📚 Complete Computer Science for Cambridge IGCSE & O Level: Core Concepts | 剑桥 IGCSE 与 O Level 计算机科学核心概念解析
This revision guide distils key topics from Complete Computer Science for Cambridge IGCSE & O Level by Alison Page and David Waters. It focuses on the core knowledge and skills tested in CIE IGCSE Computer Science (0478) and O Level Computer Science (2210), including data representation, hardware, software, networks, security, algorithms, programming, logic gates and databases. Each section pairs an English explanation with a Chinese translation to support bilingual learners.
本复习指南提炼了 Alison Page 与 David Waters 所著 Complete Computer Science for Cambridge IGCSE & O Level 的核心主题。它聚焦 CIE IGCSE 计算机科学（0478）和 O Level 计算机科学（2210）考试所考查的核心知识与技能，涵盖数据表示、硬件、软件、网络、安全、算法、编程、逻辑门和数据库。每节都采用英文解释与中文译文配对的形式，以帮助双语学习者。
1. Data Representation | 数据表示
Data representation is the foundation of all computer systems. Computers store and process information as binary digits (bits), where a single bit is either 0 or 1. A group of 8 bits forms a byte, which can represent 256 different values. Text characters are commonly encoded using ASCII or Unicode. Sound is sampled at regular intervals and stored as binary values; images are represented as a grid of pixels, each with a binary colour value.
数据表示是所有计算机系统的基础。计算机以二进制数字（比特）存储和处理信息，单个比特只能是 0 或 1。8 个比特组成一个字节，可以表示 256 种不同的值。文本字符通常使用 ASCII 或 Unicode 编码。声音按固定间隔采样并以二进制值存储；图像表示为像素网格，每个像素都有二进制颜色值。
umn values where a 1 appears. For example, 01001101₂ equals 64 + 8 + 4 + 1 = 77 in denary.
二进制数制使用基数 2，这意味着从右到左每列的位权依次为 1、2、4、8、16、32、64 和 128。要将二进制数转换为十进制，只需将出现 1 的列值相加。例如，01001101₂ 等于 64 + 8 + 4 + 1 = 77（十进制）。
2. Binary Arithmetic & Hexadecimal | 二进制运算与十六进制
ts exceeds 1, a carry is passed to the next most significant bit. This process is essential for arithmetic operations inside the ALU.
二进制加法遵循与十进制相同的进位规则。四条基本规则为：0 + 0 = 0；0 + 1 = 1；1 + 0 = 1；1 + 1 = 0 进 1。当两个比特之和超过 1 时，会向更高有效位产生进位。这一过程对于 ALU 内部的算术运算至关重要。
Example: 1010₂ + 0110₂ = 10000₂
Hexadecimal (base 16) uses digits 0-9 and letters A-F to represent values 10-15. Each hexadecimal digit corresponds exactly to four bits (a nibble). This makes long binary strings much easier for humans to read and write. Conversion between denary, binary and hexadecimal is a required exam skill.
十六进制（基数为 16）使用数字 0-9 和字母 A-F 表示值 10-15。每个十六进制数字恰好对应四个比特（半字节）。这使得长二进制串更易于人类读写。十进制、二进制和十六进制之间的转换是考试的必备技能。
3. Computer Architecture | 计算机体系结构
The von Neumann architecture describes a stored-program computer in which data and instructions share the same memory. Key components include the central processing unit (CPU), main memory, input/output devices and the system bus. The CPU contains the control unit (CU), arithmetic logic unit (ALU), registers and cache. The fetch-decode-execute cycle is the process by which the CPU retrieves an instruction from memory, decodes it and carries it out.
冯·诺依曼体系结构描述了一种存储程序计算机，其中数据和指令共享同一存储器。关键组件包括中央处理器（CPU）、主存储器、输入/输出设备和系统总线。CPU 包含控制单元（CU）、算术逻辑单元（ALU）、寄存器和高速缓存。取指-译码-执行周期是 CPU 从存储器中取出指令、译码并执行的过程。
Registers such as the program counter (PC), memory address register (MAR), memory data register (MDR) and accumulator (ACC) have specific roles in the cycle. The system bus consists of the address bus, data bus and control bus, each carrying different information between components.
程序计数器（PC）、存储器地址寄存器（MAR）、存储器数据寄存器（MDR）和累加器（ACC）等寄存器在该周期中发挥特定作用。系统总线由地址总线、数据总线和控制总线组成，每条总线在组件之间传输不同的信息。
4. Input and Output Devices | 输入与输出设备
Input devices convert physical data into a form the computer can process. Common examples include keyboards, mice, microphones, scanners, barcode readers and sensors such as temperature, light and motion detectors. Output devices present processed data to the user, such as monitors, printers, speakers and actuators. Touchscreens combine both input and output functions in a single device.
输入设备将物理数据转换为计算机可以处理的形式。常见例子包括键盘、鼠标、麦克风、扫描仪、条形码阅读器和传感器（如温度、光线和运动探测器）。输出设备将处理后的数据呈现给用户，如显示器、打印机、扬声器和执行器。触摸屏在单一设备中兼具输入和输出功能。
When choosing an input or output device, factors such as speed, accuracy, cost, environment, durability and user needs must be considered. For example, a barcode reader is fast and accurate in a supermarket checkout, while a keyboard is more suitable for text entry in an office.
选择输入或输出设备时，必须考虑速度、准确性、成本、环境、耐用性和用户需求等因素。例如，条形码阅读器在超市收银台快速且准确，而键盘更适合办公室的文本输入。
5. Memory and Storage | 存储器与存储设备
Primary memory includes random access memory (RAM) and read-only memory (ROM). RAM is volatile working memory that holds data and programs currently in use; ROM is non-volatile and stores firmware such as BIOS or bootstrap loaders. Secondary storage is non-volatile and retains data when power is off. Magnetic hard disks, solid-state drives (SSDs), optical discs and USB flash drives each offer different capacity, speed, portability and durability trade-offs.
主存储器包括随机存取存储器（RAM）和只读存储器（ROM）。RAM 是易失性工作存储器，保存当前正在使用的数据和程序；ROM 是非易失性的，存储固件，如 BIOS 或引导加载程序。辅助存储器是非易失性的，在断电时保留数据。磁性硬盘、固态硬盘（SSD）、光盘和 USB 闪存盘在容量、速度、便携性和耐用性方面各有不同的权衡。
Virtual memory uses part of secondary storage as an extension of RAM when there is insufficient physical memory. This allows larger programs to run but can slow performance because accessing secondary storage is much slower than accessing RAM.
虚拟内存使用辅助存储器的一部分作为 RAM 的扩展，当物理内存不足时使用。这允许运行更大的程序，但可能会降低性能，因为访问辅助存储器的速度远慢于访问 RAM。
6. System Software and Operating Systems | 系统软件与操作系统
System software manages hardware and provides a platform for application software. The operating system (OS) performs essential functions: memory management, process scheduling, file management, device driver management, user interface provision and security enforcement. Examples include Windows, macOS, Linux, Android and iOS. Without an OS, users would need to manage hardware resources manually, which is inefficient and error-prone.
系统软件管理硬件并为应用软件提供平台。操作系统（OS）执行基本功能：内存管理、进程调度、文件管理、设备驱动程序管理、用户界面提供和安全性实施。示例包括 Windows、macOS、Linux、Android 和 iOS。没有操作系统，用户将需要手动管理硬件资源，这既低效又容易出错。
Utility software performs maintenance tasks such as disk defragmentation, backup, compression, antivirus scanning and file recovery. These tools help keep the system efficient, secure and reliable.
实用软件执行维护任务，如磁盘碎片整理、备份、压缩、防病毒扫描和文件恢复。这些工具有助于保持系统高效、安全和可靠。
7. Networks and the Internet | 网络与互联网
A computer network is two or more devices connected to share resources and communicate. Networks can be classified by geographical size: local area network (LAN), wide area network (WAN), and personal area network (PAN). Network topologies include star, bus, ring and mesh. Common protocols such as TCP/IP, HTTP, HTTPS, FTP and SMTP define rules for data transmission. The Internet is a global WAN that uses packet switching to route data across interconnected networks.
计算机网络是两个或多个连接起来以共享资源和通信的设备。网络可按地理范围分类：局域网（LAN）、广域网（WAN）和个人区域网（PAN）。网络拓扑包括星型、总线型、环型和网状型。诸如 TCP/IP、HTTP、HTTPS、FTP 和 SMTP 等常见协议定义了数据传输规则。互联网是一个全球性广域网，使用分组交换在互连网络之间路由数据。
Networking hardware includes routers, switches, network interface cards (NICs), modems and wireless access points. Each device performs a specific role in directing, switching or transmitting data between nodes.
网络硬件包括路由器、交换机、网络接口卡（NIC）、调制解调器和无线接入点。每台设备在节点之间定向、交换或传输数据方面发挥着特定作用。
8. Cyber Security and Ethics | 网络安全与伦理
Cyber security protects systems, networks and data from digital attacks. Key threats include malware (viruses, worms, trojans, ransomware), phishing, denial-of-service (DoS) attacks and social engineering. Protective measures include firewalls, encryption, strong passwords, two-factor authentication, antivirus software and regular updates. Students must understand both technical and social implications of these threats.
网络安全保护系统、网络和数据免受数字攻击。主要威胁包括恶意软件（病毒、蠕虫、木马、勒索软件）、网络钓鱼、拒绝服务（DoS）攻击和社会工程学。防护措施包括防火墙、加密、强密码、双重身份验证、防病毒软件和定期更新。学生必须理解这些威胁的技术和社会影响。
Ethical issues involve data privacy, acceptable use policies, copyright, plagiarism and the digital divide. Computing professionals and users must act responsibly, respect intellectual property and ensure that technology does not widen social inequality.
伦理问题涉及数据隐私、可接受使用政策、版权、剽窃和数字鸿沟。计算机专业人员和用户必须负责任地行事，尊重知识产权，并确保技术不会扩大社会不平等。
9. Algorithm Design and Pseudocode | 算法设计与伪代码
An algorithm is a step-by-step procedure for solving a problem. Algorithm design tools include flowcharts and pseudocode. Pseudocode uses structured English statements such as INPUT, OUTPUT, IF...THEN...ELSE...ENDIF, FOR...TO...NEXT, WHILE...DO...ENDWHILE and REPEAT...UNTIL. Trace tables are used to record variable changes during dry runs, helping to identify logic errors. Efficient algorithms minimise time and memory use.
算法是解决问题的逐步过程。算法设计工具包括流程图和伪代码。伪代码使用结构化英语语句，如 INPUT、OUTPUT、IF...THEN...ELSE...ENDIF、FOR...TO...NEXT、WHILE...DO...ENDWHILE 和 REPEAT...UNTIL。跟踪表用于记录手工运行期间变量的变化，帮助识别逻辑错误。高效算法能最大限度地减少时间和内存使用。
Example: Total ← 0; FOR Count ← 1 TO 10; Total ← Total + Count; NEXT; OUTPUT Total
Flowcharts use standard symbols: ovals for start/end, parallelograms for input/output, rectangles for processes, diamonds for decisions and arrows for flow direction. Both pseudocode and flowcharts are accepted in CIE exams, but they must be consistent and unambiguous.
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，菱形表示判断，箭头表示流程方向。CIE 考试中伪代码和流程图均可接受，但必须一致且无歧义。
10. Programming Concepts | 编程概念
Programming languages are classified as high-level or low-level. High-level languages (Python, Java, C++) use English-like syntax and are portable across platforms; low-level languages include assembly language and machine code, which are closer to hardware and less portable. Key programming constructs are sequence, selection (if statements) and iteration (for, while loops). Variables, constants, data types (integer, real, char, string, boolean) and arrays are fundamental concepts.
编程语言分为高级语言和低级语言。高级语言（Python、Java、C++）使用类似英语的语法且可跨平台移植；低级语言包括汇编语言和机器代码，它们更接近硬件且可移植性较差。关键编程结构是顺序、选择（if 语句）和迭代（for、while 循环）。变量、常量、数据类型（整数、实数、字符、字符串、布尔值）和数组是基本概念。
Procedural programming breaks programs into functions or procedures that can be reused and tested independently. This improves code readability, maintainability and reliability. Array indices typically start at 0 or 1 depending on the language; in Cambridge pseudocode, arrays are often indexed from 1.
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