Iteration: for loops repeat a block a fixed number of times; while loops repeat as long as a condition is true. Beware of infinite loops.

  迭代：for 循环将代码块重复执行固定次数；while 循环在条件为真时一直重复。注意避免无限循环。

• Arrays (lists) store multiple items under one name. 1D arrays are like a row of values; 2D arrays form a grid accessed by row and column indices.

  数组（列表）用一个名字存放多个元素。一维数组像一行值；二维数组构成由行和列索引访问的网格。

• Subroutines: procedures perform a task without returning a value; functions return a value. Parameters pass data into a subroutine.

  子程序：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。

10. Algorithms and Computational Thinking | 算法与计算思维

• Decomposition breaks a complex problem into smaller, more manageable parts. Abstraction removes unnecessary details to focus on the key features.

  分解将复杂问题拆分成更小、更易管理的部分。抽象化去除不必要的细节，专注于关键特征。

• Algorithms can be expressed using flowcharts (shapes for processes, decisions, start/stop) or pseudocode (structured, human‑readable notation).

  算法可以用流程图（不同形状表示处理、判断、开始/结束）或伪代码（结构化的、易读的符号）来描述。

• Linear search checks each element in order until the target is found or the list ends; works on unsorted data. O(n) time.

  线性搜索按顺序检查每个元素，直到找到目标或到达列表末尾；适用于未排序数据。时间复杂度 O(n)。

• Binary search repeatedly divides a sorted list in half; it is much faster, O(log n), but requires the data to be sorted first.

  二分搜索不断将有序列表对半分；速度更快，时间复杂度 O(log n)，但要求数据必须已经排序。

• Bubble sort repeatedly swaps adjacent elements if they are in the wrong order; it is simple but inefficient for large datasets.

  冒泡排序反复交换顺序错误的相邻元素；它简单但对大数据集效率低。

• Merge sort divides the list into halves, recursively sorts them, and then merges the sorted halves; it is consistently O(n log n) and more efficient for large data.

  归并排序将列表对半分，递归排序，再合并已排序的子列表；时间复杂度稳定在 O(n log n)，对大数据更高效。

11. Ethical, Legal and Environmental Concerns | 伦理、法律与环境问题

• The Data Protection Act sets rules for storing and processing personal data, requiring fair, secure, and lawful handling. Computer Misuse Act makes unauthorised access to systems illegal.

  数据保护法规定了存储和处理个人数据的规则，要求公平、安全、合法地处理。计算机滥用法将未经授权访问系统定为非法。

• Copyright and intellectual property protect software, music, and images from unauthorised copying. Plagiarism is using someone else’s work without credit.

  版权和知识产权保护软件、音乐、图像不被非法复制。剽窃是指不注明出处就使用他人的作品。

• AI ethics: issues around bias in data, job displacement, and accountability for autonomous decisions must be considered.

  人工智能伦理：必须考虑数据偏见、工作岗位替代以及自主决策的责任归属等问题。

• Environmental impact: manufacturing devices consumes raw materials and energy; e‑waste contains hazardous substances. Data centres demand large amounts of electricity for power and cooling.

  环境影响：制造设备消耗原材料和能源；电子废弃物含有有害物质。数据中心需要大量电力运行和冷却。

• The digital divide – the gap between those with and without access to technology – raises concerns about inequality in education

  Published by TutorHao | IGCSE Computer Science Revision Series | aleveler.com

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