📚 Year 9 OCR Computer Science: Core Knowledge Points Review | Year 9 OCR 计算机：核心知识点梳理
Welcome to your essential Year 9 OCR Computer Science revision guide. This article breaks down the key concepts you will encounter, from hardware and software to programming fundamentals and ethical considerations. Each section presents the core ideas in English followed by Chinese, helping you reinforce your understanding while building bilingual confidence.
欢迎阅读 Year 9 OCR 计算机科学核心复习指南。本文梳理了你将接触到的关键概念，从硬件与软件到编程基础与道德考量。每个部分先以英语呈现核心观点，再以中文进行翻译，帮助你在巩固知识的同时建立双语自信。
1. Introduction to Computer Systems | 计算机系统概论
A computer system is more than just the physical machine you can touch. It combines hardware (the tangible components like the processor, memory and keyboard) with software (the programs and operating system that instruct the hardware). Together they follow the input-process-output model: data enters the system, is manipulated, and meaningful information is produced.
计算机系统不仅仅是你所能触摸的物理机器。它将硬件（处理器、内存、键盘等有形组件）与软件（指挥硬件的程序和操作系统）结合在一起。它们共同遵循输入-处理-输出模型：数据进入系统，经过处理，产生有意义的信息。
Input devices such as a mouse, microphone or sensor feed raw data into the computer. The central processing unit (CPU) then processes this data according to instructions stored in memory. Finally, output devices like a monitor, printer or speaker present the results to the user.
鼠标、麦克风或传感器等输入设备将原始数据送入计算机。中央处理器（CPU）随后根据存储在内存中的指令处理这些数据。最后，显示器、打印机或扬声器等输出设备将结果呈现给用户。
Storage devices are essential for keeping data and software permanently. Primary storage (RAM and ROM) holds data temporarily or permanently for immediate access, while secondary storage (hard drives, SSDs, USB sticks) provides long-term, non-volatile space.
存储设备对于永久保存数据和软件至关重要。主存储器（RAM 和 ROM）临时或永久地保存数据以供即时访问，而辅助存储器（硬盘、固态硬盘、U盘）提供长期的非易失性空间。
2. The CPU and Von Neumann Architecture | CPU 与冯·诺依曼架构
The CPU is often called the 'brain' of the computer. Its speed is measured in gigahertz (GHz), indicating billions of cycles per second. Modern CPUs contain multiple cores, allowing them to process several instructions simultaneously and improving multitasking performance.
CPU 常被称为计算机的“大脑”。其速度以千兆赫兹（GHz）为单位，表示每秒数十亿个周期。现代 CPU 包含多个核心，使其能够同时处理多条指令并提高多任务处理性能。
According to the Von Neumann architecture, a computer stores both program instructions and data in the same memory unit. The CPU repeatedly performs the fetch-decode-execute cycle: it fetches an instruction from memory, decodes what operation is required, and then executes it using the arithmetic logic unit (ALU) and control unit (CU).
根据冯·诺依曼架构，计算机将程序指令和数据存储在同一个内存单元中。CPU 反复执行取指-译码-执行周期：从内存中取出一条指令，译码出需要执行的操作，然后通过算术逻辑单元（ALU）和控制单元（CU）执行该指令。
Key registers inside the CPU, such as the program counter (PC), memory address register (MAR) and accumulator (ACC), hold tiny amounts of data during processing. The cache is a small but very fast memory located close to the CPU, storing frequently used instructions to speed up performance.
CPU 内部的关键寄存器，例如程序计数器（PC）、内存地址寄存器（MAR）和累加器（ACC），在处理过程中暂存少量数据。缓存是一种位于 CPU 附近的小容量但极快的内存，用于存储常用指令以提升性能。
3. Memory and Storage | 内存与存储
Random Access Memory (RAM) is volatile – it loses its contents when the power is turned off. It holds the operating system, applications and data currently in use, allowing the CPU to access them quickly. Read-Only Memory (ROM) is non-volatile and typically stores the boot program (BIOS) that starts the computer.
随机存取存储器（RAM）是易失性的——断电后其内容会丢失。它保存当前正在使用的操作系统、应用程序和数据，使 CPU 能快速访问它们。只读存储器（ROM）是非易失性的，通常存储启动计算机的引导程序（BIOS）。
Secondary storage is needed for long-term retention. Magnetic hard disk drives (HDDs) use spinning platters and are cheap for large capacities. Solid-state drives (SSDs) use flash memory with no moving parts, offering faster access and greater durability. Optical discs (CDs, DVDs) and cloud-based storage provide alternatives for backups and sharing.
辅助存储器用于长期保存数据。磁性硬盘驱动器（HDD）使用旋转盘片，适合大容量且成本较低。固态硬盘（SSD）使用闪存，无活动部件，提供更快的访问速度和更强的耐用性。光盘（CD、DVD）和基于云的存储为备份和共享提供了其他选择。
yte (TB) ≈ 1000 GB. Data transfer speed is often rated in megabytes per second (MB/s) or megabits per second (Mbps).
容量以字节为单位，常用换算为：1 千字节（KB）≈ 1000 字节，1 兆字节（MB）≈ 1000 KB，1 吉字节（GB）≈ 1000 MB，1 太字节（TB）≈ 1000 GB。数据传输速度通常以兆字节每秒（MB/s）或兆比特每秒（Mbps）来评定。
4. Data Representation – Binary & Hexadecimal | 数据表示——二进制与十六进制
Computers use binary because they are built from switches that can only be on (1) or off (0). A single binary digit is called a bit, and a group of 8 bits makes a byte. With n bits you can represent 2ⁿ different values. A nibble is half a byte (4 bits) and is particularly useful when working with hexadecimal.
计算机使用二进制，因为它们由仅能处于开（1）或关（0）状态的开关构成。单个二进制位称为比特，8 个比特组成一个字节。使用 n 个比特可以表示 2ⁿ 个不同的值。一个半字节（4 个比特）在处理十六进制时尤其方便。
+ 4 + 0 + 1 = 13₁₀. Binary addition follows simple rules: 0+0=0, 1+0=1, 1+1=10₂ (carry 1).
将二进制转换为十进制时，每个位的位置权重为 2 的幂。例如，二进制数 1101₂ 为 (1 x 2³) + (1 x 2²) + (0 x 2¹) + (1 x 2⁰) = 8 + 4 + 0 + 1 = 13₁₀。二进制加法遵循简单规则：0+0=0，1+0=1，1+1=10₂（进位 1）。
Hexadecimal (base 16) uses digits 0–9 and letters A–F to represent values 10–15. It is a compact way to express long binary strings: each hex digit represents exactly one nibble. For example, the byte 1010 1111₂ becomes AF₁₆. Hexadecimal is widely used for colour codes and memory addresses.
十六进制（基数为 16）使用数字 0–9 和字母 A–F 表示值 10–15。它是一种紧凑表达长二进制串的方式：每个十六进制数字恰好代表一个半字节。例如，字节 1010 1111₂ 变为 AF₁₆。十六进制广泛用于颜色代码和内存地址。
5. Representing Text, Images and Sound | 文本、图像和声音的表示
Text is stored by assigning a unique binary code to each character. ASCII uses 7 bits to represent 128 characters including English letters, digits and symbols. Extended ASCII uses 8 bits for 256 characters. Unicode can represent characters from virtually all world languages using up to 32 bits, ensuring global consistency.
文本通过为每个字符分配一个唯一的二进制代码来存储。ASCII 使用 7 个比特表示 128 个字符，包括英文字母、数字和符号。扩展 ASCII 使用 8 个比特表示 256 个字符。Unicode 可以使用最多 32 个比特来表示几乎所有世界语言的字符，确保了全球一致性。
Images are made of tiny dots called pixels. In a bitmap, each pixel's colour is stored as a binary value. The colour depth (bits per pixel) determines how many distinct colours can be shown: 1 bit gives 2 colours, 8 bits give 256 colours, and 24 bits allow over 16 million colours. Metadata includes the image's width, height and colour depth.
图像由称为像素的微小点构成。在位图中，每个像素的颜色都存储为二进制值。颜色深度（每像素比特数）决定了可以显示多少种不同的颜色：1 比特显示 2 种颜色，8 比特显示 256 种颜色，24 比特可显示超过 1600 万种颜色。元数据包含图像的宽度、高度和颜色深度。
Sound is analogue in nature and must be converted into digital form by sampling. An analogue-to-digital converter (ADC) measures the amplitude of the sound wave at regular intervals. The sample rate (e.g. 44.1 kHz) indicates how many samples per second are taken. Higher sample rates and greater bit depths produce more accurate digital representations but increase file size.
声音本质上是模拟的，必须通过采样转换为数字形式。模数转换器（ADC）以固定间隔测量声波的振幅。采样率（例如 44.1 kHz）表示每秒采集多少样本。更高的采样率和更大的位深度可产生更精确的数字表示，但会增加文件大小。
6. Compression | 数据压缩
Compression reduces file size to save storage space and decrease transmission time. Lossless compression works by finding and eliminating statistical redundancy, allowing the original data to be perfectly reconstructed. It is essential for text files, programs and spreadsheets where every bit matters.
压缩通过减小文件大小来节省存储空间并减少传输时间。无损压缩通过寻找并消除统计冗余来工作，使得原始数据能够完美重建。它对于每个比特都至关重要的文本文件、程序和电子表格来说是必不可少的。
Lossy compression removes some of the data permanently, aiming to preserve perceived quality while achieving much greater space savings. It is commonly used for images (JPEG), audio (MP3) and video (MPEG). The trade-off is that some detail is lost and the original cannot be fully restored.
有损压缩会永久性地移除部分数据，旨在保持感知质量的同时实现更大的空间节省。它常用于图像（JPEG）、音频（MP3）和视频（MPEG）。其代价是会丢失一些细节，且无法完全恢复原始文件。
7. Network Basics | 网络基础
A network links two or more devices so they can share resources and communicate. A Local Area Network (LAN) covers a small geographical area like a school or office, often using Ethernet or Wi-Fi. A Wide Area Network (WAN) connects LANs across cities or countries; the Internet is the largest WAN.
网络连接两个或多个设备，使它们能够共享资源和通信。局域网（LAN）覆盖学校或办公室等较小地理区域，常使用以太网或 Wi-Fi。广域网（WAN）将跨城市或国家的局域网连接起来；互联网是最大的广域网。
Key hardware includes network interface cards (NICs), switches that connect devices within a LAN, routers that forward data between networks, and wireless access points. Data is broken into packets, each containing the source and destination addresses, a sequence number and error-checking information.
关键硬件包括网络接口卡（NIC）、在 LAN 内连接设备的交换机、在网络间转发数据包的路由器以及无线接入点。数据被分割为数据包，每个包含源地址和目的地址、序列号及错误校验信息。
Network topologies describe the layout. In a star topology, all devices connect to a central switch; if one cable fails, only that device is affected. In a mesh topology, devices are interconnected, offering high reliability. Protocols such as TCP/IP, HTTP, HTTPS, FTP, SMTP and IMAP define the rules for data transmission and communication services.
网络拓扑描述了布局。在星型拓扑中，所有设备连接到中央交换机；如果某根电缆故障，仅该设备受影响。在网状拓扑中，设备相互连接，提供了高可靠性。TCP/IP、HTTP、HTTPS、FTP、SMTP 和 IMAP 等协议定义了数据传输和通信服务的规则。
8. Network Security | 网络安全
Network security protects data from unauthorised access and attacks. Common threats include malware (viruses, worms, ransomware), phishing (fraudulent emails tricking users into revealing sensitive data), brute-force attacks (trying many passwords) and denial-of-service (DoS) attacks that overload a server with traffic.
网络安全保护数据免受未经授权的访问和攻击。常见威胁包括恶意软件（病毒、蠕虫、勒索软件）、网络钓鱼（诱骗用户泄露敏感数据的欺诈邮件）、暴力攻击（尝试大量密码）以及用流量压垮服务器的拒绝服务（DoS）攻击。
Defensive measures are critical. Firewalls monitor incoming and outgoing traffic, blocking suspicious packets. Encryption scrambles data so that it can only be read with the correct decryption key. Strong password policies, two-factor authentication and regular software updates significantly reduce vulnerability.
防御措施至关重要。防火墙监控进出流量，阻止可疑数据包。加密将数据打乱，只有使用正确的解密密钥才能读取。强密码策略、双因素认证和定期软件更新可显著降低脆弱性。
9. Algorithms and Computational Thinking | 算法与计算思维
Computational thinking involves breaking down complex problems using four cornerstones: decomposition (splitting a problem into smaller parts), pattern recognition (spotting similarities), abstraction (focusing on important details and ignoring irrelevant ones) and algorithm design (creating a step-by-step solution).
计算思维涉及使用四大基石来分解复杂问题：分解（将问题拆分为更小的部分）、模式识别（发现相似性）、抽象（专注于重要细节，忽略无关内容）以及算法设计（创建分步解决方案）。
Algorithms can be expressed as flowcharts or pseudocode. Flowcharts use standard symbols: ovals for start/stop, parallelograms for input/output, rectangles for processes, diamonds for decisions and arrows for flow direction. Pseudocode uses plain English with structured indentation, allowing it to be written without worrying about specific programming syntax.
算法可以用流程图或伪代码表示。流程图使用标准符号：椭圆形表示开始/停止，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，箭头表示流程方向。伪代码使用结构化缩进的简明英语，使其编写时无需担心特定编程语法。
Two essential search algorithms are linear search (checking each item in turn until the target is found) and binary search (repeatedly dividing a sorted list in half). A simple sort like bubble sort works by repeatedly stepping through the list, comparing adjacent items and swapping them if they are in the wrong order.
两种基本的搜索算法是线性搜索（逐一检查每个项目，直到找到目标）和二分搜索（不断将有序列表对半分）。像冒泡排序这样的简单排序算法，通过反复遍历列表、比较相邻项目并在它们顺序错误时交换它们来工作。
10. Programming Fundamentals | 编程基础
Variables are named memory locations that hold values which can change while a program runs. Common data types include integer (whole numbers), float (decimal numbers), string (text), and Boolean (true/false). Choosing the right data type ensures efficient memory use and prevents type errors.
变量是命名的内存位置，存有在程序运行时可以改变的值。常见数据类型包括整型（整数）、浮点型（小数）、字符串（文本）和布尔型（真/假）。选择正确的数据类型可确保高效利用内存并防止类型错误。
The three basic programming constructs are sequence, selection and iteration. Sequence means statements are executed one after another. Selection (if-else statements) allows the program to make decisions based on conditions. Iteration repeats a block of code; 'for' loops are used when the number of repetitions is known, while 'while' loops continue as long as a condition remains true.
三种基本编程结构是顺序、选择和迭代。顺序意味着语句一条接一条地执行。选择（if-else 语句）允许程序根据条件做出决策。迭代重复一个代码块；当重复次数已知时使用 'for' 循环，而 'while' 循环只要条件为真就会继续执行。
11. Ethical, Legal and Environmental Issues | 伦理、法律与环境问题
As technology pervades daily life, understanding its wider impact is vital. The Data Protection Act (2018) and the UK GDPR set rules for collecting, storing and using personal data, giving individuals rights over their information. Copyright law protects software and creative works from unauthorised copying.
随着技术渗透日常生活，理解其更广泛的影响至关重要。《2018 年数据保护法》和英国 GDPR 为收集、存储和使用个人数据制定了规则，赋予个人对其信息的权利。版权法保护软件和创意作品免遭未经授权的复制。
Computing also has an environmental footprint. Manufacturing devices consumes energy and scarce raw materials. E-waste often ends in landfill, releasing toxic substances. Data centres require huge amounts of electricity for power and cooling. Positive actions include recycling equipment, using energy-efficient hardware and promoting a circular economy.
计算机也有环境足迹。制造设备消耗能源和稀缺原材料。电子垃圾往往被填埋，释放有毒物质。数据中心需要大量电力进行供电和冷却。积极行动包括回收设备、使用节能硬件和促进循环经济。
The digital divide highlights the gap between those who have access to modern digital technology and those who do not. This inequality can affect education, employment and social inclusion. As a responsible computer user, you should consider accessibility needs, respect privacy and use technology in ways that benefit society.
数字鸿沟凸显了能够接触现代数字技术的人与无法接触者之间的差距。这种不平等可能影响教育、就业和社会包容。作为负责任的计算机用户，你应考虑无障碍需求，尊重隐私，并以有益于社会的方式使用技术。
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