📚 Year 11 Cambridge Computer Science: Core Knowledge Review | Year 11 剑桥计算机：核心知识点梳理
This article provides a thorough review of the essential topics in the Year 11 Cambridge IGCSE Computer Science syllabus. It is designed to help you consolidate your understanding, covering number systems, data representation, hardware, software, networks, databases, and the wider ethical implications of computing. Each section presents a key concept in both English and Chinese, making it easy to follow and revise.
本文全面梳理了 Year 11 剑桥 IGCSE 计算机课程的核心知识点，旨在帮助你巩固理解，涵盖数制、数据表示、硬件、软件、网络、数据库以及更广泛的计算机伦理影响。每个部分均以中英双语呈现关键概念，便于学习和复习。
1. Number Systems & Data Representation | 数制与数据表示
Computers use binary (base‑2) to represent all data, as each storage unit can only hold two states. Denary (base‑10) numbers are converted to binary by successive division by 2, and to hexadecimal (base‑16) for a more compact representation. Each hex digit corresponds to a nibble (4 bits). Understanding how to convert between binary, denary, and hexadecimal is fundamental to computer science.
计算机使用二进制（基数为 2）表示所有数据，因为每个存储单元只能有两种状态。十进制（基数为 10）数通过不断除以 2 转换为二进制，而十六进制（基数为 16）则提供更紧凑的表示。每个十六进制数字对应一个半字节（4 位）。掌握二进制、十进制与十六进制之间的转换是计算机科学的基础。
Key conversion methods: For binary to denary, add the place values (1, 2, 4, 8, …) where the bit is 1. For denary to binary, repeatedly divide by 2, reading the remainders backwards. For hex to binary, convert each hex digit to its 4‑bit binary equivalent.
关键转换方法：二进制转十进制，将位值为 1 的位权（1, 2, 4, 8, …）相加。十进制转二进制，反复除以 2，反向读取余数。十六进制转二进制，将每个十六进制数字转换为对应的 4 位二进制数。
2. Binary Arithmetic & Overflow | 二进制运算与溢出
Binary addition follows the same rules as denary addition, carrying 1 to the next column when the sum exceeds 1. However, when the result of an addition requires more bits than the allocated word length, an overflow error occurs. Overflow is a common programming pitfall, especially in limited‑bit systems, and can lead to unexpected results or security holes.
二进制加法遵循与十进制加法相同的规则，当和超过 1 时向高位进 1。但是，当加法结果所需的位数超出分配的字长时，就会发生溢出错误。溢出是编程中常见的陷阱，尤其在位宽有限的系统中，可能导致意外结果或安全漏洞。
Shift operations: A logical shift left multiplies a binary number by 2 for each shift; a logical shift right divides by 2, discarding the least significant bit. Shifts are an efficient way to perform multiplication and division in low‑level code.
移位操作：逻辑左移每移一位将二进制数乘以 2；逻辑右移除以 2 并丢弃最低有效位。移位是低级代码中执行乘法和除法的高效方式。
3. Text, Sound & Image Representation | 文本、声音与图像表示
Text is stored using character sets. ASCII uses 7 bits (extended ASCII 8 bits) to represent 128 (or 256) characters, while Unicode uses up to 32 bits to cover virtually all writing systems and emojis. The choice of character set affects file size and compatibility.
文本使用字符集存储。ASCII 使用 7 位（扩展 ASCII 8 位）表示 128（或 256）个字符，而 Unicode 最多使用 32 位以覆盖几乎所有书写系统和表情符号。字符集的选择会影响文件大小和兼容性。
Sound is analogue and must be digitised by sampling. The sampling rate (samples per second) and bit depth determine the quality and file size. A higher sampling rate captures more detail, but increases the data volume. Images are represented as a grid of pixels, each assigned a colour value. Resolution (pixels per inch) and colour depth (bits per pixel) control clarity and file size.
声音是模拟信号，必须通过采样数字化。采样率（每秒采样次数）和位深度决定了音质和文件大小。更高的采样率能捕捉更多细节，但也会增加数据量。图像表示为像素网格，每个像素分配一个颜色值。分辨率（每英寸像素数）和颜色深度（每像素位数）影响清晰度和文件大小。
4. Data Transmission & Error Detection | 数据传输与错误检测
Data can be transmitted serially (one bit at a time) or in parallel (multiple bits simultaneously). Serial transmission is more common over long distances due to fewer synchronisation issues. Simplex, half‑duplex, and full‑duplex define the directionality of data flow.
数据可以串行（一次一位）或并行（同时多位）传输。串行传输因同步问题较少，在长距离中更常用。单工、半双工和全双工定义了数据流动的方向性。
To detect errors introduced during transmission, several methods are used. Parity checking adds a parity bit to make the number of 1s even (even parity) or odd. A checksum is a numerical sum of data blocks that is recalculated at the receiving end. Echo checks send data back to the sender for comparison, while Automatic Repeat reQuest (ARQ) uses acknowledgements and timeouts to ensure reliable delivery.
为检测传输中引入的错误，使用了多种方法。奇偶校验添加一个校验位，使 1 的个数为偶数（偶校验）或奇数。校验和是数据块的数值总和，在接收端重新计算。回波校验将数据发回发送方进行比较，而自动重传请求（ARQ）使用确认和超时机制确保可靠交付。
5. Encryption & Security | 加密与安全
Encryption protects data confidentiality by scrambling it into an unreadable form. Symmetric encryption uses a single key for both encryption and decryption, making it fast but requiring a secure key exchange. Asymmetric encryption (public‑key) uses a pair of keys: a public key for encryption and a private key for decryption, solving the key distribution problem.
加密通过将数据打乱为不可读的形式来保护数据的机密性。对称加密使用同一密钥进行加密和解密，速度较快，但需要安全的密钥交换。非对称加密（公钥加密）使用一对密钥：公钥用于加密，私钥用于解密，解决了密钥分发问题。
Security threats such as malware, phishing, and brute‑force attacks exploit vulnerabilities. Defences include firewalls, antivirus software, strong passwords, and two‑factor authentication. Understanding these concepts is essential for safeguarding digital systems.
安全威胁如恶意软件、网络钓鱼和暴力破解攻击会利用漏洞。防御措施包括防火墙、防病毒软件、强密码和双因素认证。理解这些概念对于保护数字系统至关重要。
6. Logic Gates & Circuits | 逻辑门与电路
Logic gates are the building blocks of digital circuits. The basic gates include AND, OR, NOT, NAND, NOR, and XOR. Each gate has a defined truth table showing the output for every combination of inputs. NAND and NOR are known as universal gates because any other gate can be constructed from them.
逻辑门是数字电路的构建模块。基本门包括 AND、OR、NOT、NAND、NOR 和 XOR。每个门都有定义好的真值表，显示每种输入组合下的输出。NAND 和 NOR 被称为通用门，因为可以用它们构造出任何其他门。
A simple logic circuit combines multiple gates to perform a desired logical function. You should be able to draw a circuit for a given logic expression, write a logic expression from a circuit, and complete a truth table. Real‑world examples include automatic night lamps and calculators.
一个简单的逻辑电路组合了多个门，以执行所需的逻辑功能。你应能根据给定的逻辑表达式绘制电路，从电路写出逻辑表达式，并填充真值表。现实中的例子包括自动夜灯和计算器。
| Gate | Symbol | Truth Table Summary |
|---|---|---|
| AND | A.B | Output 1 only if all inputs are 1 |
| OR | A+B | Output 1 if at least one input is 1 |
| NOT | ¬A | Outputs the inverse of the input |
| XOR | A⊕B | Output 1 if inputs are different |
7. Computer Architecture (CPU) | 计算机体系结构（CPU）
The Central Processing Unit (CPU) follows the fetch‑decode‑execute cycle. It consists of the Control Unit (CU), Arithmetic Logic Unit (ALU), and registers. Key registers include the Program Counter (PC), Memory Address Register (MAR), Memory Data Register (MDR), and Accumulator (ACC). The von Neumann architecture stores both data and instructions in the same memory.
中央处理器（CPU）遵循取指–解码–执行周期。它由控制单元（CU）、算术逻辑单元（ALU）和寄存器组成。关键寄存器包括程序计数器（PC）、存储器地址寄存器（MAR）、存储器数据寄存器（MDR）和累加器（ACC）。冯·诺依曼架构将数据和指令存储在同一内存中。
CPU performance is affected by clock speed (cycles per second), number of cores, and cache size. Cache is high‑speed memory close to the CPU that stores frequently used data and instructions. Increasing any of these factors generally improves performance, though thermal and power limitations exist.
CPU 性能受时钟频率（每秒周期数）、核心数量和缓存大小的影响。缓存是靠近 CPU 的高速存储器，用于存储频繁使用的数据和指令。增大这些因素通常能提高性能，但存在散热和功耗的限制。
8. Memory & Storage | 存储器与存储设备
Primary memory includes RAM (volatile, working memory) and ROM (non‑volatile, stores boot instructions). Secondary storage is used for long‑term data retention and comes in three main types: magnetic (HDD), optical (CD/DVD), and solid‑state (SSD, USB flash drives). Each has trade‑offs in capacity, speed, portability, and durability.
主存储器包括 RAM（易失性，工作内存）和 ROM（非易失性，存储启动指令）。辅助存储器用于长期数据保存，主要有三种类型：磁存储（HDD）、光存储（CD/DVD）和固态存储（SSD、USB 闪存盘）。它们在容量、速度、便携性和耐用性上各有取舍。
Solid‑state storage is faster and more shock‑resistant but typically more expensive per gigabyte than magnetic storage. Optical storage is cheap and portable but has limited capacity and slower access times. The choice depends on the application: e.g., an SSD for a laptop boot drive, or a magnetic HDD for a large backup server.
固态存储速度更快、更抗震，但每 GB 成本通常高于磁存储。光存储廉价便携，但容量有限且访问速度较慢。选择取决于应用场景：例如，笔记本电脑启动盘选用 SSD，大型备份服务器选用磁 HDD。
9. Software & Programming Languages | 软件与编程语言
Software is divided into system software and application software. System software includes the operating system (OS), utilities, and drivers, which manage hardware and provide a platform for applications. Application software performs specific user‑oriented tasks, such as word processing, web browsing, or gaming.
软件分为系统软件和应用软件。系统软件包括操作系统（OS）、实用工具和驱动程序，负责管理硬件并为应用程序提供平台。应用软件执行面向用户的特定任务，如文字处理、网页浏览或游戏。
Programming languages are classified as high‑level (Python, Java) or low‑level (assembly, machine code). High‑level languages are easier for humans to read and write, while low‑level languages give direct control over hardware. Translation is performed by compilers, interpreters, or assemblers. A compiler translates the whole source code into machine code at once, while an interpreter translates and executes line by line.
编程语言分为高级语言（Python、Java）和低级语言（汇编、机器码）。高级语言更易读易写，低级语言则能直接控制硬件。翻译由编译器、解释器或汇编器完成。编译器一次性将整个源代码翻译为机器码，解释器则逐行翻译并执行。
10. Networks & the Internet | 网络与互联网
A network is a collection of devices connected to share resources. LANs (Local Area Networks) cover a small geographical area, while WANs (Wide Area Networks) cover large distances, often using public infrastructure. Common topologies include star, bus, ring, and mesh, each with its own resilience and cost considerations.
网络是连接在一起以共享资源的设备集合。LAN（局域网）覆盖较小地理区域，WAN（广域网）覆盖远距离，通常使用公共基础设施。常见拓扑结构包括星形、总线形、环形和网状，各自具有不同的可靠性和成本考量。
Protocols define rules for communication. TCP/IP is the fundamental suite of the internet; HTTP/HTTPS is used for web pages; FTP for file transfer; SMTP/POP3/IMAP for email. Network hardware includes routers, switches, hubs, and NICs. The roles of IP addresses, MAC addresses, and DNS must be understood.
协议定义了通信规则。TCP/IP 是互联网的基础协议簇；HTTP/HTTPS 用于网页；FTP 用于文件传输；SMTP/POP3/IMAP 用于电子邮件。网络硬件包括路由器、交换机、集线器和网卡。必须理解 IP 地址、MAC 地址和 DNS 的作用。
11. Database Concepts | 数据库概念
A database is a structured collection of data. In a relational database, data is organised into tables with rows (records) and columns (fields). Each table has a primary key that uniquely identifies each record. Tables can be linked using foreign keys, which refer to primary keys in other tables, reducing data redundancy.
数据库是结构化的数据集合。在关系数据库中，数据被组织成包含行（记录）和列（字段）的表。每个表都有一个能够唯一标识每条记录的主键。表可以通过外键关联，外键引用其他表的主键，从而减少数据冗余。
SQL (Structured Query Language) is used to manage data. Common commands include SELECT to retrieve data, INSERT to add records, UPDATE to modify data, and DELETE to remove records. The design of a flat‑file database often leads to duplication, which relational databases solve through normalisation.
SQL（结构化查询语言）用于管理数据。常用命令包括 SELECT 检索数据、INSERT 添加记录、UPDATE 修改数据和 DELETE 删除记录。平面文件数据库的设计常导致数据重复，关系数据库通过规范化解决此问题。
12. Ethical, Legal & Environmental Issues | 道德、法律与环境问题
The use of computers raises important ethical considerations such as privacy, plagiarism, and digital divide. Laws like the Data Protection Act and Computer Misuse Act govern the handling of personal data and cybercrime. Copyright and software licensing also regulate how digital content can be used and distributed.
计算机的使用引发了重要的道德考量，如隐私、剽窃和数字鸿沟。数据保护法和计算机滥用法等法律规范了个人数据的处理和网络犯罪。版权和软件许可也规范了数字内容的使用和分发方式。
Environmental impacts include energy consumption by data centres and the growing problem of e‑waste. Responsible manufacturing, recycling schemes, and energy‑efficient hardware can mitigate some of these effects. Understanding these wider impacts prepares students to become informed digital citizens.
环境影响包括数据中心的能源消耗和日益严重的电子垃圾问题。负责任的制造、回收计划和节能硬件可以缓解部分影响。了解这些更广泛的影响，有助于学生成为有见识的数字公民。
Published by TutorHao | Computer Science Revision Series | aleveler.com
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