📚 Mind Map Quick Revision for IB & CCEA Computer Science | IB & CCEA 计算机科学思维导图速记
This article presents a mind-map-style quick revision guide for students preparing for IB Computer Science and CCEA A-Level Computer Science. Core topics are broken down into bite-sized concept nodes, each explained in English and Chinese to reinforce bilingual understanding and memorisation. Use these structured summaries as checklists or as a visual recall map before your exams.
本文为准备 IB 计算机科学和 CCEA A-level 计算机科学考试的学生提供思维导图式速记指南。核心主题被拆解为小块概念节点，每个节点均以英文和中文双语解释，强化理解和记忆。可将这些结构化摘要用作考前自检清单或形象化记忆地图。
1. System Fundamentals & Architecture | 系统基础与体系结构
A computer system consists of hardware, software, data, users and processes working together. The fundamental architecture follows the input-process-output model, where data enters through input devices, is processed by the CPU according to stored instructions, and results are delivered via output devices.
计算机系统由硬件、软件、数据、用户和协同工作的进程组成。其基本架构遵循输入-处理-输出模型：数据通过输入设备进入，由 CPU 按照存储的指令进行处理，结果通过输出设备交付。
The Von Neumann architecture stores both data and programs in the same memory; instructions are fetched, decoded and executed sequentially. In contrast, Harvard architecture uses separate memory and buses for data and instructions, allowing simultaneous access and faster operation in embedded systems.
冯·诺依曼体系结构将数据和程序存储在同一个内存中；指令按顺序被取出、解码并执行。相比之下，哈佛结构为数据和指令使用独立的内存和总线，允许同时访问，在嵌入式系统中运行更快。
Key components include the ALU (Arithmetic Logic Unit) for computation, the Control Unit (CU) for directing operations, registers for temporary storage, and cache memory to speed up data access. The system bus carries data, addresses and control signals.
关键组件包括：用于计算的算术逻辑单元(ALU)、用于指挥操作的控制器(CU)、用于临时存储的寄存器，以及加速数据访问的高速缓存(Cache)。系统总线则传输数据、地址和控制信号。
2. Data Representation & Number Systems | 数据表示与数制
Computers use binary (base-2) to represent all data. Numbers, characters, images and sound are encoded as sequences of bits. Converting between binary, denary (base-10) and hexadecimal (base-16) is essential for debugging and memory addressing.
计算机使用二进制表示所有数据。数字、字符、图像和声音都被编码为位序列。二进制、十进制和十六进制之间的转换对于调试和内存寻址至关重要。
Hexadecimal uses digits 0-9 and A-F; each hex digit represents four bits (a nibble). For example, 1011 1101₂ = BD₁₆. Binary addition follows simple rules: 0+0=0, 0+1=1, 1+1=0 carry 1.
十六进制使用数字 0-9 和字母 A-F；每个十六进制位代表四个比特（半字节）。例如 1011 1101₂ = BD₁₆。二进制加法遵循简单规则：0+0=0，0+1=1，1+1=0 进位 1。
Negative integers are stored using sign-and-magnitude or two’s complement. Two’s complement representation makes subtraction possible by addition: invert all bits and add 1 to get the negative of a number. Floating-point numbers (e.g., IEEE 754) store a number as sign × mantissa × 2exponent.
负整数使用原码或二进制补码存储。二进制补码表示法通过加法实现减法：将所有位取反并加 1 即可得到一个数的负数。浮点数（如 IEEE 754）以符号×尾数×2指数 的形式存储数字。
Character sets: ASCII (7-bit, 128 chars), extended ASCII (8-bit, 256), Unicode (up to 32-bit, covering all languages).
字符集：ASCII（7位，128个字符）、扩展 ASCII（8位，256个）、Unicode（最多32位，涵盖所有语言）。
3. Boolean Algebra & Logic Gates | 布尔代数与逻辑门
Boolean algebra operates on binary variables with values TRUE (1) or FALSE (0). Basic operations are AND (conjunction), OR (disjunction) and NOT (negation). Gates implement these operations in digital circuits.
布尔代数对取值为 TRUE(1) 或 FALSE(0) 的二进制变量进行运算。基本运算为与(AND)、或(OR)和非(NOT)。逻辑门在数字电路中实现这些运算。
AND gate: output is 1 only when all inputs are 1 (A ∧ B). OR gate: output is 1 when at least one input is 1 (A ∨ B). NOT gate inverts the input (¬A). NAND and NOR gates are universal gates because any logic function can be built using only NAND or only NOR gates.
与门：只有当所有输入都为 1 时输出才为 1 (A ∧ B)。或门：至少一个输入为 1 时输出为 1 (A ∨ B)。非门反转输入 (¬A)。与非门和或非门是通用门，因为任何逻辑函数都可以仅用与非门或仅用或非门构建。
Truth tables list all possible input combinations and their corresponding outputs. Boolean expressions can be simplified using Karnaugh maps or algebraic laws such as absorption, distribution and De Morgan’s laws: ¬(A ∧ B) = ¬A ∨ ¬B, ¬(A ∨ B) = ¬A ∧ ¬B.
真值表列出了所有可能的输入组合及其对应的输出。可以使用卡诺图或代数定律（吸收律、分配律和德摩根定律：¬(A ∧ B) = ¬A ∨ ¬B，¬(A ∨ B) = ¬A ∧ ¬B）来化简布尔表达式。
4. Processor Components & Fetch-Execute Cycle | 处理器组件与取指执行周期
The Central Processing Unit (CPU) contains the Control Unit (CU), Arithmetic Logic Unit (ALU), and registers. The CU decodes instructions and generates control signals; the ALU performs arithmetic and logical operations.
中央处理器包含控制器、算术逻辑单元和寄存器。控制器解码指令并产生控制信号；ALU 执行算术和逻辑运算。
Key registers: Program Counter (PC) holds the address of the next instruction; Memory Address Register (MAR) holds the address of data/instruction to be fetched; Memory Data Register (MDR) holds the data read from or written to memory; Current Instruction Register (CIR) holds the instruction being executed; Accumulator (ACC) stores intermediate results.
关键寄存器：程序计数器(PC)存放下一条指令地址；内存地址寄存器(MAR)存放待取数据/指令的地址；内存数据寄存器(MDR)存放从内存读取或写入的数据；当前指令寄存器(CIR)存放正在执行的指令；累加器(ACC)存储中间结果。
The fetch-decode-execute cycle repeats endlessly: Fetch – instruction pointed by PC is moved to CIR; PC is incremented. Decode – CU interprets the opcode. Execute – ALU performs operation, data may be read/written via MAR/MDR.
取指-解码-执行周期无限循环：取指——PC指向的指令移到CIR；PC递增。解码——CU解释操作码。执行——ALU执行操作，数据可能通过MAR/MDR读写。
5. Memory & Storage Hierarchy | 存储器与存储层次
Memory hierarchy balances speed, cost and capacity. Registers inside the CPU are fastest but smallest. Cache (L1, L2, L3) sits between CPU and RAM, storing frequently accessed data. RAM (Random Access Memory) is volatile main memory.
存储器层次结构平衡了速度、成本和容量。CPU内部的寄存器最快但最小。高速缓存（L1, L2, L3）位于CPU和RAM之间，存储频繁访问的数据。RAM（随机存取存储器）是易失性主存。
ROM (Read-Only Memory) is non-volatile and stores firmware or the BIOS. Virtual memory uses a portion of the hard drive as an extension of RAM when physical memory is full, but performance drops drastically due to much slower disk access.
ROM（只读存储器）是非易失性的，存储固件或 BIOS。虚拟内存在物理内存不足时将部分硬盘用作RAM扩展，但因磁盘访问慢得多而性能大幅下降。
Secondary storage: magnetic (HDD – high capacity, mechanical), optical (CD, DVD, Blu-ray), and solid-state (SSD – flash memory, faster, no moving parts, lower power). Cloud storage provides remote access but relies on internet connectivity.
辅助存储器：磁存储（HDD – 大容量，机械式）、光存储（CD、DVD、蓝光）和固态存储（SSD – 闪存，更快，无移动部件，低功耗）。云存储提供远程访问但依赖互联网连接。
6. Operating Systems & Utility Software | 操作系统与实用程序
An Operating System (OS) acts as an interface between user, applications and hardware. Core functions include process management, memory management, file system management, I/O management, and providing a user interface (GUI or command line).
操作系统充当用户、应用程序和硬件之间的接口。核心功能包括进程管理、内存管理、文件系统管理、I/O 管理以及提供用户界面（图形界面或命令行）。
Process scheduling algorithms: Round Robin (time slices), First Come First Served, Shortest Job First, and priority-based scheduling. Multitasking allows concurrent execution by rapid context switching.
进程调度算法：轮转调度（时间片）、先来先服务、最短作业优先和基于优先级的调度。多任务通过快速上下文切换实现并发执行。
Memory management uses paging and segmentation to allocate RAM to processes. Virtual memory, as described, extends capacity. Utility software includes antivirus, disk defragmenter, backup tools, compression software and firewalls.
内存管理使用分页和分段为进程分配RAM。虚拟内存如前所述扩展容量。实用程序软件包括防病毒软件、磁盘碎片整理程序、备份工具、压缩软件和防火墙。
7. Networks & Protocols | 网络与协议
Networks can be classified by scale: PAN (Personal), LAN (Local), MAN (Metropolitan), WAN (Wide). Topologies include star, bus, ring and mesh, each with trade-offs in reliability, cost and scalability.
网络可按规模分类：PAN（个人网）、LAN（局域网）、MAN（城域网）、WAN（广域网）。拓扑结构有星型、总线型、环型和网状型，各自在可靠性、成本和可扩展性方面各有权衡。
The TCP/IP model consists of four layers: Application (HTTP, FTP, SMTP), Transport (TCP, UDP), Internet (IP), and Network Access (Ethernet, Wi-Fi). Protocols define rules for communication. HTTP/HTTPS for web, FTP for file transfer, SMTP/POP3 for email.
TCP/IP 模型包含四层：应用层（HTTP、FTP、SMTP）、传输层（TCP、UDP）、网际层（IP）和网络接入层（以太网、Wi-Fi）。协议定义了通信规则。HTTP/HTTPS 用于万维网，FTP 用于文件传输，SMTP/POP3 用于电子邮件。
IP addressing: IPv4 uses 32-bit addresses (e.g., 192.168.1.1), while IPv6 uses 128-bit addresses to overcome exhaustion. Subnet masks split an IP address into network and host portions. DNS translates domain names to IP addresses.
IP 寻址：IPv4 使用 32 位地址（如 192.168.1.1），而 IPv6 使用 128 位地址以解决地址枯竭问题。子网掩码将 IP 地址分为网络部分和主机部分。DNS 将域名转换为 IP 地址。
8. Algorithms, Pseudocode & Tracing | 算法、伪代码与追踪
An algorithm is a step-by-step procedure to solve a problem. It must be unambiguous, finite and effective. Common ways to express algorithms: structured English, flowcharts and pseudocode.
算法是解决问题的分步过程，必须明确、有限且有效。表达算法的常见方式：结构化英语、流程图和伪代码。
Basic control structures: sequence, selection (IF…THEN…ELSE, CASE) and iteration (FOR, WHILE, REPEAT…UNTIL). Trace tables track variable values step-by-step to identify logic errors.
基本控制结构：顺序、选择（IF…THEN…ELSE，CASE）和迭代（FOR, WHILE, REPEAT…UNTIL）。追踪表逐步跟踪变量值以识别逻辑错误。
Sorting algorithms: Bubble Sort (compare adjacent, swap; O(n²)), Insertion Sort (build sorted sublist; O(n²)), Merge Sort (divide and conquer; O(n log n)). Searching: Linear Search (O(n)), Binary Search (O(log n), requires sorted array).
排序算法：冒泡排序（比较相邻元素，交换；O(n²)）、插入排序（构建已排序子列表；O(n²)）、归并排序（分治法；O(n log n)）。搜索：线性搜索（O(n)）、二分搜索（O(log n)，要求有序数组）。
Algorithm efficiency is measured by Big O notation, describing worst-case time/space complexity as input size n grows.
算法效率以大 O 表示法度量，描述随输入规模 n 增长的最坏情况时间/空间复杂度。
9. Data Structures — Arrays, Lists, Stacks, Queues, Trees | 数据结构——数组、链表、栈、队列、树
Arrays store elements of the same data type in contiguous memory locations, accessed via index with O(1) time for reading, but insertion/deletion O(n). 2D arrays are used for matrices and grids.
数组将相同数据类型的元素存储在连续内存位置，通过索引访问，读取 O(1)，但插入/删除 O(n)。二维数组用于矩阵和网格。
Linked lists consist of nodes with data and a pointer to the next node; dynamic size, efficient insertion/deletion O(1) at a known position, but slower index access O(n). Stacks follow LIFO (Last In First Out) with operations push(), pop(), peek().
链表由包含数据和指向下一节点指针的节点组成；动态大小，在已知位置插入/删除 O(1) 高效，但索引访问较慢 O(n)。栈遵循后进先出 (LIFO)，操作有 push()、pop()、peek()。
Queues are FIFO (First In First Out), with enqueue() and dequeue() operations; used in printer spooling and BFS. Binary trees have nodes with at most two children; Binary Search Tree (BST) maintains left < root < right for fast lookup O(log n) if balanced.
队列为先进先出 (FIFO)，有 enqueue() 和 dequeue() 操作；用于打印缓冲和广度优先搜索。二叉树节点最多有两个子节点；二叉搜索树 (BST) 保持左 < 根 < 右，若平衡可实现快速查找 O(log n)。
10. Databases & SQL | 数据库与 SQL
A relational database stores data in tables (relations) linked by primary keys and foreign keys. Each table consists of rows (records) and columns (fields). Normalisation reduces data redundancy and prevents update anomalies (1NF, 2NF, 3NF).
关系数据库将数据存储在通过主键和外键关联的表（关系）中。每张表由行（记录）和列（字段）组成。规范化减少数据冗余并防止更新异常（1NF、2NF、3NF）。
SQL (Structured Query Language) commands: SELECT columns FROM table WHERE condition; INSERT INTO table VALUES (…); UPDATE table SET col=val WHERE …; DELETE FROM … Use JOIN to combine tables on matching keys.
SQL 命令：SELECT columns FROM table WHERE condition; INSERT INTO table VALUES (…); UPDATE table SET col=val WHERE …; DELETE FROM … 使用 JOIN 基于匹配键合并表。
DBMS (Database Management System) provides security, concurrency control, backup and recovery. Data warehousing and data mining support business intelligence by analysing large datasets.
数据库管理系统 (DBMS) 提供安全性、并发控制、备份和恢复。数据仓库和数据挖掘通过分析大规模数据集支持商业智能。
11. Software Development Life Cycle & Methodologies | 软件开发生命周期与方法论
The Software Development Life Cycle (SDLC) typically includes: Feasibility study, Requirements analysis, Design, Implementation, Testing, Deployment and Maintenance. Each stage produces documentation to ensure clarity.
软件开发生命周期通常包括：可行性研究、需求分析、设计、实现、测试、部署和维护。每个阶段都产生文档以确保清晰。
Waterfall model follows a linear sequential approach, suitable for well-understood requirements. Agile methodologies (Scrum, XP) iterate in short sprints, embracing changing requirements and continuous feedback. Prototyping builds early mock-ups to validate user needs.
瀑布模型遵循线性顺序方法，适用于需求明确的项目。敏捷方法（Scrum、极限编程）在短迭代周期中开发，接纳需求变化和持续反馈。原型法构建早期模型以验证用户需求。
Testing strategies: black-box (functional, no knowledge of internals) vs white-box (structural, examines code logic). Alpha testing by developers, beta testing by end-users. Automated testing improves reliability in continuous integration.
测试策略：黑盒测试（功能测试，不了解内部）与白盒测试（结构测试，检查代码逻辑）。alpha 测试由开发者进行，beta 测试由最终用户进行。自动化测试在持续集成中提升可靠性。
12. Ethical, Legal & Environmental Impacts | 伦理、法律与环境影响
Data protection legislation (e.g., UK Data Protection Act / GDPR) regulates collection, storage and processing of personal data. It grants individuals rights to access, correct and delete their data. Organisations must obtain consent and ensure security.
数据保护立法（如英国《数据保护法》/GDPR）规范个人数据的采集、存储和处理。它赋予个人访问、更正和删除其数据的权利。组织必须获得同意并确保安全。
The Computer Misuse Act criminalises unauthorised access to systems, spreading malware, and hacking. Intellectual property rights protect software through copyright and patents. Digital divide refers to inequalities in access to technology based on socioeconomic, geographic or demographic factors.
《计算机滥用法》将未经授权访问系统、传播恶意软件和黑客行为定为刑事犯罪。知识产权通过版权和专利保护软件。数字鸿沟指因社会经济、地理或人口因素造成的技术访问不平等。
Environmental concerns: e-waste from discarded devices contains toxic materials; data centres consume vast electricity. Green IT aims to reduce carbon footprint through energy-efficient hardware, virtualisation and responsible recycling.
环境问题：废弃设备产生的电子垃圾含有有毒物质；数据中心消耗巨量电力。绿色 IT 旨在通过节能硬件、虚拟化和负责任回收减少碳足迹。
Professional codes of conduct (ACM, BCS) require integrity, confidentiality and public interest. Ethical dilemmas arise in areas like AI bias, surveillance, and autonomous decision-making.
专业行为准则（ACM、BCS）要求诚信、保密和维护公众利益。伦理困境出现在人工智能偏见、监控和自主决策等领域。
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