Pre-U Cambridge Computer Science: Core Knowledge Overview | Pre-U剑桥计算机：核心知识点梳理

📚 Pre-U Cambridge Computer Science: Core Knowledge Overview | Pre-U剑桥计算机：核心知识点梳理

This article summarises the essential topics covered in the Pre-U Computer Science syllabus, providing a structured revision guide for key concepts ranging from hardware architecture to computational thinking and ethical issues.

本文梳理 Pre-U 计算机科学课程的核心知识点，涵盖从硬件架构到计算思维及伦理问题的结构化复习指南。

---

1. Computer Architecture and Hardware | 计算机体系结构与硬件

The von Neumann architecture forms the foundation of most modern computers. It consists of a central processing unit (CPU), memory, input/output devices, and a system bus connecting them. The CPU itself contains the arithmetic logic unit (ALU), control unit (CU), and a set of registers such as the program counter (PC), memory address register (MAR), and memory data register (MDR).

冯·诺依曼体系结构是现代计算机的基础。它由中央处理器(CPU)、存储器、输入/输出设备以及连接它们的系统总线组成。CPU内部包含算术逻辑单元(ALU)、控制单元(CU)以及一组寄存器，如程序计数器(PC)、存储器地址寄存器(MAR)和存储器数据寄存器(MDR)。

The fetch-decode-execute cycle describes how the CPU processes instructions: the PC holds the address of the next instruction; the instruction is fetched into the current instruction register (CIR) via the MDR; the control unit decodes the opcode; then the ALU executes the instruction, and the result is stored. This cycle repeats continuously.

取指-译码-执行周期描述了CPU如何处理指令：PC保存下一条指令的地址；指令通过MDR被取出并存入当前指令寄存器(CIR)；控制单元对操作码进行译码；然后ALU执行指令，结果被存储。该周期不断重复。

Register | 寄存器	Function | 功能
PC (Program Counter)	Holds the address of the next instruction | 存放下一条指令地址
MAR	Stores the memory address to be accessed | 存放待访问的内存地址
MDR	Temporarily holds data from/to memory | 暂存来自/去向内存的数据
CIR	Stores the current instruction being executed | 存放当前执行的指令
ACC (Accumulator)	Holds results of ALU operations | 保存ALU运算结果

Memory hierarchy improves performance: registers are fastest but smallest, followed by cache (L1, L2, L3), main memory (RAM), and secondary storage (SSD/HDD). The principle of locality allows cache to store frequently accessed data, reducing the average memory access time.

存储层次提升性能：寄存器最快但容量最小，接着是缓存(L1, L2, L3)、主存(RAM)和辅助存储器(SSD/HDD)。局部性原理使得缓存可存储频繁访问的数据，从而降低平均内存访问时间。

---

2. Data Representation | 数据表示

Computers represent all data in binary (base-2). Unsigned integers can be directly converted; for example, 1011₂ = (1×2³)+(0×2²)+(1×2¹)+(1×2⁰) = 11₁₀. Hexadecimal (base-16) is often used as a more compact representation, where A–F correspond to 10–15.

计算机所有数据均以二进制(基数为2)表示。无符号整数可直接转换；例如1011₂ = (1×2³)+(0×2²)+(1×2¹)+(1×2⁰) = 11₁₀。十六进制(基数为16)常作为更紧凑的表示，A–F对应10–15。

Negative numbers can be represented using sign-and-magnitude, one’s complement, or two’s complement. Two’s complement is preferred because it eliminates duplicate zero and simplifies subtraction: to obtain -n, invert all bits of n and add 1. For an 8-bit number, the range is -128 to +127.

负数可用原码、反码或补码表示。补码最为常用，因为它消除了重复零并简化了减法：求 -n 时，将n的所有位取反再加1。8位补码范围是 -128 到 +127。

Characters are encoded using ASCII (7-bit or extended 8-bit) or Unicode (e.g., UTF-8). Floating-point numbers follow the IEEE 754 standard, stored as sign, exponent, and mantissa. For instance, 5.75₁₀ in binary is 101.11₂, normalised to 1.0111 × 2².

字符通过ASCII(7位或扩展8位)或Unicode(如UTF-8)进行编码。浮点数遵循IEEE 754标准，以符号、指数和尾数存储。例如5.75₁₀的二进制为101.11₂，规范化后是1.0111 × 2²。

Binary addition: 1101₂ + 0110₂ = 10011₂ (carry generated)

二进制加法：1101₂ + 0110₂ = 10011₂ (产生进位)

---

3. Operating Systems | 操作系统

An operating system (OS) acts as an intermediary between hardware and user applications. Its core functions include process management (scheduling, multitasking), memory management (paging, segmentation, virtual memory), file system management, and device handling via interrupts.

操作系统(OS)作为硬件与用户应用程序之间的中介。其核心功能包括进程管理(调度、多任务)、内存管理(分页、分段、虚拟内存)、文件系统管理以及通过中断进行设备处理。

Interrupts allow the CPU to respond to events such as I/O completion or errors. When an interrupt occurs, the current process state is saved, the interrupt service routine (ISR) is executed, and then the previous state is restored. This enables efficient I/O operations without busy waiting.

中断使得CPU能够响应I/O完成或错误等事件。中断发生时，当前进程状态被保存，执行中断服务例程(ISR)，然后恢复先前状态。这实现了高效的I/O操作而无需忙等待。

Common scheduling algorithms include First Come First Served (FCFS), Shortest Job First (SJF), Round Robin (RR), and priority-based scheduling. The choice affects throughput, turnaround time, and response time. Multitasking operating systems use time-slicing to give the illusion of concurrent execution.

常见的调度算法包括先来先服务(FCFS)、最短作业优先(SJF)、轮转调度(RR)和基于优先级的调度。选择何种算法影响吞吐量、周转时间和响应时间。多任务操作系统利用时间片轮转营造并发执行的假象。

---

4. Networks and Communication | 网络与通信

Networks can be classified by scale: Local Area Network (LAN) covers a small geographic area, often using Ethernet or Wi-Fi; Wide Area Network (WAN) spans large distances, typically employing leased lines or MPLS. The Internet is the global network of networks, using the TCP/IP protocol suite.

网络可按规模分类：局域网(LAN)覆盖较小地理范围，常使用以太网或Wi-Fi；广域网(WAN)跨越大面积区域，通常使用专线或MPLS。互联网是全球网络之网络，采用TCP/IP协议族。

The OSI model provides a conceptual framework with seven layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application. In practice, the TCP/IP model condenses these into four layers: Link, Internet, Transport, and Application. Each layer adds its own header to the data.

OSI模型提供了概念框架，共七层：物理层、数据链路层、网络层、传输层、会话层、表示层和应用层。实际中TCP/IP模型将其精简为四层：链路层、互联网层、传输层和应用层。每一层都添加自己的头部到数据。

IP addresses (IPv4: 32-bit, dotted decimal; IPv6: 128-bit, hexadecimal) identify devices on a network. Subnetting divides a network into smaller segments. The TCP protocol provides reliable, connection-oriented delivery with error checking and flow control, while UDP offers connectionless, faster transmission.

IP地址(IPv4: 32位, 点分十进制; IPv6: 128位, 十六进制)标识网络上的设备。子网划分将网络分割为更小的网段。TCP协议提供可靠、面向连接的传输及错误检查和流量控制，而UDP提供无连接、更快的传输。

• Common protocols: HTTP/HTTPS (web), FTP (file transfer), SMTP (email), DNS (name resolution)
• 常见协议：HTTP/HTTPS(网页)、FTP(文件传输)、SMTP(电子邮件)、DNS(域名解析)

---

5. Programming Fundamentals | 编程基础

Variables and data types are the building blocks of any program. Primitive types include integer, float (real), character, Boolean, and string. Composite types such as arrays, records, and lists allow grouping of related data. Strong typing enforces type checking at compile-time, whereas dynamic typing checks at run-time.

变量和数据类型是任何程序的基石。基本类型包括整数、浮点数(实数)、字符、布尔和字符串。复合类型如数组、记录和列表允许将相关数据组织在一起。强类型在编译时进行类型检查，而动态类型在运行时检查。

Control structures direct program flow: sequence, selection (if-else, switch-case), and iteration (for, while, do-while loops). Subroutines (procedures and functions) encapsulate reusable code. Parameters can be passed by value (a copy) or by reference (the original variable).

控制结构引导程序流：顺序、选择(if-else, switch-case)和迭代(for, while, do-while循环)。子程序(过程和函数)封装可重用代码。参数可按值传递(传递副本)或按引用传递(传递原变量)。

Scope defines the visibility of variables: local variables are accessible only within the subroutine where they are declared; global variables exist for the entire program. Recursion is a technique where a function calls itself, requiring a base case to terminate; the call stack holds each invocation’s state.

作用域定义变量的可见性：局部变量仅在其声明的子程序内可访问；全局变量在整个程序中都存在。递归是一种函数调用自身的技术，必须包含终止的基准情形；调用栈保存每次调用的状态。

---

6. Algorithms and Data Structures | 算法与数据结构

Searching algorithms: linear search examines each element sequentially until the target is found or the list ends, with O(n) time complexity. Binary search requires a sorted array, repeatedly dividing the search interval in half, achieving O(log n) time. Sorting algorithms include bubble sort (O(n²)), insertion sort (O(n²)), and merge sort (O(n log n)).

查找算法：线性查找依次检查每个元素直到找到目标或列表末尾，时间复杂度为O(n)。二分查找要求有序数组，不断将查找区间减半，时间复杂度为O(log n)。排序算法包括冒泡排序(O(n²))、插入排序(O(n²))和归并排序(O(n log n))。

Abstract data types (ADTs): a stack follows Last In First Out (LIFO) with operations push, pop, and peek. A queue uses First In First Out (FIFO) with enqueue and dequeue. A linked list consists of nodes, each containing data and a pointer to the next node, allowing efficient insertion and deletion.

抽象数据类型(ADT)：栈遵循后进先出(LIFO)，操作有push、pop和peek。队列使用先进先出(FIFO)，操作为enqueue和dequeue。链表由节点组成，每个节点包含数据和一个指向下一节点的指针，从而支持高效的插入与删除。

Trees are hierarchical structures. A binary tree has at most two children per node. A binary search tree (BST) maintains the property: left subtree values < node < right subtree values. Graphs can be represented using adjacency matrices or adjacency lists, and traversed via depth-first search (DFS) or breadth-first search (BFS).

树是层次结构。二叉树每个节点最多有两个子节点。二叉搜索树(BST)维持如下性质：左子树值 < 节点值 < 右子树值。图可用邻接矩阵或邻接表表示，并通过深度优先搜索(DFS)或广度优先搜索(BFS)进行遍历。

---

7. Databases and SQL | 数据库与SQL

A relational database organises data into tables (relations), where each row (tuple) represents a record and each column an attribute. A primary key uniquely identifies each row; foreign keys establish relationships between tables. Normalisation (1NF, 2NF, 3NF) reduces data redundancy and anomalies by decomposing tables.

关系数据库将数据组织成表(关系)，每行(元组)表示一条记录，每列表示属性。主键唯一标识每一行；外键建立表间关系。规范化(1NF, 2NF, 3NF)通过分解表来减少数据冗余和异常。

SQL (Structured Query Language) is used to define and manipulate data. The SELECT statement retrieves data: SELECT column1, column2 FROM table WHERE condition;. Other commands include INSERT, UPDATE, DELETE, and JOIN operations (INNER, LEFT, RIGHT) to combine tables.

SQL(结构化查询语言)用于定义和操作数据。SELECT语句检索数据：SELECT column1, column2 FROM table WHERE condition;。其他命令包括INSERT、UPDATE、DELETE，以及用于合并表的JOIN操作(INNER, LEFT, RIGHT)。

Entity-Relationship (ER) diagrams model data with entities, attributes, and relationships (1:1, 1:M, M:N). A many-to-many relationship must be resolved into a linking table. ACID properties (Atomicity, Consistency, Isolation, Durability) ensure reliable transaction processing.

实体关系(ER)图用实体、属性和关系(1:1, 1:M, M:N)来建模数据。多对多关系必须转换为链接表。ACID特性(原子性、一致性、隔离性、持久性)确保可靠的事务处理。

---

8. Computer Security | 计算机安全

Security threats include malware (viruses, worms, trojans), phishing, denial-of-service (DoS) attacks, and man-in-the-middle attacks. A virus attaches itself to legitimate programs, while a worm spreads independently across networks. Phishing uses deceptive emails to trick users into revealing sensitive information.

安全威胁包括恶意软件(病毒、蠕虫、木马)、钓鱼攻击、拒绝服务攻击(DoS)和中间人攻击。病毒依附于合法程序传播，蠕虫则可独立在网络中扩散。钓鱼攻击使用欺骗性邮件诱导用户泄露敏感信息。

Defensive measures involve firewalls, which filter incoming and outgoing traffic based on rules; encryption, which scrambles data using algorithms; and intrusion detection systems (IDS). Symmetric encryption (e.g., AES) uses the same key for encryption and decryption, whereas asymmetric encryption (e.g., RSA) employs a public/private key pair.

防御措施包括防火墙(根据规则过滤进出流量)、加密(使用算法加扰数据)以及入侵检测系统(IDS)。对称加密(如AES)使用相同密钥进行加解密，而非对称加密(如RSA)使用公钥/私钥对。

Regular software updates, strong password policies, and user education are critical. Digital signatures and certificates provide authentication and non-repudiation. A hash function (e.g., SHA-256) produces a fixed-size digest to verify data integrity.

定期软件更新、强密码策略和用户教育至关重要。数字签名和数字证书提供认证和不可否认性。哈希函数(如SHA-256)生成固定长度的摘要以验证数据完整性。

---

9. Boolean Algebra and Logic Circuits | 布尔代数与逻辑电路

Boolean algebra operates on binary values with operators: AND (∧), OR (∨), and NOT (¬). Laws include commutative, associative, distributive, identity, and de Morgan’s laws, e.g., ¬(A ∧ B) = ¬A ∨ ¬B. Boolean expressions can be simplified using these laws or Karnaugh maps (K-maps).

布尔代数在二进制值上进行操作，运算符包括与(∧)、或(∨)和非(¬)。定律有交换律、结合律、分配律、恒等律和德摩根定律，例如¬(A ∧ B) = ¬A ∨ ¬B。布尔表达式可使用这些定律或卡诺图进行化简。

De Morgan’s Law: ¬(A ∧ B) = ¬A ∨ ¬B

德摩根定律：¬(A ∧ B) = ¬A ∨ ¬B

Logic gates are physical implementations: AND, OR, NOT, NAND, NOR, XOR, XNOR. Circuits can be built using only NAND or NOR gates, as they are functionally complete. Truth tables map all input combinations to outputs and are used to verify logic.

逻辑门是物理实现：与门、或门、非门、与非门、或非门、异或门、同或门。由于与非门和或非门功能完备，电路可仅用它们构建。真值表列出所有输入组合对应的输出，用于验证逻辑。

A half adder adds two bits, producing a sum (S = A XOR B) and a carry (C = A AND B). A full adder also includes a carry-in input. Multi-bit adders can be cascaded. Flip-flops, built from gates, form the basis of memory and sequential circuits.

半加器对两个比特做加法，产生和(S = A XOR B)与进位(C = A AND B)。全加器还包含进位输入。多比特加法器可以级联。由门电路构成的触发器是存储器和时序电路的基础。

---

10. Computational Thinking and Software Engineering | 计算思维与软件工程

Computational thinking involves decomposition (breaking a problem into smaller parts), pattern recognition (identifying similarities), abstraction (focusing on essential details), and algorithmic design (creating step-by-step solutions). These skills apply across disciplines to produce efficient solutions.

计算思维包括分解(将问题拆解为更小部分)、模式识别(识别相似之处)、抽象(聚焦于关键细节)和算法设计(创建逐步解决方案)。这些技能可跨学科应用以生成高效解法。

Software development life cycle (SDLC) models include the waterfall model (linear phases: analysis, design, implementation, testing, maintenance) and agile methodologies (iterative, with frequent feedback). Testing is essential; types include unit testing, integration testing, and acceptance testing. Debugging techniques include dry running and trace tables.

软件开发生命周期(SDLC)模型包括瀑布模型(线性阶段：分析、设计、实现、测试、维护)和敏捷方法(迭代式，并伴有频繁反馈)。测试至关重要；类型包括单元测试、集成测试和验收测试。调试技术包括脑跑和跟踪表。

Version control systems (e.g., Git) track changes and facilitate collaboration. Good code documentation and adherence to coding standards improve maintainability. The use of modular design and reusable components reduces complexity and errors.

版本控制系统(如Git)跟踪变更并促进协作。良好的代码文档和遵守编码规范可提升可维护性。采用模块化设计和可复用组件可降低复杂性和错误率。

---

11. Ethical, Legal and Environmental Issues | 道德、法律与环境问题

Computing professionals must consider ethical issues such as privacy, data protection, and accessibility. Legislation like the GDPR (General Data Protection Regulation) in the EU governs how personal data must be collected, stored, and processed, giving individuals rights over their data.

计算机专业人士必须考量隐私、数据保护和可访问性等伦理问题。诸如欧盟的GDPR(通用数据保护条例)等法律规定了个人数据的收集、存储和处理方式，赋予个人对其数据的权利。

The Computer Misuse Act criminalises unauthorised access, modification, and use of computer material. Intellectual property rights protect software through copyright and patents. Plagiarism and piracy remain serious concerns in the digital environment.

《计算机滥用法》将未经授权的访问、修改和使用计算机材料定为刑事犯罪。知识产权通过版权和专利保护软件。剽窃和盗版仍是数字环境中的重大问题。

Environmental impact: the production, use, and disposal of computing devices consume energy and generate e-waste. Energy-efficient hardware, virtualisation, and responsible recycling help mitigate these effects. The digital divide refers to the gap between those with access to technology and those without, raising social equity considerations.

环境影响：计算设备的生产、使用和废弃消耗能源并产生电子垃圾。节能硬件、虚拟化和负责任回收有助于缓解这些影响。数字鸿沟指拥有科技资源的人群与无法获取者之间的差距，引发社会公平考量。

---

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

更多咨询请联系16621398022（同微信）