📚 Year 11 Cambridge Computer Science: Core Concepts Summary | 核心知识点梳理
This comprehensive revision guide outlines the key topics covered in Year 11 Cambridge Computer Science. It is designed to help students consolidate their understanding and prepare confidently for examinations. Each section pairs essential theory with clear bilingual explanations, covering data representation, hardware, software, networking, cybersecurity, algorithms, programming, databases, and logic.
本综合复习指南梳理了 Year 11 剑桥计算机科学的核心知识点，旨在帮助学生巩固理解、自信备考。每个章节都采用中英双语清晰讲解关键理论，内容涵盖数据表示、硬件、软件、网络、网络安全、算法、编程、数据库和逻辑等领域。
1. Data Representation | 数据表示
Computers process and store data in binary form, using only the digits 0 and 1. All types of information – numbers, text, images, and sound – must be converted into binary for the computer to understand.
计算机以二进制形式处理和存储数据，仅使用数字0和1。所有类型的信息——数字、文本、图像和声音——都必须转换为二进制才能被计算机理解。
Denary (base-10) numbers are converted to binary by successive division by 2. To convert binary to denary, multiply each bit by its place value (power of 2) and sum the results.
十进制数转换为二进制采用连续除以2取余数的方法。二进制转换为十进制则是将每一位乘以其位值（2的幂）再求和。
Hexadecimal (base-16) uses digits 0-9 and letters A-F. It provides a compact way to represent binary values, since each hex digit corresponds to 4 bits (a nibble). Common uses include colour codes and memory addresses.
十六进制使用0-9和A-F，是一种紧凑表示二进制值的方式，每个十六进制位对应4个二进制位（半字节）。常用于颜色代码和内存地址。
Binary addition follows the same rules as denary addition, carrying over when the sum is 2 or more. Overflow occurs when the result exceeds the bit-width, potentially causing errors.
二进制加法遵循与十进制类似的规则，和大于或等于2时产生进位。当结果超出规定的位宽时发生溢出，可能引发错误。
A binary shift moves all bits left or right. Shifting left by one place multiplies the number by 2, while shifting right divides by 2 (integer division), with rightmost bits discarded.
二进制移位将所有位向左或向右移动。左移一位相当于乘以2，右移一位相当于除以2（整除），右侧丢弃的位会丢失。
Negative numbers are stored using two’s complement. The most significant bit (MSB) indicates the sign (1 for negative). To find the two’s complement, invert all bits and add 1.
负数使用二进制补码存储。最高位表示符号（1为负）。求一个数的补码需将所有位取反再加1。
Text characters are encoded using standard sets. ASCII uses 7 or 8 bits, representing 128 or 256 characters. Unicode extends this with multiple encoding forms (e.g. UTF-8) to cover global scripts and emoji.
文本字符通过标准编码集表示。ASCII使用7或8位，表示128或256个字符。Unicode通过多种编码形式（如UTF-8）扩展，涵盖全球文字和表情符号。
Images are stored as bitmaps, a grid of pixels. Each pixel has a colour represented by a binary value; colour depth indicates bits per pixel. More pixels (higher resolution) and deeper colour produce better quality but larger file sizes.
图像以位图形式存储，即像素网格。每个像素的颜色由二进制值表示；颜色深度指每个像素的位数。像素越多（分辨率越高）、颜色越深，质量越好，但文件也越大。
ne audio quality and file size. File size = sample rate × bit depth × duration × channels.
声音通过定期对模拟信号采样实现数字化。采样率和采样精度决定了音频质量和文件大小。文件大小 = 采样率 × 位深度 × 时长 × 声道数。
bits, 1 byte = 8 bits, 1 KB = 1024 bytes, 1 MB = 1024 KB, 1 GB = 1024 MB, 1 TB = 1024 GB.
存储单位按2的幂递进：1个半字节 = 4位，1字节 = 8位，1 KB = 1024字节，1 MB = 1024 KB，1 GB = 1024 MB，1 TB = 1024 GB。
2. Data Transmission | 数据传输
Data can be transmitted in serial (one bit at a time, useful for long distances) or in parallel (multiple bits simultaneously over separate wires, faster but prone to skew over longer cables).
数据可以串行传输（一次一位，适合长距离）或并行传输（多根线同时传输多位，速度快但长距离易出现时序偏差）。
Transmission modes describe direction: simplex is one-way only (e.g. TV broadcast); half-duplex allows two-way but not simultaneously (e.g. walkie-talkie); full-duplex enables simultaneous two-way communication (e.g. phone call).
传输模式描述方向：单工只能单向（如电视广播）；半双工可双向但不可同时（如对讲机）；全双工可同时双向通信（如电话）。
USB (Universal Serial Bus) is a standard interface for connecting peripherals. It supports hot-swapping, provides power, and can daisy-chain many devices; modern versions offer very high transfer speeds.
USB（通用串行总线）是连接外设的标准接口，支持热插拔、供电，并能串联多个设备；现代版本提供极高的传输速度。
Error detection ensures data integrity. Parity check adds an extra bit so the number of 1s is even or odd. Checksum involves summing data bytes and transmitting the sum. Echo check sends data back for verification.
错误检测确保数据完整性。奇偶校验增加一个额外位使1的个数为奇或偶。校验和将数据字节求和并传输该和值。回波检查将数据回传以验证。
ARQ (Automatic Repeat reQuest) uses acknowledgements and timeouts. If no acknowledgement is received within a time window, the data is resent. This combines with checksums to achieve reliable transmission.
自动重复请求使用确认和超时机制。在规定时间内未收到确认则重发数据，再配合校验和即可实现可靠传输。
Packet switching breaks data into packets that travel independently across a network, possibly taking different routes. Each packet carries source and destination addresses and sequence number for reassembly.
分组交换将数据分割为分组，这些分组在网络中独立传输，可能走不同路径。每个分组携带源地址、目标地址和序号，以便重组。
3. Hardware | 硬件
The Central Processing Unit (CPU) is the brain of the computer. It consists of the Control Unit (CU), which directs operations; the Arithmetic Logic Unit (ALU), which performs calculations and logic; and registers, which are small, fast storage locations.
中央处理器(CPU)是计算机的大脑，由控制单元(指导操作)、算术逻辑单元(执行运算和逻辑)以及寄存器(小型高速存储位置)组成。
The von Neumann architecture stores both data and instructions in the same memory, with a single bus system. The fetch-decode-execute cycle fetches an instruction from memory, decodes it, and executes it, repeating continuously.
冯·诺依曼架构将数据和指令存储在同一内存中并使用单一总线系统。取指-译码-执行循环不断从内存取出指令、译码和执行。
Factors affecting CPU performance include clock speed (cycles per second), number of cores (parallel processing), and cache size (high-speed memory close to the CPU that stores frequently used data).
影响CPU性能的因素包括时钟频率(每秒周期数)、内核数量(并行处理)和缓存大小(靠近CPU的高速内存，存储频繁使用的数据)。
Embedded systems are dedicated computers within larger devices (e.g. washing machines, cars). They typically run on microcontrollers and are optimised for a specific task, often with real-time constraints and low power consumption.
嵌入式系统是大型设备内的专用计算机(如洗衣机、汽车)。它们通常由微控制器运行，针对特定任务优化，往往具有实时约束和低功耗要求。
Main memory includes RAM (Random Access Memory), which is volatile and holds data and programs currently in use, and ROM (Read Only Memory), which is non-volatile and stores firmware like the BIOS boot program.
主存储器包括RAM(随机存取存储器，易失性，存放当前使用的数据和程序)和ROM(只读存储器，非易失，存储固件如BIOS引导程序)。
Secondary storage is non-volatile: HDDs use magnetic platters and moving heads, offering large capacity at lower cost; SSDs use flash memory for much higher speed and durability; optical discs (CD, DVD, Blu-ray) and USB flash drives are portable options.
辅助存储器是非易失性的：HDD使用磁盘和移动磁头，成本低容量大；SSD使用闪存，速度更快、更耐用；光盘(CD、DVD、蓝光)和U盘则便于携带。
Input devices (keyboard, mouse, microphone, sensor) send data to the computer. Output devices (monitor, printer, speaker, actuator) present information to the user.
输入设备(键盘、鼠标、麦克风、传感器)向计算机发送数据。输出设备(显示器、打印机、扬声器、执行器)将信息呈现给用户。
4. Software | 软件
System software runs and manages the computer hardware. Application software helps users perform specific tasks, such as word processing, web browsing, or gaming.
系统软件运行和管理计算机硬件。应用软件帮助用户执行特定任务，如文字处理、网页浏览或游戏。
The operating system (OS) provides a user interface, manages memory and processes, handles input/output operations, manages files, and enforces security (e.g. user accounts).
操作系统提供用户界面，管理内存和进程，处理输入/输出操作，管理文件，并实施安全策略(如用户账户)。
Utility software performs maintenance tasks: disk defragmentation reorganises scattered files for faster access; backup software copies data to prevent loss; antivirus software scans for and removes malware; file compression reduces file size.
实用工具软件执行维护任务：磁盘碎片整理重新组织分散文件以加快访问；备份软件复制数据以防丢失；防病毒软件扫描并移除恶意软件；文件压缩减小文件体积。
High-level languages (like Python, Java) resemble human language and are easier to read, but need to be translated into machine code. Low-level languages (assembly language) use mnemonics closer to machine instructions, offering fine control.
高级语言(如Python、Java)接近人类语言、易读易懂，但需要转换为机器码。低级语言(汇编语言)使用助记符，更靠近机器指令，可进行精细控制。
Translators convert source code: a compiler produces an executable file from the entire program before execution; an interpreter translates and executes line by line, which is useful for debugging but generally slower.
翻译器转换源代码：编译器在执行前将整个程序生成可执行文件；解释器逐行翻译和执行，利于调试但通常较慢。
5. The Internet and Its Uses | 互联网及其应用
The Internet is a global network of networks connecting billions of devices. Data is transmitted using protocols – agreed sets of rules. The TCP/IP protocol suite governs how data is packetised, addressed, routed, and received.
互联网是一个由网络组成的全球性网络，连接数十亿设备。数据通过协议(一致同意的规则集)传输。TCP/IP协议族规定了数据打包、寻址、路由和接收的方式。
Every device has a MAC address (Media Access Control), a unique 48-bit hardware identifier assigned to the network interface card. IP addresses (IPv4 or IPv6) are logical and can change, used for routing across networks.
每台设备具有MAC地址(媒体访问控制)，即分配给网卡的唯一48位硬件标识符。IP地址(IPv4或IPv6)是逻辑地址，可以改变，用于跨网络路由。
DNS (Domain Name System) translates human-friendly domain names (e.g. www.example.com) into IP addresses. This process involves a hierarchy of servers: local, root, TLD, and authoritative.
DNS将便于记忆的域名(如www.example.com)转换为IP地址。这一过程涉及一系列服务器：本地DNS、根服务器、顶级域服务器和权威服务器。
Web browsing uses HTTP (Hypertext Transfer Protocol) or its secure version HTTPS, which encrypts data via SSL/TLS. A client sends a request to a web server, which returns the requested resource.
网页浏览使用HTTP，或安全的HTTPS(通过SSL/TLS加密数据)。客户端向Web服务器发送请求，服务器返回所请求的资源。
Cookies are small text files stored on the user’s computer by websites. They remember login details and preferences but raise privacy concerns. Digital signatures and certificates are used to verify identity and data integrity on the internet.
Cookie是网站存储在用户计算机上的小型文本文件，可记住登录信息和偏好，但也引发隐私问题。数字签名和证书用于在互联网上验证身份和数据完整性。
Cryptocurrencies like Bitcoin use blockchain technology – a decentralised, distributed ledger that records transactions securely using cryptographic hashes and proof-of-work mechanisms.
加密货币(如比特币)使用区块链技术——一种去中心化的分布式账本，通过密码哈希和工作量证明机制安全记录交易。
6. Cybersecurity | 网络安全
Malware (malicious software) includes viruses (attaches to programs, spreads), worms (self-replicating), trojans (disguised as legitimate software), spyware (secretly gathers data), and ransomware (encrypts files and demands payment).
恶意软件包括病毒(附着于程序、传播)、蠕虫(自我复制)、特洛伊木马(伪装成合法软件)、间谍软件(秘密收集数据)和勒索软件(加密文件并勒索赎金)。
Social engineering tricks individuals into revealing confidential information. Phishing uses deceptive emails or websites; baiting offers something enticing; pretexting invents scenarios to manipulate victims.
社会工程学诱骗个人泄露机密信息。网络钓鱼使用欺骗性邮件或网站；诱饵攻击提供诱人条件；借口攻击虚构情景操纵受害者。
Brute-force attacks try all possible passwords until the correct one is found. DoS (Denial of Service) attacks overload a server with traffic, making it unavailable. SQL injection inserts malicious SQL code into a database query to manipulate or extract data.
暴力攻击尝试所有可能的密码直到找到正确者。DoS攻击用流量过载服务器致其不可用。SQL注入将恶意SQL代码插入数据库查询以操纵或窃取数据。
Protection methods include firewalls (filter incoming and outgoing traffic based on rules), encryption (scrambles data so only authorised parties can read it), strong passwords (length, complexity, two-factor authentication), and biometrics (fingerprints, face recognition).
防护方法包括防火墙(按规则过滤进出流量)、加密(加扰数据，仅授权方可读取)、强密码(长度、复杂度、双因素认证)和生物识别(指纹、面部识别)。
Regular software updates patch known vulnerabilities. Penetration testing identifies weaknesses so they can be fixed before attackers exploit them. Acceptable use policies educate users about safe behaviour.
定期软件更新修补已知漏洞。渗透测试找出弱点以便在攻击者利用之前修复。可接受使用策略教育用户安全行为。
7. Automated and Emerging Technologies | 自动化与新兴技术
Automation replaces human input with programmed control. Robotics combines sensors, processors, and actuators to perform physical tasks, often in manufacturing, surgery, and exploration.
自动化用编程控制取代人工输入。机器人技术结合传感器、处理器和执行器执行物理任务，常用于制造、手术和探索领域。
Artificial Intelligence (AI) simulates human intelligence, enabling machines to learn, reason, and self-correct. Machine learning, a subset of AI, uses algorithms to identify patterns in data without explicit programming.
人工智能(AI)模拟人类智能，使机器能够学习、推理和自我纠错。机器学习是AI的子集，利用算法从数据中识别模式而无需显式编程。
The Internet of Things (IoT) connects everyday objects (appliances, vehicles, sensors) to the internet, allowing them to collect and exchange data. Applications include smart homes, health monitors, and industrial control.
物联网(IoT)将日常物品(电器、车辆、传感器)连接到互联网，使其能够收集和交换数据。应用包括智能家居、健康监测和工业控制。
Other emerging technologies include autonomous vehicles (self-driving cars using sensors and AI), quantum computing (using qubits for parallel computation), and augmented/virtual reality (AR/VR) for immersive experiences.
其他新兴技术包括自动驾驶汽车(使用传感器和AI的无人驾驶汽车)、量子计算(利用量子比特进行并行计算)以及增强现实/虚拟现实(AR/VR)提供沉浸式体验。
Ethical considerations arise around job displacement, privacy, safety of autonomous systems, and bias in AI algorithms. Governments and organisations are creating guidelines for responsible development.
伦理问题涉及就业取代、隐私、自主系统安全性以及AI算法偏见。政府和组织正制定负责任开发的指导原则。
8. Algorithms and Problem-Solving | 算法与问题解决
An algorithm is a step-by-step procedure to solve a problem. Abstraction removes unnecessary detail to focus on the essential aspects. Decomposition breaks a complex problem into smaller, manageable sub-problems.
算法是解决问题的分步骤过程。抽象去除不必要的细节，聚焦于本质。分解将复杂问题拆分成更小、可管理的子问题。
Flowcharts use standard symbols: ovals for start/end, rectangles for processes, diamonds for decisions, parallelograms for input/output. Arrows show the direction of flow.
流程图使用标准符号：椭圆表示开始/结束，矩形表示处理，菱形表示判断，平行四边形表示输入/输出。箭头指示流程方向。
Pseudocode is a textual method combining programming logic with plain English, avoiding strict syntax. It uses keywords like IF, THEN, ELSE, WHILE, FOR, REPEAT...UNTIL, and INPUT/OUTPUT.
伪代码是一种结合编程逻辑和自然语言的文本描述方法，避免严格语法。它使用 IF、THEN、ELSE、WHILE、FOR、REPEAT...UNTIL 和 INPUT/OUTPUT 等关键词。
Three basic control structures: sequence (executing steps in order), selection (IF-ELSE, CASE), and iteration (loops). These can be combined to create any algorithm.
三种基本控制结构：顺序(按顺序执行步骤)、选择(IF-ELSE、CASE)和迭代(循环)。组合使用可实现任何算法。
Linear search checks each element in a list sequentially until the target is found or the list ends. It does not require the data to be sorted, but is inefficient for large lists (O(n)).
线性查找顺序检查列表中的每个
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