📚 Core Knowledge Review for Year 9 CAIE Computer Science | Year 9 CAIE 计算机：核心知识点梳理
The Year 9 CAIE Computer Science curriculum introduces students to the foundational concepts of computing, covering both theoretical knowledge and practical programming skills. This stage builds a solid base for IGCSE studies by exploring how computers work, how data is represented, how networks connect the world, and how to think algorithmically.
Year 9 CAIE 计算机课程向学生介绍计算的基础概念，涵盖理论知识和实践编程技能。本阶段通过探索计算机工作原理、数据表示方式、网络如何连接世界以及如何运用算法思维，为 IGCSE 学习打下坚实基础。
1. Computer Systems: Hardware and Software | 计算机系统：硬件与软件
A computer system consists of hardware and software. Hardware refers to the physical components you can touch, such as the processor, memory, and input/output devices. Software includes the programs and data that instruct the hardware. Without software, hardware cannot perform useful tasks.
计算机系统由硬件和软件组成。硬件指可触摸的物理部件，如处理器、存储器和输入/输出设备。软件包括指示硬件工作的程序和数据。没有软件，硬件就无法完成有用的任务。
The central processing unit (CPU) is the 'brain' of the computer. It processes instructions by following the fetch–decode–execute cycle. The CPU's speed is measured in gigahertz (GHz).
中央处理器 (CPU) 是计算机的“大脑”。它通过取指令—译码—执行周期来处理指令。CPU 的速度以吉赫兹 (GHz) 为单位计量。
Software is divided into system software (like operating systems) and application software (like word processors and games). The operating system manages hardware resources and provides a user interface.
软件分为系统软件（如操作系统）和应用软件（如文字处理程序和游戏）。操作系统管理硬件资源并提供用户界面。
2. Input and Output Devices | 输入与输出设备
Input devices allow users to enter data into a computer. Common examples include keyboards, mice, touchscreens, microphones, and barcode scanners. Each device captures a specific type of data, such as text, coordinates, or audio.
输入设备允许用户将数据输入计算机。常见例子包括键盘、鼠标、触摸屏、麦克风和条形码扫描器。每种设备捕捉特定类型的数据，如文本、坐标或音频。
Output devices display or produce the results of computer processing. Monitors, printers, speakers, and projectors are typical output devices. A monitor displays visual output, while a printer produces hard copies.
输出设备显示或产生计算机处理的结果。显示器、打印机、扬声器和投影仪是典型的输出设备。显示器显示视觉输出，而打印机制作硬拷贝。
Some devices serve both input and output functions, such as a touchscreen or a network interface card. This dual role makes them versatile in modern computing.
某些设备兼具输入和输出功能，例如触摸屏或网络接口卡。这种双重角色使它们在现代计算中非常通用。
3. Storage and Memory | 存储与内存
Memory (RAM, Read-Only Memory) holds data temporarily or permanently. RAM is volatile memory that stores data and programs currently in use; when power is turned off, its contents are lost. ROM is non-volatile and typically stores firmware, such as the boot instructions.
存储器（RAM，只读存储器）临时或永久保存数据。RAM 是易失性存储器，存储当前正在使用的数据和程序；断电后其内容会丢失。ROM 是非易失性存储器，通常存放固件，如启动指令。
Secondary storage devices, like HDDs, SSDs, and USB flash drives, provide long-term data storage. Unlike RAM, these devices retain data even when the computer is switched off. Storage capacity is measured in bytes (GB, TB).
辅助存储设备，如硬盘驱动器 (HDD)、固态硬盘 (SSD) 和 U 盘，提供长期数据存储。与 RAM 不同，这些设备即使在计算机关闭时也能保留数据。存储容量以字节 (GB, TB) 为单位计量。
Optical discs (CD, DVD, Blu-ray) use laser technology to read and write data. They are less common today but are still used for media distribution.
光盘（CD、DVD、蓝光）使用激光技术读写数据。它们今天不太常见，但仍用于媒体分发。
4. System Software and Application Software | 系统软件与应用软件
System software manages the computer's hardware and provides a platform for running applications. The operating system (OS) is the most important system software. Examples include Windows, macOS, Linux, and Android.
系统软件管理计算机硬件，并为运行应用程序提供平台。操作系统 (OS) 是最重要的系统软件。例子包括 Windows、macOS、Linux 和 Android。
Utility software performs maintenance tasks, such as antivirus scanning, disk defragmentation, and backup. These tools help keep the system secure and efficient.
实用程序软件执行维护任务，如防病毒扫描、磁盘碎片整理和备份。这些工具有助于保持系统的安全性和高效性。
Application software allows users to perform specific tasks, such as creating documents (word processors), editing images (graphics software), or browsing the web (browsers). Apps are designed to meet user needs.
应用软件允许用户执行特定任务，如创建文档（文字处理软件）、编辑图像（图形软件）或浏览网页（浏览器）。应用程序旨在满足用户需求。
5. Data Representation: Binary and Bits | 数据表示：二进制与位
Computers store and process all data as binary digits (bits), which are 0s and 1s. A group of 8 bits is called a byte. Everything from numbers, text, images, and sound is represented using binary patterns.
计算机以二进制数字（位，比特）即 0 和 1 来存储和处理所有数据。8 个位组成一个字节。从数字、文本、图像到声音，一切均用二进制模式表示。
The denary number system (base 10) uses digits 0– ower of 2. For example, the binary number 1101₂ equals 1×2³+1×2²+0×2¹+1×2⁰ = 13 in denary.
十进制数制（基数为 10）使用数字 0–9，而二进制使用基数为 2。将二进制转换为十进制时，每个位的位置代表 2 的幂。例如，二进制数 1101₂ 等于 1×2³+1×2²+0×2¹+1×2⁰ = 十进制 13。
Text is encoded using standards like ASCII and Unicode. Each character is assigned a unique binary code. Images are represented as a grid of pixels, where each pixel's colour is stored as binary.
文本使用 ASCII 和 Unicode 等标准编码。每个字符分配有一个唯一的二进制代码。图像表示为一个像素网格，每个像素的颜色以二进制形式存储。
6. Introduction to Computer Networks | 计算机网络导论
A computer network is a group of interconnected devices that can share resources and communicate. Networks can be classified by size: a Local Area Network (LAN) covers a small area like a school or office, while a Wide Area Network (WAN) connects larger geographical areas, such as the Internet.
计算机网络是一组互联的设备，可以共享资源和通信。网络可按规模分类：局域网 (LAN) 覆盖较小区域，如学校或办公室；而广域网 (WAN) 连接更大的地理区域，如互联网。
Networks require hardware like switches, routers, and network interface cards (NICs). A switch forwards data within a LAN, while a router connects different networks together, directing data packets to their destinations.
网络需要交换机、路由器和网卡 (NIC) 等硬件。交换机在局域网内转发数据，而路由器将不同网络连接起来，将数据包导向目的地。
Network topologies describe how devices are arranged. Common topologies include star, bus, and ring. In a star topology, all devices connect to a central switch; failure of one cable does not affect the rest.
网络拓扑描述设备的排列方式。常见拓扑包括星型、总线型和环型。在星型拓扑中，所有设备连接到中央交换机；一条电缆故障不会影响其他设备。
7. The Internet and the World Wide Web | 互联网与万维网
The Internet is a global network of networks that connects millions of computers. It uses a set of protocols called TCP/IP to ensure data can travel reliably. Every device on the Internet has an IP address, which identifies it uniquely.
互联网是一个网络之网，将数百万台计算机连接在一起。它使用一套称为 TCP/IP 的协议来确保数据可靠传输。互联网上的每台设备都有一个 IP 地址，用于唯一标识。
The World Wide Web (WWW) is a service that runs on the Internet. It consists of web pages written in HTML and accessed via web browsers using URLs. The Web is not the same as the Internet; it is one of many services that use the Internet, such as email and file transfer.
万维网 (WWW) 是运行在互联网上的一项服务。它由用 HTML 编写的网页组成，并通过 Web 浏览器使用 URL 访问。万维网不等同于互联网；它是使用互联网的众多服务之一，其他还有电子邮件和文件传输。
A URL (Uniform Resource Locator) is the address of a web page, e.g., https://www.example.com. It includes the protocol (https), the domain name, and the path to a specific resource.
URL（统一资源定位符）是网页的地址，例如 https://www.example.com。它包括协议 (https)、域名以及特定资源的路径。
8. Network Security and Online Safety | 网络安全与在线安全
Network security involves protecting data and systems from unauthorised access, attacks, and damage. Common threats include malware (viruses, worms, trojans), phishing, and denial-of-service attacks. Firewalls monitor and control incoming and outgoing network traffic based on security rules.
网络安全涉及保护数据和系统免受未经授权的访问、攻击和破坏。常见威胁包括恶意软件（病毒、蠕虫、特洛伊木马）、网络钓鱼和拒绝服务攻击。防火墙根据安全规则监控和控制网络流量进出。
Encryption scrambles data so that only authorised parties can read it. When you visit a secure website (https), the communication is encrypted using protocols like SSL/TLS, protecting sensitive information such as passwords and credit card numbers.
加密将数据打乱，只有经过授权的一方才能读取。当您访问安全网站 (https) 时，通信会使用 SSL/TLS 等协议加密，保护密码和信用卡号等敏感信息。
Online safety practices include using strong passwords, not sharing personal information with strangers, and being cautious about downloading attachments or clicking links. Users should also regularly update software to patch security vulnerabilities.
在线安全实践包括使用强密码、不与陌生人分享个人信息、谨慎下载附件或点击链接。用户还应定期更新软件以修补安全漏洞。
9. Programming Fundamentals: Algorithms and Pseudocode | 编程基础：算法与伪代码
An algorithm is a step-by-step procedure to solve a problem or perform a task. Algorithms can be expressed in natural language, flowcharts, or pseudocode. They consist of sequence, selection, and iteration.
算法是解决某个问题或执行某项任务的逐步步骤。算法可以用自然语言、流程图或伪代码表示。它们由顺序、选择和迭代组成。
Pseudocode is a simple way of writing algorithms that resembles a programming language but is meant for human reading. It uses keywords like INPUT, OUTPUT, IF…THEN…ELSE, and WHILE loops.
伪代码是一种编写算法的简单方式，类似编程语言但供人阅读。它使用诸如 INPUT、OUTPUT、IF…THEN…ELSE 和 WHILE 循环等关键词。
Flowcharts use standard symbols: ovals for start/end, rectangles for processes, diamonds for decisions, and arrows for flow of control. Tracing a flowchart helps understand how an algorithm works step by step.
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，箭头表示控制流。跟踪流程图有助于逐步理解算法如何工作。
10. Programming Concepts: Variables, Loops, and Conditionals | 编程概念：变量、循环与条件
Variables are named storage locations in a program that hold data which can
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