📚 IGCSE AQA Computer Science: Mind Map Quick Revision | IGCSE AQA 计算机：思维导图速记
Mind maps are powerful visual tools for organising and memorising key concepts in IGCSE Computer Science. By linking ideas in a radial structure, you can quickly recall topics ranging from algorithms to networks. This article provides a structured quick revision using the mind map approach, covering all major topics in the AQA specification.
思维导图是一种强大的视觉工具，用于组织和记忆 IGCSE 计算机科学中的关键概念。通过以放射状结构连接各个想法，你可以快速回忆起从算法到网络的各种主题。本文提供了一种使用思维导图法的结构化快速复习，涵盖了 AQA 考试大纲中的所有主要主题。
1. Algorithmic Thinking | 算法思维
Computational thinking involves three key techniques: abstraction, decomposition, and algorithmic thinking.
计算思维涉及三种关键技术：抽象、分解和算法思维。
Abstraction is the process of filtering out unnecessary details to focus on what is important.
抽象是过滤掉不必要的细节，专注于重要内容的过程。
Decomposition means breaking a complex problem into smaller, more manageable parts.
分解意味着将复杂问题拆分成更小、更易管理的部分。
Algorithmic thinking is the ability to design step-by-step solutions that can be implemented as programs.
算法思维是设计能够被实现为程序的逐步解决方案的能力。
A good algorithm must be clear, precise, and terminate after a finite number of steps.
一个好的算法必须清晰、精确，并在有限步骤后终止。
2. Programming Fundamentals | 编程基础
Variables store data values and have a data type such as integer, real, Boolean, character, or string.
变量存储数据值，并具有数据类型，如整数、实数、布尔型、字符或字符串。
The three basic programming constructs are sequence, selection (if-else), and iteration (for, while loops).
三种基本编程结构是顺序、选择（if-else）和迭代（for、while 循环）。
A string manipulation function like len() returns the length, and sub-string operations extract parts of a string.
字符串操作函数如 len() 返回长度，子串操作用于提取字符串的一部分。
Arrays (or lists) hold multiple values of the same type under a single identifier and can be one-dimensional or two-dimensional.
数组（或列表）在一个标识符下存储多个相同类型的值，可以是一维或二维的。
Records (structures) group related data items of different types into one unit, with each item called a field.
记录（结构）将不同类型的数据项组合成一个单元，每个数据项称为字段。
3. Data Representation: Numbers & Text | 数据表示：数字与文本
All data in a computer is stored as binary digits (bits), either 0 or 1.
计算机中的所有数据都存储为二进制数字（比特），即 0 或 1。
Denary (base-10) numbers can be converted to binary. For example, 13 in denary is 1101₂.
十进制（基数为10）数可以转换为二进制。例如，十进制13是1101₂。
Hexadecimal (base-16) uses digits 0-9 and letters A-F. One hex digit represents 4 bits, making it compact for representing binary.
十六进制（基数为16）使用数字0-9和字母A-F。一个十六进制数字表示4个比特，使其用于表示二进制更加紧凑。
Character sets such as ASCII (7-bit) and Unicode map characters to binary codes. ASCII covers English, while Unicode covers all languages and emojis.
字符集如 ASCII（7位）和 Unicode 将字符映射为二进制代码。ASCII 覆盖英语，而 Unicode 覆盖所有语言和表情符号。
Adding in binary follows simple rules: 0+0=0, 0+1=1, 1+0=1, 1+1=0 carry 1.
二进制加法遵循简单规则：0+0=0、0+1=1、1+0=1、1+1=0并进位1。
4. Data Representation: Images & Sound | 数据表示：图像与声音
Bitmap images are made of a grid of pixels, each with a binary code for its colour. Higher colour depth (bits per pixel) gives more colours but larger file size.
位图图像由像素网格组成，每个像素用一个二进制代码表示其颜色。更高的色深（每像素位数）提供更多颜色，但文件大小更大。
Image resolution is the number of pixels per inch (ppi) or the total pixel dimensions. Higher resolution means sharper images but larger storage.
图像分辨率是每英寸像素数 (ppi) 或总像素尺寸。分辨率越高，图像越清晰，但存储需求更大。
Sound is sampled by taking measurements of the sound wave amplitude at regular intervals. Sampling rate (Hz) and bit depth affect quality and file size.
声音通过定期测量声波振幅来采样。采样率（赫兹）和位深影响音质和文件大小。
Sound file size (bits) = sampling rate × bit depth × duration (seconds) × number of channels.
声音文件大小（比特）= 采样率 × 位深 × 时长（秒）× 声道数。
Compression can be lossless (all original data can be recovered) or lossy (some data is permanently removed to reduce size).
压缩可以是有损（丢失部分数据，无法完全恢复）或无损（可以完全恢复原始数据）。
5. Computer Systems: CPU & Memory | 计算机系统：中央处理器与内存
The Central Processing Unit (CPU) follows the fetch-decode-execute cycle to process instructions.
中央处理器 (CPU) 遵循取指-解码-执行周期来处理指令。
The main components of a CPU are the Control Unit (CU), Arithmetic Logic Unit (ALU), registers (e.g., PC, MAR, MDR) and cache memory.
CPU 的主要组件包括控制单元 (CU)、算术逻辑单元 (ALU)、寄存器（如 PC、MAR、MDR）和高速缓存。
The clock speed (in GHz) determines how many fetch-decode-execute cycles are performed per second.
时钟速度（以 GHz 为单位）决定了每秒执行多少次取指-解码-执行周期。
RAM (Random Access Memory) is volatile main memory that holds running programs and data currently in use. ROM is non-volatile and stores boot-up instructions.
RAM（随机存取存储器）是易失性主存，保存正在运行的程序和使用的数据。ROM 是非易失性的，存储启动指令。
The von Neumann architecture stores both program instructions and data in the same memory and uses buses (address, data, control) to transfer information.
冯·诺依曼体系结构将程序指令和数据存储在同一内存中，并使用总线（地址、数据、控制总线）传输信息。
6. Storage Devices | 存储设备
Primary storage (RAM, ROM) is directly accessed by the CPU, and is fast but has limited capacity and is volatile (except ROM).
主存储器（RAM、ROM）由 CPU 直接访问，速度快但容量有限，且易失（除 ROM 外）。
Secondary storage (HDD, SSD, optical, cloud) stores data permanently. HDD uses magnetic platters, SSD uses flash memory with no moving parts.
辅助存储器（硬盘、固态硬盘、光盘、云存储）永久存储数据。HDD 使用磁性盘片，SSD 使用闪存，无移动部件。
Optical discs (CD, DVD, Blu-ray) use lasers to read/write data. Capacity increases from CD (~700MB) to Blu-ray (~25GB per layer).
光盘（CD、DVD、蓝光）使用激光读写数据。容量从 CD（约 700MB）增加到蓝光（每层约 25GB）。
Virtual memory uses a portion of the hard drive as an extension of RAM when RAM is full, but it is much slower.
虚拟内存使用硬盘的一部分作为 RAM 的扩展，当 RAM 已满时使用，但速度慢得多。
Cloud storage allows data to be stored remotely on servers accessed via the internet, offering scalability and accessibility.
云存储允许将数据远程存储在通过互联网访问的服务器上，提供可扩展性和可访问性。
7. Computer Networks | 计算机网络
A network is two or more computers connected to share resources. LAN covers a small area; WAN covers a wide area like the internet.
网络是两台或更多连接起来共享资源的计算机。LAN 覆盖小区域；WAN 覆盖大区域，如互联网。
Common topologies include star (all connect to a central switch/hub) and mesh (each node connects to many others). Star is popular due to ease of troubleshooting.
常见拓扑包括星型（所有连接到中央交换机/集线器）和网状（每个节点连接到许多其他节点）。星型因便于故障排除而流行。
Protocols are sets of rules for communication: TCP/IP (transmission), HTTP/HTTPS (web), FTP (file transfer), SMTP/POP/IMAP (email).
协议是通信规则集：TCP/IP（传输）、HTTP/HTTPS（网页）、FTP（文件传输）、SMTP/POP/IMAP（电子邮件）。
The TCP/IP 4-layer model consists of Application, Transport, Internet, and Network Interface layers.
TCP/IP 四层模型由应用层、传输层、互联网层和网络接口层组成。
Packet switching breaks data into packets that travel independently through the network and are reassembled at the destination.
分组交换将数据分成数据包，这些数据包独立通过网络传输，并在目的地重新组装。
8. Cyber Security | 网络安全
Malware includes viruses (attach to files), worms (self-replicate across networks), trojans (disguised as legitimate), spyware, and ransomware.
恶意软件包括病毒（附加到文件）、蠕虫（在网络中自我复制）、特洛伊木马（伪装为合法程序）、间谍软件和勒索软件。
A phishing attack uses fake emails or websites to trick users into giving away personal information like passwords.
网络钓鱼攻击使用伪造的电子邮件或网站欺骗用户泄露密码等个人信息。
Brute-force attacks try all possible password combinations; strong passwords (mix of characters, long) and account lockout policies help prevent them.
暴力破解攻击尝试所有可能的密码组合；强密码（字符组合、足够长）和账户锁定策略有助于防止它们。
Encryption scrambles data using an algorithm and a key; only those with the correct key can decrypt it. Symmetric and asymmetric encryption are two types.
加密使用算法和密钥对数据进行扰乱；只有拥有正确密钥的人才能解密。对称加密和非对称加密是两种类型。
Penetration testing involves simulating attacks to identify security weaknesses before malicious hackers can exploit them.
渗透测试包括模拟攻击，以在恶意黑客利用之前识别安全弱点。
9. Databases & SQL | 数据库与 SQL
A relational database stores data in tables linked by primary keys and foreign keys to reduce redundancy.
关系数据库将数据存储在通过主键和外键链接的表中，以减少冗余。
A primary key uniquely identifies each record in a table. A foreign key in one table links to the primary key of another.
主键唯一标识表中的每条记录。一个表中的外键链接到另一个表的主键。
SQL (Structured Query Language) is used to query databases. SELECT, FROM, WHERE are common clauses.
SQL（结构化查询语言）用于查询数据库。SELECT、FROM、WHERE 是常用子句。
Example: SELECT name, age FROM Students WHERE age > 15 ORDER BY name ASC;
示例：SELECT name, age FROM Students WHERE age > 15 ORDER BY name ASC;
INSERT, UPDATE, DELETE are used to modify data. Data validation (e.g., format check, range check) ensures data integrity.
INSERT、UPDATE、DELETE 用于修改数据。数据验证（如格式检查、范围检查）确保数据完整性。
10. Impacts of Computing | 计算机的影响
The digital divide is the gap between those who have access to modern digital technology and those who do not.
数字鸿沟是指能够访问现代数字技术的人与无法访问的人之间的差距。
Legal issues include the Data Protection Act (controls how personal data is used) and Computer Misuse Act (makes hacking and virus creation illegal).
法律问题包括《数据保护法》（规范个人数据的使用）和《计算机滥用法》（将黑客攻击和病毒制造定为非法）。
The Copyright, Designs and Patents Act protects intellectual property and prevents software piracy.
《版权、设计和专利法》保护知识产权，防止软件盗版。
Environmental impacts: manufacturing devices uses resources and energy; e-waste is a growing problem. Recycling and energy-efficient design help reduce impact.
环境影响：制造设备消耗资源和能源；电子废物是一个日益严重的问题。回收和节能设计有助于减少影响。
Open source software can be modified and shared; proprietary software is closed and usually requires a license fee.
开源软件可以修改和共享；专有软件是封闭的，通常需要许可费。
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