📚 Year 9 AQA Computer Science: Core Knowledge Summary | Year 9 AQA 计算机：核心知识点梳理
This guide covers the essential knowledge for Year 9 AQA Computer Science, building a strong foundation in systems, data representation, programming, networks, and digital responsibility. Each section pairs key English explanations with their Chinese translations to support bilingual learning.
本指南涵盖 Year 9 AQA 计算机科学的核心知识，为系统、数据表示、编程、网络和数字责任打下坚实基础。每个部分都提供英文要点和中文对照，帮助双语学习。
1. Introduction to Computer Systems | 计算机系统简介
Process → Output model. It consists of hardware (physical parts) and software (programs).
计算机系统遵循输入 → 处理 → 输出模型，将输入数据处理为有意义的输出。它由硬件（物理部件）和软件（程序）组成。
The CPU (Central Processing Unit) is the ‘brain’ of the computer, responsible for executing instructions. It contains the Control Unit (CU), Arithmetic Logic Unit (ALU), and registers.
CPU（中央处理器）是计算机的“大脑”，负责执行指令。它包含控制单元（CU）、算术逻辑单元（ALU）和寄存器。
Modern CPUs follow the von Neumann architecture, which stores both data and programs in the same memory. This fetch-decode-execute cycle repeats billions of times per second.
现代 CPU 遵循冯·诺依曼架构，将数据和程序存储在同一内存中。取指-译码-执行周期每秒重复数十亿次。
- Input devices: keyboard, mouse, scanner, microphone.
- 输入设备：键盘、鼠标、扫描仪、麦克风。
- Output devices: monitor, printer, speakers.
- 输出设备：显示器、打印机、扬声器。
- Embedded systems are special-purpose computers inside larger devices (e.g., microwave, car engine).
- 嵌入式系统是位于大型设备内部的专用计算机（如微波炉、汽车引擎）。
2. Hardware Components | 硬件组件
The main hardware components inside a desktop computer are the motherboard, CPU, RAM, storage drives, power supply, and cooling system. They connect via buses that carry data, addresses, and control signals.
台式计算机内部的主要硬件组件包括主板、CPU、内存、存储驱动器、电源和冷却系统。它们通过传输数据、地址和控制信号的总线连接。
The CPU performance is affected by three factors: clock speed (measured in GHz), number of cores, and cache size. A higher clock speed means more cycles per second; more cores allow true parallel processing.
CPU 性能受三个因素影响：时钟速度（以 GHz 计量）、核心数量和缓存大小。时钟速度越高，每秒周期数越多；更多核心可实现真正的并行处理。
RAM (Random Access Memory) is volatile main memory that temporarily holds data and programs currently in use. When the power is off, RAM contents are lost.
RAM（随机存取存储器）是易失性主存，临时保存当前使用的数据和程序。断电后，RAM 内容会丢失。
Storage devices such as HDDs (hard disk drives) and SSDs (solid-state drives) provide non-volatile, long-term storage. SSDs are faster and more durable because they have no moving parts.
存储设备如 HDD（硬盘驱动器）和 SSD（固态驱动器）提供非易失性的长期存储。SSD 更快更耐用，因为没有活动部件。
| Component | Function |
|---|---|
| Motherboard | Connects all components; distributes power and signals. |
| GPU | Specialised for rendering images and video. |
| PSU | Converts mains electricity to low DC voltage. |
| 组件 | 功能 |
|---|---|
| 主板 | 连接所有组件；分配电力和信号。 |
| GPU | 专用于渲染图像和视频。 |
| 电源 (PSU) | 将市电转换为低压直流电。 |
3. Memory and Storage | 内存与存储
Memory and storage both hold data, but memory is temporary and directly accessible by the CPU, whereas storage is permanent and slower. The hierarchy includes registers, cache, RAM, and secondary storage.
内存与存储都保存数据，但内存是临时的且 CPU 可直接访问，而存储是永久的且较慢。层级包括寄存器、缓存、RAM 和辅助存储。
ROM (Read Only Memory) is non-volatile and stores the BIOS/boot firmware. It cannot be easily modified. Virtual memory uses part of the hard drive as if it were RAM when physical RAM is full.
ROM（只读存储器）是非易失性的，存储 BIOS/引导固件。它不能轻易修改。当物理内存已满时，虚拟内存将硬盘的一部分当作 RAM 使用。
Secondary storage can be magnetic (HDD), optical (CD, DVD, Blu-ray), or solid state (SSD, USB flash). Each has different capacities, speeds, portability, and cost per GB.
辅助存储可以是磁性的（HDD）、光学的（CD、DVD、蓝光）或固体的（SSD、U 盘）。每种在容量、速度、便携性和每 GB 成本上都有不同。
- Volatile memory: loses data when power is off (e.g., RAM).
- 非易失性存储：断电后保留数据（如 ROM、SSD）。
- Cache: very fast, small memory located close to the CPU to speed up access to frequently used data.
- 缓存：位于 CPU 附近的高速小容量存储器，用于加快对常用数据的访问。
bits) → kilobyte (KB, approx. 1000 bytes) → megabyte (MB) → gigabyte (GB) → terabyte (TB).
数据存储单位：比特 (b) → 字节 (B, 8 位) → 千字节 (KB, 约 1000 字节) → 兆字节 (MB) → 吉字节 (GB) → 太字节 (TB)。
4. Data Representation: Binary and Hexadecimal | 数据表示：二进制与十六进制
Computers use binary (base‑2) because electronic circuits have two stable states – on (1) and off (0). All data, including numbers, text, and images, is represented as binary digits.
计算机使用二进制（基数为 2），因为电路有两种稳定状态——开（1）和关（0）。所有数据，包括数字、文本和图像，都以二进制数字表示。
Decimal (base‑10) numbers can be converted to binary. For example, decimal 13 is 1101 (8+4+0+1). The place values are powers of 2: 128, 64, 32, 16, 8, 4, 2, 1 for 8 bits.
十进制（基数为 10）数字可以转换为二进制。例如，十进制 13 是 1101（8+4+0+1）。位权是 2 的幂：对于 8 位，为 128, 64, 32, 16, 8, 4, 2, 1。
Hexadecimal (base‑ a more compact way to represent binary numbers, as one hex digit equals 4 bits (a nibble).
十六进制（基数为 16）使用数字 0-9 和字母 A-F，其中 A=10, B=11, ..., F=15。它是表示二进制的一种更紧凑的方式，因为一位十六进制数等于 4 位二进制（一个半字节）。
=0, 0+1=1, 1+0=1, 1+1=0 carry 1. A 4-bit addition example: 0101 (5) + 0011 (3) = 1000 (8).
二进制加法遵循简单规则：0+0=0, 0+1=1, 1+0=1, 1+1=0 进位 1。一个 4 位加法示例：0101 (5) + 0011 (3) = 1000 (8)。
- Overflow: when the result of an addition exceeds the maximum value a fixed number of bits can hold.
- 溢出：当加法结果超过固定位数所能表示的最大值时发生。
ts left (e.g., 0010 → 0100); dividing by 2 shifts right. This is used for fast arithmetic.
移位操作：乘以 2 左移（如 0010 → 0100）；除以 2 右移。用于快速算术。
5. Data Representation: Characters, Images, Sound | 数据表示：字符、图像、声音
Characters are represented using standard codes. ASCII uses 7 bits for 128 characters (English letters, digits, symbols). Extended ASCII uses 8 bits for 256 characters. Unicode uses up to 32 bits to represent characters from all major languages, including emojis.
字符使用标准编码表示。ASCII 用 7 位表示 128 个字符（英文字母、数字、符号）。扩展 ASCII 用 8 位表示 256 个字符。Unicode 最多使用 32 位来表示所有主要语言的字符，包括表情符号。
its = 4 colours, 8 bits = 256 colours, 24 bits = true colour (about 16.7 million colours).
图像被分解为像素。颜色深度控制每个像素的位数：1 位 = 2 色（黑白），2 位 = 4 色，8 位 = 256 色，24 位 = 真彩色（约 1670 万色）。
ives more detail but larger file size. Image size in bits = width × height × colour depth.
分辨率是图像中像素的数量（宽×高）。更高的分辨率提供更多细节，但文件大小更大。图像大小（位）= 宽 × 高 × 颜色深度。
Sound is sampled at regular intervals to convert analogue waves into digital data. Sample rate (Hz) is how many times per second a sample is taken. Higher sample rate and bit depth give better quality but larger files.
声音以固定间隔采样，将模拟波转换为数字数据。采样率（Hz）是每秒采样的次数。更高的采样率和位深度提供更好的质量，但文件更大。
ds) × channels. Compression (lossy and lossless) reduces file size but may affect quality.
声音文件大小 = 采样率 × 位深度 × 时长（秒） × 声道数。压缩（有损和无损）减少文件大小，但可能影响质量。
6. Introduction to Algorithms | 算法简介
An algorithm is a step-by-step procedure to solve a problem. It must be unambiguous, have a clear start and end, and produce the correct output for all valid inputs.
算法是解决问题的一步步过程。它必须无歧义，有明确的开始和结束，并且对于所有有效输入都能产生正确的输出。
Algorithms can be expressed using pseudocode (structured English) or flowcharts. Flowcharts use standard symbols: oval for start/end, parallelogram for input/output, rectangle for process, diamond for decision.
算法可以用伪代码（结构化英语）或流程图表达。流程图使用标准符号：椭圆形表示开始/结束，平行四边形表示输入/输出，矩形表示处理过程，菱形表示判断。
Searching algorithms: linear search checks each item one by one; binary search works on sorted lists by repeatedly dividing the search interval in half. Binary search is faster for large datasets.
搜索算法：线性搜索逐个检查每个项目；二分查找适用于已排序列表，通过反复将搜索区间减半来工作。对于大数据集，二分查找更快。
Sorting algorithms: bubble sort repeatedly swaps adjacent out-of-order elements; merge sort splits and merges lists. Merge sort is generally more efficient than bubble sort.
排序算法：冒泡排序反复交换相邻的乱序元素；归并排序分割再合并列表。归并排序通常比冒泡排序更高效。
Algorithm efficiency is measured using Big O notation, describing how runtime or memory grows with input size. For instance, linear search is O(n), binary search is O(log n).
算法效率用大 O 表示法衡量，描述运行时或内存如何随输入规模增长。例如，线性搜索是 O(n)，二分查找是 O(log n)。
7. Programming Basics with Python | Python 编程基础
store data of different types: integer, float, string, boolean. In Python, assignment uses ‘=’, e.g., name = "Alice". Variable names should be meaningful and follow naming conventions.
变量存储不同类型的数据：整型、浮点型、字符串、布尔型。Python 中使用 ‘=’ 赋值，如 name = "Alice"。变量名应有意义并遵循命名约定。
The three basic programming constructs are sequence, selection, and iteration. Sequence is the execution of instructions in order.
三种基本编程结构是顺序、选择和迭代。顺序是按顺序执行指令。
Selection uses if, elif, else to make decisions. Comparison operators: ==, !=, >, <, >=, <=. Logical operators: and, or, not.
选择使用 if、elif、else 进行决策。比较运算符：==, !=, >, <, >=, <=。逻辑运算符：and, or, not。
Iteration: for loops repeat a fixed number of times using range(); while loops repeat as long as a condition is true. Avoid infinite loops.
迭代：for 循环使用 range() 重复固定次数；while 循环只要条件为真就重复。避免无限循环。
- String manipulation: len(), .upper(), .lower(), concatenation (+), slicing.
- 字符串操作：len()、.upper()、.lower()、拼接 (+)、切片。
Lists (arrays) store multiple items. Indexing starts at 0. Useful list methods: append(), remove(), sort(), pop().
列表（数组）存储多个项目。索引从 0 开始。常用列表方法：append()、remove()、sort()、pop()。
Input from user: input() returns a string, often cast to int or float. Output: print(). Comments start with # and explain code.
用户输入：input() 返回字符串，常转换为 int 或 float。输出：print()。注释以 # 开头，解释代码。
8. Computer Networks Basics | 计算机网络基础
A network is two or more computers connected to share resources (files, printers, internet). Benefits include resource sharing, communication, and centralised management.
网络是两台或多台计算机连接起来共享资源（文件、打印机、互联网）。好处包括资源共享、通信和集中管理。
Types of networks: LAN (Local Area Network) covers a small geographic area (school, office); WAN (Wide Area Network) spans large distances, often using leased lines or the internet.
网络类型：LAN（局域网）覆盖小地理区域（学校、办公室）；WAN（广域网）跨越长距离，通常使用租用线路或互联网。
Network topologies: star – all devices connect to a central switch; bus – all on a single cable; mesh – devices connect to many others. Star is common in modern LANs because a failure in one cable doesn't affect the whole network.
网络拓扑：星型——所有设备连接到中央交换机；总线型——全部连接在一根电缆上；网状——设备与许多其他设备连接。星型在现代局域网中很普遍，因为单根电缆故障不会影响整个网络。
Network hardware: switches direct data to specific devices, routers connect different networks (e.g., home to ISP), NIC (Network Interface Card) provides physical connection.
网络硬件：交换机将数据导向特定设备，路由器连接不同网络（如家庭到 ISP），NIC（网络接口卡）提供物理连接。
IP addressing (e.g., 192.168.1.1) uniquely identifies devices. MAC addresses are hardware-based identifiers. DNS translates domain names into IP addresses.
IP 地址（如 192.168.1.1）唯一标识设备。MAC 地址是基于硬件的标识符。DNS 将域名转换为 IP 地址。
Protocols: TCP/IP governs internet communication; HTTP/HTTPS for web pages; FTP for file transfer; SMTP/POP for email. HTTPS encrypts data for security.
协议：TCP/IP 管理互联网通信；HTTP/HTTPS 用于网页；FTP 用于文件传输；SMTP/POP 用于电子邮件。HTTPS 加密数据以保障安全。
9. Cyber Security Essentials | 网络安全要点
Cyber security defends systems from attacks that aim to steal, damage, or disrupt. Threats include malware (viruses, worms, trojans), phishing, social engineering, denial-of-service (DoS), and SQL injection.
网络安全保护系统免受旨在窃取、破坏或干扰的攻击。威胁包括恶意软件（病毒、蠕虫、特洛伊木马）、网络钓鱼、社会工程、拒绝服务攻击（DoS）和 SQL 注入。
Social engineering manipulates people into giving confidential information. Phishing emails trick users into clicking malicious links. Always verify sender identity and avoid unsolicited attachments.
社会工程操纵人们泄露机密信息。网络钓鱼邮件诱骗用户点击恶意链接。始终验证发件人身份并避免意外附件。
Poor cyber security can result in data loss, financial damage, identity theft, and reputational harm. Organisations must follow data protection laws (like GDPR) to safeguard personal data.
网络安全不善会导致数据丢失、经济损失、身份盗用和声誉损害。组织必须遵守数据保护法（如 GDPR）以保护个人数据。
Prevention methods: strong passwords (mix of characters, length), two-factor authentication (2FA), firewalls, anti-malware software, regular updates, and encryption.
预防方法：强密码（字符混合、长度）、双因素身份验证（2FA）、防火墙、反恶意软件、定期更新和加密。
- Encryption scrambles data so that only authorised parties with a key can read it. Caesar cipher is a simple substitution cipher.
- 加密打乱数据，只有拥有密钥的授权方才能读取。凯撒密码是一种简单的替换密码。
Penetration testing and ethical hacking help organisations find vulnerabilities before criminals do.
渗透测试和道德黑客帮助组织在犯罪分子之前发现漏洞。
10. Software: System and Application | 软件：系统与应用
Software is divided into system software and application software. System software includes the operating system (OS), utility programs, and drivers. Application software performs specific tasks for users (e.g., word processor, browser).
软件分为系统软件和应用软件。系统软件包括操作系统（OS）、实用程序和驱动程序。应用软件为用户执行特定任务（如文字处理器、浏览器）。
Functions of the OS: managing hardware (CPU, memory, I/O), providing a user interface (GUI or CLI), multitasking, file management, user account control, and security.
操作系统的功能：管理硬件（CPU、内存、I/O）、提供用户界面（图形界面或命令行）、多任务、文件管理、用户账户控制和安全性。
Utility software: antivirus, disk defragmenter, backup, compression, encryption. These maintain system performance and protect data.
实用软件：防病毒、磁盘碎片整理、备份、压缩、加密。这些维持系统性能并保护数据。
Open source software (e.g., Linux, Python) allows users to access and modify the source code. Proprietary software (e.g., Microsoft Windows) is owned and restricted. Open source often encourages collaboration and customisation.
开源软件（如 Linux、Python）允许用户访问和修改源代码。专有软件（如 Microsoft Windows）归所有者所有并受限制。开源软件通常鼓励协作和定制。
Firmware is low-level software stored in ROM, providing basic control for hardware. Examples: BIOS, embedded system control programs.
固件是存储在 ROM 中的底层软件，为硬件提供基本控制。示例：BIOS、嵌入式系统控制程序。
11. Legal and Ethical Issues | 法律与道德问题
The Computer Misuse Act 1990 makes it illegal to access computer material without permission (hacking), with intent to commit further offences, and to impair computer operation (e.g., malware).
1990 年《计算机滥用法》规定，未经许可访问计算机资料（黑客行为）、意图实施进一步犯罪以及破坏计算机运行（如恶意软件）均为非法。
The Data Protection Act 2018 (incorporating GDPR) requires organisations to keep personal data secure, accurate, and used only for specified purposes. Individuals have rights to access and correct their data.
2018 年《数据保护法》（包含 GDPR）要求组织确保个人数据安全、准确，并仅用于特定目的。个人有权访问和更正自己的数据。
Copyright, Designs and Patents Act protects intellectual property. Software piracy, downloading copyrighted content without permission, and plagiarism are illegal.
《版权、设计和专利法》保护知识产权。软件盗版、未经许可下载受版权保护的内容以及抄袭均属违法。
Ethical issues in computing include privacy concerns (surveillance, data harvesting), digital divide (inequality in access), environmental impact (e-waste, energy consumption), and the responsible use of AI.
计算领域的道德问题包括隐私担忧（监视、数据收集）、数字鸿沟（获取机会不平等）、环境影响（电子垃圾、能源消耗）以及负责任地使用人工智能。
The digital divide is the gap between those who have access to technology and the internet and those who do not. It affects education, employment, and social participation.
数字鸿沟是能够获取技术和互联网的人与无法获取的人之间的差距。它影响教育、就业和社会参与。
All software developers and users should adhere to codes of conduct and consider the broader impact of technology on society.
所有软件开发者和用户都应遵守行为准则，并考虑技术对社会的广泛影响。
12. Summary and Revision Tips | 总结与复习技巧
Year 9 AQA Computer Science covers a wide range of topics that build the foundation for GCSE. Key areas include: computer systems, data representation (binary, hex, images, sound), programming constructs (sequence, selection, iteration), networks, security, software, and legal/ethical understanding.
Year 9 AQA 计算机科学涵盖广泛主题，为 GCSE 奠定基础。关键领域包括：计算机系统、数据表示（二进制、十六进制、图像、声音）、编程结构（顺序、选择、迭代）、网络、安全、软件以及法律/道德理解。
To revise effectively: create flashcards for definitions and key facts, practice binary and hex conversions, write Python code snippets for common tasks, draw and label network diagrams, and test yourself with past exam-style questions.
有效复习：制作抽认卡记忆定义和关键事实，练习二进制和十六进制转换，为常见任务编写 Python 代码片段，绘制并标注网络图，并用历年真题风格的问题自我测试。
- Use pseudocode to describe algorithms before coding.
- 在编程前用伪代码描述算法。
- Explain concepts aloud in both English and Chinese.
- 用英文和中文大声解释概念。
Regular recall and practice with binary arithmetic, data size calculations, and identifying programming errors will strengthen your understanding. Remember that ethical considerations connect all topics.
定期回忆并练习二进制算术、数据大小计算以及识别编程错误，将加深你的理解。记住，道德考量贯穿所有主题。
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