📚 AQA GCSE Computer Science: Complete Knowledge Organiser & Revision Guide | AQA GCSE 计算机：知识点梳理与复习指南
This comprehensive revision guide covers the entire AQA GCSE Computer Science specification (8525), organised into clear, exam-focused sections. Each topic below is paired with the key concepts, terminology, and practical examples you need to secure top marks in Paper 1 (Computational Thinking and Programming Skills) and Paper 2 (Computing Concepts).
本复习指南完整覆盖 AQA GCSE 计算机科学考纲（8525），按清晰且紧扣考试的章节进行梳理。以下每个主题均配有关键概念、术语和实用示例，帮助你在试卷一（计算思维与编程技能）和试卷二（计算概念）中争取高分。
1. Fundamentals of Algorithms | 算法基础
An algorithm is a precise, step-by-step set of instructions for solving a problem. You must be able to represent algorithms using pseudocode, flowcharts, and written descriptions, and to trace them systematically.
算法是为解决问题而设计的精确、逐步的指令集合。你必须能够用伪代码、流程图和文字描述来表示算法，并能够系统地进行手工追踪（trace）。
Computational thinking: breaking down problems (decomposition), spotting patterns (pattern recognition), focusing on important details (abstraction), and designing step-by-step solutions (algorithmic thinking).
计算思维：分解问题（分解）、发现规律（模式识别）、聚焦重要细节（抽象）以及设计逐步解决方案（算法思维）。
Flowchart symbols: rounded rectangles for start/stop, rectangles for processes, diamonds for decisions, parallelograms for input/output, and arrows for flow of control.
流程图符号：圆角矩形表示开始/结束，矩形表示处理，菱形表示判断，平行四边形表示输入/输出，箭头表示控制流向。
Pseudocode uses everyday English mixed with programming structures such as IF, THEN, ELSE, WHILE, FOR, and REPEAT. AQA provides a dedicated pseudocode guide — learn it thoroughly.
伪代码使用日常英语混合编程结构，如 IF、THEN、ELSE、WHILE、FOR 和 REPEAT。AQA 提供了专门的伪代码指南——务必彻底掌握。
ar search on [4, 9, 1, 7] for 7 → check 4 (no), 9 (no), 1 (no), 7 (yes) → found at index 3
示例：在 [4, 9, 1, 7] 中线性查找 7 → 检查 4（否）、9（否）、1（否）、7（是）→ 在下标 3 处找到。
2. Sorting and Searching Algorithms | 排序与查找算法
You must know how to perform and compare three sorting algorithms and two searching algorithms, including their time efficiency in terms of 'best' and 'worst' cases.
你必须掌握三种排序算法和两种查找算法的执行过程与比较，包括它们在“最佳”和“最差”情况下的时间效率。
Bubble sort: repeatedly compare adjacent items and swap them if they are in the wrong order. After each pass, the largest remaining item 'bubbles' to the end.
冒泡排序：反复比较相邻项，如果顺序错误则交换。每一轮结束后，剩余项中的最大值“冒泡”到末尾。
Merge sort: divide the list into single items, then repeatedly merge pairs in sorted order. It is much more efficient than bubble sort for large lists.
归并排序：将列表不断二分直到单项，然后按排序顺序反复合并成对。对于大规模列表，它比冒泡排序高效得多。
Insertion sort: take each item in turn and insert it into its correct position among the already-sorted items to its left.
插入排序：依次取出每一项，并将其插入到左侧已排序部分中的正确位置。
Linear search: check each item in order until the target is found or the list ends. Works on unsorted data.
线性查找：按顺序检查每一项，直到找到目标或列表结束。适用于未排序数据。
Binary search: only works on sorted lists. Compare the middle item; if it is too high, search the left half; if too low, search the right half. Repeat until found.
二分查找：仅适用于已排序列表。比较中间项；如果目标值较大，则在右半部分查找；如果较小，则在左半部分查找。重复直到找到。
| Algorithm | Best case | Worst case |
| Bubble sort | O(n) | O(n²) |
| Merge sort | O(n log n) | O(n log n) |
| Insertion sort | O(n) | O(n²) |
| Linear search | O(1) | O(n) |
| Binary search | O(1) | O(log n) |
3. Fundamentals of Data Representation | 数据表示基础
Computers use binary because they have two stable states (on/off). You must convert between denary and binary and understand why hexadecimal is used as a compact notation.
计算机使用二进制是因为它们有两种稳定状态（开/关）。你必须掌握十进制与二进制之间的转换，并理解为什么十六进制被用作紧凑记数法。
its. A kilobyte (KB) is 1000 bytes; a kibibyte (KiB) is 1024 bytes. Know both conventions.
位（bit）= 二进制数字（0 或 1）。半字节（nibble）= 4 位。字节（byte）= 8 位。1 千字节（KB）= 1000 字节；1 千位字节（KiB）= 1024 字节。两种规范都要掌握。
Denary to binary: repeatedly divide by 2 and record remainders. Binary to denary: add up place values (128, 64, 32, 16, 8, 4, 2, 1).
十进制转二进制：反复除以 2 并记录余数。二进制转十进制：将各数位值（128、64、32、16、8、4、2、1）相加。
Hexadecimal uses digits 0-9 and letters A-F. Each hex digit represents exactly 4 bits, making it easy to shorten long binary strings.
十六进制使用数字 0-9 和字母 A-F。每个十六进制位恰好对应 4 个二进制位，因此可以轻松缩短长二进制串。
Binary 10110110 = 128+32+16+4+2 = 182 denary = B6 hex
二进制 10110110 = 128+32+16+4+2 = 十进制 182 = 十六进制 B6
Characters are stored using ASCII (7 bits, 128 characters) or Unicode (larger sets for all world languages). Images use pixels, each stored as a binary colour code; resolution and colour depth determine file size.
字符通过 ASCII（7 位，128 个字符）或 Unicode（覆盖全球各种语言的大字符集）存储。图像使用像素，每个像素存储为二进制颜色代码；分辨率和颜色深度决定文件大小。
Sound is sampled at regular intervals; sample rate, bit depth, and the number of channels control quality. Compression reduces file size: lossless preserves all data, lossy discards some data for smaller files.
声音按固定时间间隔采样；采样率、位深度和声道数决定音质。压缩减少文件大小：无损压缩保留全部数据，有损压缩丢弃部分数据以换取更小文件。
4. Computer Systems | 计算机系统
The CPU (Central Processing Unit) is the brain of the computer. It fetches, decodes, and executes instructions stored in memory. The von Neumann architecture uses a single memory for both data and instructions.
CPU（中央处理器）是计算机的大脑。它取指、译码并执行存储在内存中的指令。冯·诺依曼体系结构使用统一的内存来存储数据和指令。
Registers: PC (Program Counter) holds the address of the next instruction; MAR (Memory Address Register) holds the address being read/written; MDR (Memory Data Register) holds data transferred; ACC (Accumulator) stores arithmetic/logic results.
寄存器：PC（程序计数器）存放下一条指令的地址；MAR（内存地址寄存器）存放正在读写的地址；MDR（内存数据寄存器）存放传输的数据；ACC（累加器）存储算术/逻辑运算结果。
Fetch: copy address from PC to MAR; READ memory; transfer instruction to MDR; copy MDR to CIR; increment PC. Decode: interpret the instruction. Execute: carry it out.
取指：将 PC 中的地址复制到 MAR；读取内存；将指令传输到 MDR；将 MDR 复制到 CIR；PC 加一。译码：解释指令。执行：完成操作。
Clock speed (GHz), cache size, and the number of cores affect CPU performance. Embedded systems are computers built into other devices with a dedicated function (e.g., a washing machine controller).
时钟频率（GHz）、缓存大小和核心数影响 CPU 性能。嵌入式系统是内置于其他设备、拥有专用功能的计算机（例如洗衣机控制器）。
5. Memory and Storage | 内存与存储
Primary storage is directly accessed by the CPU. RAM is volatile and holds the currently running programs and data; ROM is non-volatile and stores bootstrap code (firmware) that runs when the computer starts.
主存储器由 CPU 直接访问。RAM 是易失性内存，存放当前运行的程序和数据；ROM 是非易失性存储器，存放计算机启动时运行的引导程序（固件）。
Virtual memory uses part of the secondary storage to extend RAM when it is full. It is much slower than RAM because disk access is slower.
当 RAM 已满时，虚拟内存使用辅存的一部分来扩展内存。由于磁盘访问更慢，其速度远低于 RAM。
Secondary storage types: magnetic (HDD, cheap, high capacity), optical (CD/DVD, portable), solid state (SSD, fast, durable, no moving parts).
辅助存储类型：磁性存储（HDD，便宜、容量大）、光学存储（CD/DVD，便携）、固态存储（SSD，快速、耐用、无机械部件）。
| Storage | Speed | Capacity | Cost per GB |
| HDD | Medium | Large | Low |
| SSD | Very fast | Medium | Higher |
| Optical | Slow | Low | Very low |
6. Wired and Wireless Networks | 有线和无线网络
A network connects multiple devices so they can share data, software, and peripherals. LAN (Local Area Network) covers a small area; WAN (Wide Area Network) spans a large geographical area.
网络将多个设备连接起来，使它们能够共享数据、软件和外围设备。LAN（局域网）覆盖较小区域；WAN（广域网）跨越较大地理范围。
Ethernet cables use copper wires (UTP/STP) to transmit data electrically. Fibre-optic cables use light pulses for very fast, long-distance links resistant to interference.
以太网线使用铜线（UTP/STP）以电信号传输数据。光纤使用光脉冲进行高速、远距离传输且抗干扰能力强。
Wi-Fi uses radio waves (typically 2.4 GHz or 5 GHz). It is convenient but can suffer from interference, signal weakening, and security risks.
Wi-Fi 使用无线电波（通常为 2.4 GHz 或 5 GHz）。它使用方便，但可能受到干扰、信号衰减和安全风险的影响。
Network topologies: star (all devices connect to a central switch) and mesh (devices connect to multiple others, providing redundancy).
网络拓扑：星型（所有设备连接到中央交换机）和网状（设备之间多点连接，提供冗余）。
Protocols: TCP/IP (splits data into packets and routes them), HTTP/HTTPS (web pages), FTP (file transfer), SMTP (email sending), POP3 (email receiving), and Ethernet (wired framing).
协议：TCP/IP（将数据分包并路由）、HTTP/HTTPS（网页）、FTP（文件传输）、SMTP（发送邮件）、POP3（接收邮件）以及以太网（有线帧格式）。
7. Network Security and Cyber Threats | 网络安全与网络威胁
Network security protects data and systems from unauthorised access and damage. You must be able to describe common threats and the countermeasures used to prevent them.
网络安全保护数据和系统免受未经授权的访问和损害。你必须能够描述常见威胁及用于防范这些威胁的应对措施。
Malware: malicious software including viruses, worms, trojans, spyware, and ransomware. It can delete files, steal data, or encrypt files until a ransom is paid.
恶意软件：包括病毒、蠕虫、木马、间谍软件和勒索软件在内的恶意程序。它可能删除文件、窃取数据或加密文件以索要赎金。
Phishing: deceptive emails or messages pretending to be legitimate to trick users into revealing passwords or bank details.
钓鱼攻击：伪装成合法机构的欺骗性邮件或消息，诱骗用户泄露密码或银行信息。
Brute-force attack: automatically trying every possible password until one works. Countermeasures include strong passwords and account lockout.
暴力破解攻击：自动尝试所有可能的密码，直到猜中为止。对策包括强密码和账户锁定。
Defences: firewalls (filter incoming/outgoing traffic), anti-malware software, encryption, strong authentication (e.g., 2FA), and user access levels.
防御措施：防火墙（过滤进出的流量）、反恶意软件、加密、强身份验证（如双因素认证）和用户访问权限分级。
8. Ethical, Legal, and Environmental Impacts | 道德、法律与环境影响
Computing technology creates ethical and legal dilemmas. You need to evaluate the impacts of technology on people, society, and the environment, not just memorise definitions.
计算技术引发了道德与法律难题。你需要评估技术对人、社会和环境的影响，而不仅仅是记忆定义。
Legislation: the Computer Misuse Act 1990 (unauthorised access), the Data Protection Act 2018 (GDPR — lawful handling of personal data), the Copyright, Designs and Patents Act 1988 (protects software and creative works), and the Freedom of Information Act 2000.
法律：1990 年《计算机滥用法》（未经授权访问）、2018 年《数据保护法》（GDPR——合法处理个人数据）、1988 年《版权、外观设计和专利法》（保护软件和创意作品）以及 2000 年《信息自由法》。
Ethical issues: privacy vs surveillance, access to personal data, algorithms making biased decisions, and the impact of automation on jobs.
道德问题：隐私与监控之间的权衡、个人数据的获取范围、算法做出有偏见的决策，以及自动化对就业的影响。
Environmental impact: energy consumption of data centres, electronic waste (e-waste), and the carbon footprint of manufacturing devices. Consider reduce, reuse, recycle strategies.
环境影响：数据中心的能源消耗、电子垃圾（e-waste）以及制造设备的碳足迹。需考虑减少、复用、回收等策略。
9. Programming Fundamentals | 编程基础
AQA expects you to write, read, and trace programs in Python-style syntax. The exam frequently includes 6-mark programming questions where you must design and write correct code.
AQA 要求你使用 Python 风格语法编写、阅读和追踪程序。考试中常有 6 分编程题，要求你设计和编写正确的代码。
Variables: named memory locations that store values. Constants: values that do not change. Use meaningful names like
scorerather thans.变量：用于存储值的命名内存单元。常量：值固定不变。使用有意义的名称如
score，而不是s。Sequence: instructions executed in order. Selection: IF, ELIF, ELSE chooses a path. Iteration: FOR (count-controlled) and WHILE (condition-controlled) loops repeat code.
顺序结构：指令按顺序执行。选择结构：IF、ELIF、ELSE 选择执行路径。循环结构：FOR（计数控制）和 WHILE（条件控制）重复执行代码块。
Arrays (lists) store multiple items in one variable:
scores = [12, 45, 67]. The first index is 0.数组（列表）将多个项存储在一个变量中：
scores = [12, 45, 67]。第一个下标是 0。Functions/subroutines reduce repetition, improve readability, and make testing easier. They use parameters to pass data and RETURN to give back results.
函数/子程序减少重复代码，提高可读性，并便于测试。它们使用参数传入数据，并通过 RETURN 返回结果。
if score >= 50: print('Pass') else: print('Fail')
如果 score >= 50：输出 'Pass' 否则：输出 'Fail'
10. Data Types, Operators, and String Handling | 数据类型、运算符与字符串处理
Programming requires selecting the correct data type and using operators to compare values and process strings. Data types include integer, real (float), boolean, character, and string.
编程需要选择正确的数据类型，并运用运算符来比较值和处理字符串。数据类型包括整型、实型（浮点）、布尔型、字符型和字符串型。
Integer: whole numbers (5). Real/float: numbers with decimals (3.14). Boolean: True or False. Character: single letter 'A'. String: sequence of characters 'Hello'.
整型：整数（5）。实型/浮点：带小数的数（3.14）。布尔型：True 或 False。字符：单个字母 'A'。字符串：字符序列 'Hello'。
Arithmetic operators: + - * / // (integer division) % (modulo) ** (power). Assignment:
=assigns a value;==tests equality.算术运算符：+ - * / //（整数除法）%（取模）**（幂）。赋值：
=用于赋值；==用于判断相等。String operations: length (LEN), substring, concatenation (+), upper/lower case, and converting between strings and integers using
int()andstr().字符串操作：长度（LEN）、子串、拼接（+）、大小写转换，以及用
int()和str()进行字符串与整数之间的转换。
11. Boolean Logic | 布尔逻辑
Logic gates are the hardware building blocks of circuits. AQA requires you to know AND, OR, NOT gates (and combined gates like NAND and NOR). Truth tables show the output for every possible input.
逻辑门是电路的基本硬件构件。AQA 要求你掌握 AND、OR、NOT 门（以及 NAND、NOR 等组合门）。真值表列出每种可能输入对应的输出。
AND: output is 1 only when both inputs are 1. OR: output is 1 when at least one input is 1. NOT: output is the opposite of the input.
AND：仅当两个输入均为 1 时输出为 1。OR：至少一个输入为 1 时输出为 1。NOT：输出与输入相反。
| A | B | A AND B | A OR B | NOT A |
| 0 | 0 | 0 | 0 | 1 |
| 0 | 1 | 0 | 1 | 1 |
| 1 | 0 | 0 | 1 | 0 |
| 1 | 1 | 1 | 1 | 0 |
In AQA questions, you may be asked to draw logic circuits or complete truth tables for a combination of gates.
在 AQA 考试中，你可能需要画出逻辑电路图，或为组合门电路完成真值表。
12. Translators and IDEs | 翻译器与集成开发环境
High-level languages (Python, Java) are easier for humans to read. They must be translated into machine code before the CPU can execute them. Low-level languages (assembly and machine code) are faster but harder to write.
高级语言（Python、Java）更易于人类阅读。它们必须先翻译成机器码，CPU 才能执行。低级语言（汇编语言和机器码）速度更快，但编写更困难。
Compiler: translates the entire program in one go. It produces an executable file and reports all errors at compile time. Interpreter: translates and executes line by line — good for debugging but slower.
编译器：一次性翻译整个程序，生成可执行文件并在编译时报告所有错误。解释器：逐行翻译并执行——便于调试但速度较慢。
Assembler: converts assembly language into machine code. Assembly uses mnemonics like LDA (load), ADD, and STO (store).
汇编器：将汇编语言转换为机器码。汇编使用助记符如 LDA（加载）、ADD（加）和 STO（存储）。
IDE features: editor (syntax highlighting, autocomplete), debugger (breakpoints, step-through, variable watch), runtime environment, and helpful error diagnostics.
IDE 功能：编辑器（语法高亮、自动补全）、调试器（断点、单步执行、变量监视）、运行时环境以及有用的错误诊断。
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