📚 Core Knowledge Revision for Year 11 AQA Computer Science | Year 11 AQA 计算机：核心知识点梳理
This comprehensive guide covers the essential topics for Year 11 AQA Computer Science (8525). From algorithms and programming to data representation, networking and cybersecurity, each section distils the key concepts you must master for the exams. Use it to reinforce your understanding and identify any areas that need extra practice.
本指南梳理了 AQA 计算机科学（8525）Year 11 的核心主题。内容涵盖算法与编程、数据表示、计算机网络以及网络安全等，每一小节都提炼了你必须掌握的考试要点。它可以帮你巩固理解，并发现需要加强练习的地方。
1. Algorithms and Computational Thinking | 算法与计算思维
An algorithm is a step-by-step sequence of instructions that solves a problem. Computational thinking uses abstraction, decomposition and algorithmic thinking to break down complex tasks into manageable parts.
算法是解决问题的逐步指令序列。计算思维利用抽象、分解和算法思维，将复杂任务拆解成可处理的部分。
Searching algorithms include linear search, which checks each element in turn, and binary search, which repeatedly halves a sorted list. Binary search is far more efficient on large datasets because its time complexity is O(log n), while linear search is O(n).
搜索算法包括线性搜索（逐个检查元素）和二分搜索（在有序列表中反复折半）。在大数据集上二分搜索效率高得多，其时间复杂度为 O(log n)，而线性搜索为 O(n)。
Sorting algorithms such as bubble sort compare and swap adjacent items until the list is sorted; insertion sort builds a sorted sub-list by taking items one by one; merge sort uses a divide-and-conquer approach to split, sort and merge. You should be able to trace these algorithms and understand their efficiencies.
排序算法中，冒泡排序比较并交换相邻项直到列表有序；插入排序通过逐个取出元素构建有序子列表；归并排序使用分治法进行拆分、排序与合并。你需要能够追踪这些算法并理解它们的效率。
2. Programming Techniques and Data Structures | 编程技巧与数据结构
Programming relies on variables and constants of different data types: integer, real (float), Boolean, character and string. Variable names should be meaningful and follow a consistent naming convention, while constants store values that never change during execution.
编程依赖不同数据类型的变量和常量：整型、实型（浮点）、布尔型、字符型和字符串。变量名应有意义且遵循一致的命名约定，常量则存储执行期间不变的值。
Sequence, selection (IF-ELSE/SWITCH) and iteration (FOR, WHILE, REPEAT-UNTIL) form the backbone of structured programming. Nesting these constructs correctly is essential, and you must be able to read and write pseudocode that uses them.
顺序、选择（IF-ELSE/SWITCH）和迭代（FOR, WHILE, REPEAT-UNTIL）构成了结构化编程的骨架。正确嵌套这些结构至关重要，你必须能读写使用它们的伪代码。
One-dimensional and two-dimensional arrays store multiple items under a single identifier. String manipulation involves length, substring, concatenation and character retrieval. Subroutines (procedures and functions) promote code reuse. Functions return a value, while procedures do not.
一维和二维数组用单个标识符存储多个数据项。字符串操作涉及长度、子串、连接和字符提取。子程序（过程和函数）促进代码复用。函数返回值，过程不返回值。
3. Data Representation | 数据表示
Computers use binary (0 and 1). Denary to binary conversion uses place values (128,64,32,16,8,4,2,1). Hexadecimal (base-16) is a compact way to represent nibbles, using digits 0-F. For example, the binary 1010 1111 is 0xAF. Denary 200 is 0xC8.
计算机使用二进制（0 和 1）。十进制转二进制使用位值（128,64,32,16,8,4,2,1）。十六进制（基16）用 0-F 紧凑表示半字节，例如二进制 1010 1111 为 0xAF。十进制 200 是 0xC8。
Units of data: 1 nibble = 4 bits, 1 byte = 8 bits, then kilobyte (KB), megabyte (MB), gigabyte (GB) and terabyte (TB). You need to know conversions up to TB and understand that file sizes are often given in powers of 2 or 10.
数据单位：1 半字节 = 4 位，1 字节 = 8 位，然后是千字节（KB）、兆字节（MB）、吉字节（GB）和太字节（TB）。你需要掌握到 TB 的转换，并知道文件大小常以 2 的幂或 10 的幂表示。
Binary addition follows simple rules (0+0=0, 0+1=1, 1+1=0 carry 1). An overflow occurs when the result exceeds the fixed number of bits. Binary shifts multiply (left shift) or divide (right shift) by powers of 2 efficiently.
二进制加法遵循简单规则（0+0=0, 0+1=1, 1+1=0 进位1）。当结果超出固定位数时发生溢出。二进制移位可高效实现乘（左移）或除（右移）2 的幂。
Text: ASCII uses 7 bits, extended ASCII 8; Unicode (e.g. UTF-8) covers worldwide characters. Images: composed of pixels; colour depth (bits per pixel) and resolution determine quality and file size. Sound: captured by sampling rate (Hz) and bit depth; higher values give better fidelity but larger files. Compression: lossless (e.g. run-length encoding) retains all data; lossy (e.g. JPEG) removes some data permanently.
文本：ASCII 用 7 位，扩展 ASCII 用 8 位；Unicode（如 UTF-8）覆盖全球字符。图像：由像素构成；色深（每像素位数）和分辨率决定质量和文件大小。声音：通过采样率（Hz）和位深度采集；值越高保真度越好但文件更大。压缩：无损（如游程编码）保留所有数据；有损（如 JPEG）永久移除部分数据。
4. Computer Systems: Hardware and Software | 计算机系统：硬件与软件
The Von Neumann architecture stores both data and instructions in the same memory. Key CPU components: Control Unit (CU) decodes instructions and directs operations; Arithmetic Logic Unit (ALU) performs calculations and logical operations; registers (PC, MAR, MDR, ACC) hold temporary data.
冯·诺依曼体系结构将数据和指令存储在同一内存中。CPU 主要部件：控制单元（CU）解码指令并指挥操作；算术逻辑单元（ALU）执行计算和逻辑运算；寄存器（PC, MAR, MDR, ACC）保存临时数据。
The fetch-decode-execute cycle repeats: fetch the instruction from memory (MAR←PC, MDR←memory), decode it in the CU, then execute (ALU and registers). Factors affecting CPU performance: clock speed (cycles per second), number of cores (parallelism) and cache size (fast, small memory).
取指-解码-执行周期不断重复：从内存取指（MAR←PC, MDR←内存），在 CU 解码，然后执行（ALU 及寄存器）。影响 CPU 性能的因素：时钟速度（每秒周期数）、核心数（并行能力）和缓存大小（快速小容量内存）。
Primary memory: RAM (volatile, stores currently running programs/data) and ROM (non-volatile, stores boot code). Secondary storage: magnetic (HDD – high capacity, mechanical), solid state (SSD – fast, durable, no moving parts) and optical (CD/DVD – portable). Cloud storage provides remote access via the internet.
主存：RAM（易失性，存储正在运行的程序/数据）和 ROM（非易失性，存储引导代码）。辅助存储：磁（HDD – 大容量、机械式）、固态（SSD – 快速、耐用、无移动部件）和光学（CD/DVD – 便携）。云存储通过互联网提供远程访问。
Embedded systems are dedicated computers inside devices (e.g. washing machines, cars). They have limited resources but offer reliability and low power. Operating system software manages hardware, provides a user interface, memory management, multitasking, peripheral management and security.
嵌入式系统是设备内部的专用计算机（如洗衣机、汽车）。它们资源有限但可靠且功耗低。操作系统软件管理硬件，提供用户界面、内存管理、多任务处理、外设管理和安全。
5. Boolean Logic and Logic Gates | 布尔逻辑与逻辑门
Boolean variables can be TRUE or FALSE, represented by 1 and 0. Basic gates: AND (output 1 if both inputs are 1), OR (output 1 if at least one input is 1), NOT (inverts input). NAND and NOR are inverses of AND and OR; XOR outputs 1 when inputs differ.
布尔变量可为 TRUE 或 FALSE，用 1 和 0 表示。基本门：AND（输入均为 1 时输出 1）、OR（至少一个输入为 1 输出 1）、NOT（将输入反向）。NAND 和 NOR 是 AND 与 OR 的反相；XOR 在输入不同时输出 1。
Truth tables map every input combination to the output. For example, AND: A=0,B=0 → 0; 0,1 → 0; 1,0 → 0; 1,1 → 1. You must be able to draw and interpret logic circuits using the standard gate symbols, and write Boolean expressions like Q = (A ∧ B) ∨ ¬C.
真值表将每种输入组合映射到输出。例如 AND：A=0,B=0 → 0; 0,1 → 0; 1,0 → 0; 1,1 → 1。你必须能绘制并解读使用标准门符号的逻辑电路，并写出如 Q = (A ∧ B) ∨ ¬C 的布尔表达式。
6. Computer Networks and Topologies | 计算机网络与拓扑结构
A LAN covers a small geographical area (e.g. school); a WAN spans large distances (e.g. the internet). PANs connect personal devices. Networks can be wired (Ethernet, reliable high speed) or wireless (Wi‑Fi, Bluetooth, greater mobility but potential interference).
LAN 覆盖小地理区域（如学校）；WAN 跨越长距离（如互联网）。PAN 连接个人设备。网络可以是有线（以太网，可靠高速）或无线（Wi‑Fi、蓝牙，移动性好但可能有干扰）。
Topologies: star (all devices connect to a central switch; easy to manage, single point of failure), bus (single backbone cable; cheap, difficult to troubleshoot), ring (data travels in one direction; no collisions but one break halts network), mesh (full or partial; robust and redundant but costly).
拓扑结构：星形（所有设备连接中央交换机；易于管理，单点故障），总线形（单一主干电缆；便宜，故障难排除），环形（数据单向传输；无冲突，但一处断开全网瘫痪），网状（全连接或部分连接；健壮、冗余但昂贵）。
IP addresses (IPv4 like 192.168.1.10) identify devices on a network; MAC addresses are hard-coded identifiers for network interfaces. In client-server networks, the server provides resources; in peer-to-peer, all devices share equally. Each has trade-offs in security, cost and management.
IP 地址（如 IPv4 192.168.1.10）标识网络上的设备；MAC 地址是网络接口的固定标识符。在客户端-服务器网络中，服务器提供资源；在点对点网络中，所有设备平等共享。两者在安全性、成本和管理上各有取舍。
7. Network Protocols and the Four-Layer Model | 网络协议与四层模型
The TCP/IP stack has four layers: Application, Transport, Internet and Network Access. Each layer uses specific protocols to ensure data is communicated reliably from sender to receiver.
TCP/IP 协议栈分为四层：应用层、传输层、互联网层和网络接入层。每层使用特定协议确保数据可靠地从发送方传送到接收方。
Application layer protocols: HTTP (web pages), HTTPS (secure web), FTP (file transfer), SMTP (sending email), IMAP and POP3 (receiving email). SSH provides secure remote access. The Transport layer uses TCP for reliable, ordered delivery with error checking, or UDP for faster, connectionless streaming.
应用层协议：HTTP（网页）、HTTPS（安全网页）、FTP（文件传输）、SMTP（发送邮件）、IMAP 和 POP3（接收邮件）。SSH 提供安全远程访问。传输层使用 TCP 实现可靠、有序的差错校验传输，或 UDP 实现更快、无连接的流传输。
Data is split into packets. Each packet contains source and destination IP addresses, sequence number and payload. Packet switching allows packets to travel different routes and be reassembled at the destination. This makes the network efficient and fault-tolerant.
数据被拆分成数据包。每个数据包包含源和目标的 IP 地址、序号和有效载荷。分组交换允许数据包经不同路径传输并在目的地重组，使网络高效且具有容错性。
8. Cyber Security Threats and Prevention | 网络安全威胁与防护
Threats include: malware (viruses, worms, trojans, ransomware), phishing (deceptive emails to steal credentials), brute-force attacks (repeated password guessing), Denial of Service (DoS – flooding servers), SQL injection (inserting malicious SQL into web forms), and social engineering (manipulating people).
威胁包括：恶意软件（病毒、蠕虫、木马、勒索软件）、网络钓鱼（欺骗性邮件盗取凭证）、暴力攻击（反复猜测密码）、拒绝服务（DoS – 淹没服务器）、SQL 注入（在 Web 表单中插入恶意 SQL）以及社会工程学（操纵人的心理）。
Prevention methods: regular penetration testing identifies vulnerabilities; anti-malware software detects and removes threats; firewalls filter incoming and outgoing traffic; user access levels restrict permissions; encryption scrambles data; physical security (locks, biometrics) protects hardware. Strong password policies and staff training are essential.
防护方法：定期渗透测试发现漏洞；反恶意软件检测并移除威胁；防火墙过滤进出流量；用户访问级别限制权限；加密打乱数据；物理安全（门锁、生物识别）保护硬件。强密码策略和员工培训同样关键。
9. Relational Databases and SQL | 关系型数据库与 SQL
A relational database stores data in tables (relations). Each table consists of fields (columns) and records (rows). A primary key uniquely identifies each record. A foreign key links tables by referencing a primary key in another table, maintaining referential integrity.
关系型数据库将数据存储在表（关系）中。每个表包含字段（列）和记录（行）。主键唯一标识每条记录。外键通过引用另一表的主键来关联各表，从而维护参照完整性。
SQL commands you must know: SELECT field1, field2 FROM table WHERE condition ORDER BY field ASC|DESC; INSERT INTO table (fields) VALUES (values); UPDATE table SET field=value WHERE condition; DELETE FROM table WHERE condition. Wildcards like * select all fields; % and _ are used with LIKE.
你必须掌握的 SQL 命令：SELECT 字段1, 字段2 FROM 表 WHERE 条件 ORDER BY 字段 ASC|DESC；INSERT INTO 表 (字段) VALUES (值)；UPDATE 表 SET 字段=值 WHERE 条件；DELETE FROM 表 WHERE 条件。通配符 * 选择全部字段；% 和 _ 配合 LIKE 使用。
Validation checks (presence, length, range, format) help ensure only sensible data enters the database. Normalisation reduces data redundancy by splitting tables properly.
验证检查（存在、长度、范围、格式）有助于确保只有合理数据进入数据库。规范化通过适当拆分表来减少数据冗余。
10. Ethical, Legal and Environmental Impacts | 伦理、法律与环境影响
Legislation: The Data Protection Act 2018 (UK GDPR) governs personal data handling—data must be used fairly, kept secure and not retained longer than necessary. The Computer Misuse Act 1990 criminalises unauthorised access, modification and the creation of malware. The Copyright, Designs and Patents Act 1988 protects original work from unauthorised copying.
立法：《2018 数据保护法》（英国 GDPR）规范个人数据处理——数据必须公平使用、安全保存且不得超过必要期限保留。《1990 计算机滥用法》将未经授权访问、修改及制造恶意软件定为犯罪。《1988 版权、外观设计与专利法》保护原创作品免遭未经允许的复制。
Open source software allows users to view and modify the source code (e.g. Linux), often free and community-driven. Proprietary software hides the source code; users pay for a license (e.g. Microsoft Windows). Both have impacts on cost, support and security.
开源软件允许用户查看和修改源代码（如 Linux），通常免费并由社区驱动。专有软件隐藏源代码；用户付费获取授权（如 Microsoft Windows）。二者在成本、支持与安全性上各有影响。
Social and environmental concerns: The digital divide leaves some people without access to technology. Over-reliance on automation can reduce employment. Environmental issues include energy consumption of data centres, electronic waste (e-waste) and rare-earth mineral extraction. Responsible computing includes recycling hardware and designing energy-efficient algorithms.
社会与环境问题：数字鸿沟使部分人无法接触技术。对自动化的过度依赖可能减少就业。环境问题包括数据中心能耗、电子废物（e-waste）和稀土开采。负责任的计算包含硬件回收和设计节能算法。
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