📚 Year 11 CAIE Computer Science: Core Knowledge Review | Year 11 CAIE 计算机：核心知识点梳理
The CAIE IGCSE Computer Science (0478) syllabus covers essential concepts from the fundamentals of data representation to programming and cybersecurity. This article organises the core knowledge areas for Year 11 students, presenting each topic with concise explanations in both English and Chinese for effective bilingual revision.
CAIE IGCSE 计算机科学（0478）课程涵盖了从数据表示基础到编程与网络安全的必要概念。本文为 Year 11 学生梳理核心知识领域，每个主题都以英中双语简明解释，便于有效复习。
1. Data Representation | 数据表示
Computers store and process data in binary form – using 0s and 1s – because their circuits can easily represent two states (on/off). All numbers, text, images and sound are ultimately encoded as binary.
计算机以二进制形式（0 和 1）存储和处理数据，因为其电路可以轻松表示两种状态（开/关）。所有数字、文本、图像和声音最终都被编码为二进制。
2¹ + 1×2⁰ = 11₁₀). Denary to binary: repeatedly divide by 2 and read remainders backwards.
二进制转十进制：将每一位乘以其位值（例如 1011₂ = 1×2³ + 0×2² + 1×2¹ + 1×2⁰ = 11₁₀）。十进制转二进制：反复除以 2，逆序读取余数。
Hexadecimal (base 16) simplifies long binary strings. Each hex digit represents 4 bits (nibble). Values 10–15 use A–F. Conversion between hex and binary is straightforward: group bits in fours.
十六进制（基数为 16）简化了长二进制串。每一个十六进制数字代表 4 个比特（半字节）。数值 10–15 使用 A–F。十六进制与二进制之间的转换很简单：将二进制每四位一组。
Text is represented using character sets such as ASCII (7 bits) and Unicode. Images are stored as a grid of pixels, each with a colour value. Sound is sampled at regular intervals and stored as binary numbers; higher sampling rate and bit depth give better quality but larger files.
文本使用字符集表示，如 ASCII（7 位）和 Unicode。图像存储为像素网格，每个像素有颜色值。声音按固定间隔采样并以二进制数字存储；采样率和位深度越高，音质越好但文件越大。
ight × colour depth. Sound size = sample rate × bit depth × duration (seconds) × channels.
文件大小估算：文本文件大小（比特）= 字符数 × 每个字符的位数。图像大小 = 宽度 × 高度 × 颜色深度。声音大小 = 采样率 × 位深度 × 持续时间（秒）× 声道数。
2. Data Transmission | 数据传输
Data can be transmitted between devices using serial or parallel communication. Serial sends one bit at a time over a single wire, suitable for long distances (e.g., USB). Parallel sends multiple bits simultaneously but suffers from skew over longer cables.
数据可以在设备之间通过串行或并行通信传输。串行每次通过一根线发送一个比特，适合长距离传输（如 USB）。并行同时发送多个比特，但在较长线缆上会出现时钟偏移问题。
Transmission can be simplex (one-way), half-duplex (both ways but not at the same time) or full-duplex (both ways simultaneously). USB uses half-duplex or full-duplex modes.
传输可以是单工（单向）、半双工（双向但不同时）或全双工（同时双向）。USB 使用半双工或全双工模式。
Error detection is vital. Parity bits (odd/even parity) detect single-bit errors. Checksums use addition of data blocks to generate a check value; the receiver recalculates and compares. More advanced methods like CRC and echo checks are also used.
错误检测至关重要。奇偶校验位（奇/偶校验）可检测单比特错误。校验和通过将数据块相加生成一个校验值；接收端重新计算并比较。还使用更先进的方法如 CRC 和回声检查。
Encryption protects data during transmission. Symmetric encryption uses the same key to encrypt and decrypt; asymmetric encryption (e.g., public/private key pairs) is more secure but slower. SSL/TLS secures web traffic.
加密保护传输中的数据。对称加密使用相同的密钥进行加密和解密；非对称加密（如公钥/私钥对）更安全但较慢。SSL/TLS 保护网络通信。
3. Computer Networks | 计算机网络
A network connects computers to share resources. LANs (Local Area Networks) cover a small area; WANs (Wide Area Networks) cover large geographical distances. The internet is a global WAN.
网络将计算机连接起来以共享资源。局域网（LAN）覆盖较小区域；广域网（WAN）覆盖较大地理距离。互联网是一个全球性的广域网。
Common network topologies: star (all devices connect to a central switch), bus (all share a single cable), mesh (devices interconnected) and hybrid. Star topology is popular because failure of one cable does
Published by TutorHao | Year 11 Computer Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图