IB & CCEA Computer Science: Last-Minute Revision Notes | IB 与 CCEA 计算机：考前冲刺笔记

📚 IB & CCEA Computer Science: Last-Minute Revision Notes | IB 与 CCEA 计算机：考前冲刺笔记

This revision guide condenses the most critical topics from the IB Diploma and CCEA GCE Computer Science specifications into clear, bilingual summary notes. Use it to reinforce your understanding of core concepts, common algorithms, data representation, networking, and ethical considerations just before the exam.

本复习指南将 IB 文凭与 CCEA GCE 计算机科学课程中最关键的主题浓缩为清晰的双语摘要笔记。在考前几天使用它来巩固你对核心概念、常见算法、数据表示、网络和伦理考量的理解。

1. Data Representation | 数据表示

All data inside a computer is stored in binary. The smallest unit is a bit (0 or 1), 8 bits form a byte. Numbers can be represented as unsigned binary, two’s complement for signed integers, or floating‑point for real numbers following the IEEE 754 standard.

计算机内所有数据都以二进制存储。最小单位是比特（0 或 1），8 比特组成一个字节。数字可以表示为无符号二进制、用补码表示有符号整数，或按照 IEEE 754 标准的浮点数表示实数。

When converting a negative denary number to two’s complement, write the positive magnitude in binary, invert the bits (‘flip’), and add 1. For floating point, remember the structure: [sign bit] [exponent] [mantissa]. The number = (-1)^sign × 1.mantissa × 2^{exponent−bias}.

将负十进制数转换为补码时，写出正数的二进制形式，将所有位取反（“翻转”）再加 1。浮点数记住结构：[符号位] [指数] [尾数]。数值 = (-1)^符号 × 1.尾数 × 2^{指数−偏移量}。

Characters are encoded using ASCII (7‑bit) or Unicode (UTF‑8, UTF‑16). Images use bit‑map (pixel arrays with colour depth) or vector graphics (mathematical descriptions). Sound is sampled at a given sample rate and bit depth; higher values improve quality but increase file size.

字符使用 ASCII（7 位）或 Unicode（UTF‑8、UTF‑16）编码。图像使用位图（具有颜色深度的像素阵列）或矢量图形（数学描述）。声音按给定的采样率和位深度采样；更高的值提高质量但增加文件大小。

Key units: kilo (10³ or 2¹⁰ in computing), mega (10⁶ or 2²⁰), giga, tera. Always check context for decimal vs binary prefixes (kB vs KiB).

关键单位：千（十进制 10³ 或计算机中的 2¹⁰）、兆（10⁶ 或 2²⁰）、吉、太。始终检查上下文是十进制还是二进制前缀（kB 与 KiB）。

2. Computer Architecture | 计算机体系结构

The Von Neumann architecture stores both instructions and data in the same memory. Key components include the CPU (with ALU, CU, and registers), RAM (main memory), and I/O controllers connected via buses (data, address, control).

冯·诺依曼体系结构将指令和数据存储在同一内存中。关键组件包括 CPU（含有 ALU、CU 和寄存器）、RAM（主存）和通过总线（数据总线、地址总线、控制总线）连接的 I/O 控制器。

The fetch‑decode‑execute cycle: PC (program counter) holds address of next instruction; it is copied to MAR, instruction fetched from memory into MDR, then decoded by CU, and executed (e.g., ALU operation, memory access).

取指−译码−执行周期：PC（程序计数器）保存下一条指令的地址；它被复制到 MAR，从内存中取出指令放入 MDR，然后由 CU 译码，并执行（如 ALU 操作、内存访问）。

Factors affecting CPU performance: clock speed (GHz), number of cores, cache size (L1/L2/L3). Pipelining allows overlapping of fetch‑decode‑execute stages, improving throughput.

影响 CPU 性能的因素：时钟速度（GHz）、核心数量、缓存大小（L1/L2/L3）。流水线技术允许取指、译码、执行阶段重叠，提高吞吐量。

Secondary storage: magnetic (HDD), solid state (SSD), optical. SSDs are faster, more durable but costlier per GB. RAID levels provide redundancy and performance.

辅助存储：磁储存（HDD）、固态（SSD）、光盘。SSD 速度更快、更耐用，但每 GB 成本更高。RAID 级别提供冗余和性能。

3. Operating Systems & Resource Management | 操作系统与资源管理

The OS manages hardware, provides a user interface, and enables multitasking. It handles process scheduling (round‑robin, priority‑based, multi‑level feedback queue), memory management (paging, segmentation, virtual memory), and file systems.

操作系统管理硬件、提供用户界面并支持多任务。它处理进程调度（轮转、基于优先级、多级反馈队列）、内存管理（分页、分段、虚拟内存）和文件系统。

Virtual memory uses disk space as an extension of RAM, swapping pages in and out. This allows running large programs but can cause thrashing if the working set exceeds available RAM.

虚拟内存使用磁盘空间作为 RAM 的扩展，将页面换入换出。这允许运行大型程序，但如果工作集超过可用 RAM 则会导致系统颠簸（thrashing）。

Interrupts are signals that alert the CPU to high‑priority events (e.g., I/O completion, errors). The CPU saves its state, runs an interrupt service routine (ISR), then resumes.

中断是提醒 CPU 处理高优先级事件的信号（如 I/O 完成、错误）。CPU 保存其状态，运行中断服务程序（ISR），然后恢复。

4. Networks & Data Transmission | 网络与数据传输

Networks can be classified by scale (LAN, WAN) and topology (star, bus, mesh). Protocols define rules for communication; the TCP/IP stack includes application, transport, internet, and link layers.

网络可按规模（局域网、广域网）和拓扑结构（星形、总线、网状）分类。协议定义通信规则；TCP/IP 协议栈包括应用层、传输层、互联网层和链路层。

Key protocols: HTTP/HTTPS (web), FTP (file transfer), SMTP/POP3 (email), TCP (reliable, connection‑oriented), UDP (fast, connectionless), IP (addressing). IPv4 uses 32‑bit addresses, IPv6 uses 128‑bit.

关键协议：HTTP/HTTPS（网页）、FTP（文件传输）、SMTP/POP3（电子邮件）、TCP（可靠的面向连接）、UDP（快速无连接）、IP（寻址）。IPv4 使用 32 位地址，IPv6 使用 128 位。

Packet switching breaks data into packets, sent independently and reassembled. Circuit switching establishes a dedicated path. Security: firewalls, encryption (symmetric/asymmetric), and digital signatures.

分组交换将数据拆分为数据包，独立发送并重组。电路交换建立专用路径。网络安全：防火墙、加密（对称/非对称）和数字签名。

5. Databases & SQL | 数据库与 SQL

A relational database organises data into tables with rows (records) and columns (fields). Primary keys uniquely identify rows; foreign keys link tables. Normalisation (1NF, 2NF, 3NF) reduces redundancy and anomalies.

关系型数据库将数据组织成具有行（记录）和列（字段）的表。主键唯一标识行；外键连接表。规范化（1NF、2NF、3NF）减少冗余和异常。

SQL commands: SELECT, FROM, WHERE, ORDER BY, GROUP BY, INNER JOIN. Example: SELECT name, age FROM student WHERE grade = ‘A’ ORDER BY name;

SQL 命令：SELECT、FROM、WHERE、ORDER BY、GROUP BY、INNER JOIN。示例：SELECT name, age FROM student WHERE grade = ‘A’ ORDER BY name;

ACID properties (Atomicity, Consistency, Isolation, Durability) ensure reliable transactions. DBMS handles concurrency via locking.

ACID 属性（原子性、一致性、隔离性、持久性）保证事务可靠。DBMS 通过锁定处理并发。

6. Algorithms & Complexity | 算法与复杂度

Searching: linear search (O(n)) checks each element; binary search (O(log n)) requires sorted data. Sorting: bubble sort (O(n²)), insertion sort (O(n²) but efficient for small n), merge sort (O(n log n) stable), quicksort (O(n log n) average, O(n²) worst case).

搜索：线性搜索（O(n)）检查每个元素；二分搜索（O(log n)）需要排序数据。排序：冒泡排序（O(n²)）、插入排序（O(n²) 但对小 n 高效）、归并排序（O(n log n) 稳定）、快速排序（平均 O(n log n)、最坏 O(n²)）。

Big‑O notation describes upper bound time/space complexity. Understand recursion: base case + recursive call. Stack overflow occurs without a proper base case.

大 O 记号描述时间/空间复杂度的上界。理解递归：基准情形 + 递归调用。缺少合适的基准情形会导致栈溢出。

Graph traversal: depth‑first (DFS) uses stack, breadth‑first (BFS) uses queue. Dijkstra’s algorithm finds shortest path in weighted graphs with non‑negative edges.

图遍历：深度优先（DFS）使用栈，广度优先（BFS）使用队列。Dijkstra 算法在非负权重的图中寻找最短路径。

7. Programming Concepts | 编程概念

Variables, data types (integer, real, boolean, char, string), operators (+, -, *, /, MOD, DIV). Control structures: sequence, selection (IF‑THEN‑ELSE, CASE/SWITCH), iteration (FOR, WHILE, REPEAT‑UNTIL).

变量、数据类型（整数、实数、布尔、字符、字符串）、运算符（+、-、*、/、MOD、DIV）。控制结构：顺序、选择（IF‑THEN‑ELSE、CASE/SWITCH）、循环（FOR、WHILE、REPEAT‑UNTIL）。

Subroutines: procedures (perform actions) and functions (return values). Parameters can be passed by value (copy) or by reference (address). Recursion is a function calling itself.

子程序：过程（执行动作）和函数（返回值）。参数可以按值传递（副本）或按引用传递（地址）。递归是函数调用自身。

Object‑oriented programming (OOP) concepts: class, object, encapsulation, inheritance, polymorphism. A class defines attributes and methods; objects are instances.

面向对象编程（OOP）概念：类、对象、封装、继承、多态。类定义属性和方法；对象是实例。

8. Data Structures | 数据结构

Arrays: fixed size, contiguous memory, O(1) access. Linked lists: dynamic, nodes with data and pointer; insertion/deletion O(1) at head, O(n) for arbitrary position. Stacks (LIFO) and queues (FIFO) can be implemented with arrays or linked lists.

数组：固定大小、连续内存、O(1) 访问。链表：动态，结点含数据和指针；在头部插入/删除 O(1)，任意位置 O(n)。栈（后进先出）和队列（先进先出）可用数组或链表实现。

Trees: binary tree, binary search tree (BST left < root < right). Balanced BST (AVL, red‑black) gives O(log n) operations. Hash tables map keys to indices via hash function; collisions resolved by chaining or open addressing.

树：二叉树、二叉搜索树（BST 左 < 根 < 右）。平衡 BST（AVL、红黑树）提供 O(log n) 操作。哈希表通过哈希函数将键映射到索引；冲突由链地址法或开放寻址法解决。

9. System Development Life Cycle | 系统开发生命周期

Stages: feasibility study, analysis (requirements gathering, DFDs, use cases), design (flowcharts, pseudocode, data dictionaries), implementation, testing (alpha/beta, black/white box), deployment, maintenance.

阶段：可行性研究、分析（需求收集、数据流图、用例）、设计（流程图、伪代码、数据字典）、实施、测试（阿尔法/贝塔、黑盒/白盒）、部署、维护。

Changeover methods: direct, parallel, phased, pilot. Each has risks and benefits. Documentation includes user manuals and technical guides.

转换方法：直接、并行、分阶段、试点。每种都有风险和优点。文档包括用户手册和技术指南。

Prototyping and agile methodologies (e.g., Scrum) focus on iterative development and user feedback, contrasting with the waterfall model.

原型设计和敏捷方法（如 Scrum）注重迭代开发和用户反馈，与瀑布模型形成对比。

10. Ethical & Legal Issues | 伦理与法律问题

Computer misuse: hacking, malware, phishing. Data protection laws (e.g., GDPR) regulate collection, storage, and processing of personal data. Copyright and software licensing (proprietary, open source, freeware) protect intellectual property.

计算机滥用：黑客攻击、恶意软件、网络钓鱼。数据保护法律（如 GDPR）规范个人数据的收集、存储和处理。版权和软件许可证（专有、开源、免费软件）保护知识产权。

Artificial intelligence and automation raise concerns about bias, accountability, and job displacement. Environmental impact: e‑waste, energy consumption of data centres. Ethical design should consider accessibility, inclusion, and sustainability.

人工智能和自动化引发了有关偏见、问责和就业替代的担忧。环境影响：电子废弃物、数据中心能耗。道德设计应考虑可访问性、包容性和可持续性。

Cybersecurity principles: confidentiality, integrity, availability (CIA triad). Regular backups, strong authentication, and staff training reduce risks.

网络安全原则：保密性、完整性、可用性（CIA 三要素）。定期备份、强身份验证和员工培训可降低风险。

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IB & CCEA Computer Science: Last-Minute Revision Notes | IB 与 CCEA 计算机：考前冲刺笔记