📚 Core Knowledge Revision for Year 11 CAIE Computer Science | Year 11 CAIE 计算机：核心知识点梳理
This revision guide covers the essential topics for the CAIE IGCSE Computer Science (0478) syllabus, designed specifically for Year 11 students preparing for their final examinations. Each section summarises key concepts with clear English explanations followed by a matching Chinese version, helping bilingual learners consolidate understanding and recall facts efficiently.
本复习指南涵盖 CAIE IGCSE 计算机科学 (0478) 考纲的核心主题，专门为准备最终考试的 Year 11 学生设计。每个部分总结关键概念，先提供清晰的英文说明，然后是相应的中文版本，帮助双语学习者巩固理解并高效回忆知识点。
1. Number Systems: Binary, Denary and Hexadecimal | 数字系统：二进制、十进制与十六进制
Computers use binary (base‑2) because all data must be represented as two states: 0 and 1, corresponding to low and high voltages in digital circuits. Denary (base‑10) is the number system we use in everyday life, while hexadecimal (base‑16) provides a more human‑friendly way to represent long binary strings, often used for colour codes and memory addresses.
计算机使用二进制（基数为2），因为所有数据必须以两种状态表示：0 和 1，对应数字电路中的低电平和高电平。十进制（基数为10）是我们日常生活中使用的数字系统，而十六进制（基数为16）提供了一种更易读的方式来表示长二进制串，常用于颜色代码和内存地址。
y to binary uses repeated division by 2, reading remainders backwards. Binary to hexadecimal: group bits in fours from the right, then convert each nibble (4‑ e able to convert denary directly to hex by going via binary or repeatedly dividing by 16.
在这些系统之间进行转换是一项关键技能。二进制转十进制：将出现 1 的位值相加（例如 1011₂ = 8+0+2+1 = 11₁₀）。十进制转二进制使用反复除以 2 的方法，逆序读取余数。二进制转十六进制：从右侧开始将比特每四位一组，然后将每个半字节（4 比特组）转换为对应的十六进制数字（例如 1101 0111₂ = D7₁₆）。你还必须能够通过先转二进制或反复除以 16 的方式，直接从十进制转换为十六进制。
2. Data Storage and File Sizes | 数据存储与文件大小
e kibibyte (KiB = 1024 bytes), mebibyte (MiB), gibibyte (GiB) and so on. Be aware that storage manufacturers sometimes use decimal units (1 KB = 1000 bytes), but CAIE expects you to know the binary definitions: 1 KiB = 2¹⁰ bytes.
计算机内部的所有数据都以比特序列的形式存储。8 个比特组成一个字节，可以表示 2⁸ = 256 个不同的值。更大的单位包括 kibibyte（KiB = 1024 字节）、mebibyte（MiB）、gibibyte（GiB）等。请注意，存储设备制造商有时使用十进制单位（1 KB = 1000 字节），但 CAIE 期望你知道二进制定义：1 KiB = 2¹⁰ 字节。
File compression reduces storage space and transmission time. Lossless compression (e.g., run‑length encoding, Huffman coding) preserves every bit of original data; it is essential for text and program files. Lossy compression (e.g., JPEG for images, MP3 for audio) permanently discards some data that the human senses are less likely to notice, achieving much smaller file sizes but with some loss of quality.
文件压缩可减少存储空间和传输时间。无损压缩（例如游程编码、霍夫曼编码）会保留原始数据的每一个比特；对于文本和程序文件至关重要。有损压缩（例如图像的 JPEG、音频的 MP3）会永久丢弃部分人类感官不易察觉的数据，从而大大缩小文件体积，但会损失一些质量。
3. Computer Architecture: CPU and Fetch‑Decode‑Execute Cycle | 计算机体系结构：CPU 与取指-译码-执行周期
The central processing unit (CPU) is the ‘brain’ of the computer. It consists of the control unit (CU), arithmetic logic unit (ALU), registers (such as program counter, memory address register, memory data register, accumulator) and buses (address, data, control). The purpose of the CPU is to process instructions and data.
中央处理器（CPU）是计算机的“大脑”。它由控制单元（CU）、算术逻辑单元（ALU）、寄存器（如程序计数器、内存地址寄存器、内存数据寄存器、累加器）以及总线（地址总线、数据总线、控制总线）组成。CPU 的目的是处理指令和数据。
The fetch‑decode‑execute cycle is the fundamental process by which the CPU operates. In the fetch stage, the address from the program counter is placed on the address bus, the instruction is read from memory and stored in the memory data register, then copied to the current instruction register while the program counter increments. During decode, the control unit interprets the opcode. In the execute stage, the ALU performs the required operation, possibly using the accumulator. This cycle repeats billions of times per second.
取指-译码-执行周期是 CPU 运作的基本过程。在取指阶段，程序计数器中的地址被放到地址总线上，从内存中读取指令并存入内存数据寄存器，然后复制到当前指令寄存器，同时程序计数器递增。在译码阶段，控制单元解释操作码。在执行阶段，ALU 执行所需的操作，可能用到累加器。这个周期每秒钟重复数十亿次。
Factors affecting CPU performance include clock speed (frequency, measured in Hz), number of cores and cache memory size. More cores allow parallel processing, while cache provides high‑speed access to frequently used instructions and data.
影响 CPU 性能的因素包括时钟频率（频率，以赫兹为单位）、核心数量和高速缓存大小。核心数量增多允许并行处理，而高速缓存为常用指令和数据提供高速访问。
4. Input and Output Devices | 输入和输出设备
Input devices feed data into a computer system. Examples include keyboard, mouse, touchscreen, microphone, barcode scanner, QR code scanner, digital camera, and sensors (temperature, pressure, light, etc.). Each device translates a physical action into digital signals. Automatic data capture technologies like barcodes and RFID reduce human error and speed up data entry.
输入设备将数据馈入计算机系统。例子包括键盘、鼠标、触摸屏、麦克风、条形码扫描仪、二维码扫描仪、数码相机以及传感器（温度、压力、光线等）。每种设备将物理动作转换为数字信号。条形码和 RFID 等自动数据采集技术减少了人为错误并加快了数据输入速度。
Output devices present the processed information back to the user or control external machinery. Common output devices are monitors (LCD, LED), printers (inkjet, laser, 3D), speakers, headphones, and actuators (motors, relays). When choosing a device, factors such as speed, resolution, colour fidelity and running cost must be considered.
输出设备将处理后的信息呈现给用户或控制外部机械。常见的输出设备包括显示器（LCD、LED）、打印机（喷墨、激光、3D）、扬声器、耳机以及执行器（电机、继电器）。在选择设备时，必须考虑速度、分辨率、色彩保真度和运行成本等因素。
5. Memory and Storage | 内存与存储器
Primary memory directly accessible by the CPU is divided into RAM (random access memory) and ROM (read‑only memory). RAM is volatile — it loses its contents when power is removed — and holds currently running programs, data and parts of the OS. ROM is non‑volatile and typically stores the boot program (BIOS) needed to start the computer. RAM usually has higher capacity than ROM in modern systems.
CPU 可直接访问的主存储器分为 RAM（随机存取存储器）和 ROM（只读存储器）。RAM 是易失性的——断电后内容丢失——它保存当前运行的程序、数据和部分操作系统。ROM 是非易失性的，通常存储启动计算机所需的引导程序（BIOS）。在现代系统中，RAM 的容量通常大于 ROM。
Secondary storage is non‑volatile and used for long‑term data retention. Magnetic storage (HDD) uses spinning platters and read/write heads; it offers large capacity at low cost per gigabyte but is slower and susceptible to physical damage. Solid‑state storage (SSD, USB flash drives) uses NAND flash memory without moving parts, providing faster access, lower power consumption and greater durability, albeit at a higher price. Optical storage (CD, DVD, Blu‑ray) uses lasers to read pits on a reflective surface and is now mostly used for media distribution and archiving.
辅助存储器是非易失性的，用于长期保存数据。磁存储（HDD）使用旋转的盘片和读写磁头；它提供大容量且每 GB 成本较低，但速度较慢且容易受到物理损坏。固态存储（SSD、USB 闪存驱动器）使用 NAND 闪存，没有移动部件，提供更快的访问速度、更低的功耗和更好的耐用性，但价格更高。光存储（CD、DVD、蓝光）使用激光读取反射面上的凹坑，现在主要用于媒体分发和归档。
6. Networks and the Internet | 网络与互联网
A computer network is formed when two or more devices are connected to share resources and communicate. Networks can be classified by scale: LAN (local area network) covers a small geographical area such as a school or building; WAN (wide area network) spans large distances, often using telecommunication links. The internet is a global WAN.
计算机网络由两个或更多设备连接而成，以共享资源和通信。网络可按规模分类：LAN（局域网）覆盖学校或建筑物等小范围地理区域；WAN（广域网）跨越较大距离，通常使用电信链路。互联网是一个全球范围的 WAN。
Common network hardware includes router (forwards data packets between networks), switch (connects devices in a LAN and forwards frames based on MAC addresses), modem (converts digital signals to analogue for transmission over telephone lines), network interface card (NIC), and wireless access point. Transmission media can be copper cable (Ethernet), fibre optic (high speed, immune to interference) or wireless (Wi‑Fi, Bluetooth).
常见的网络硬件包括路由器（在网络之间转发数据包）、交换机（在 LAN 中连接设备并根据 MAC 地址转发帧）、调制解调器（将数字信号转换为模拟信号以便通过电话线传输）、网络接口卡（NIC）和无线接入点。传输介质可以是铜缆（以太网）、光纤（高速、抗干扰）或无线（Wi-Fi、蓝牙）。
Network topologies define the layout of connections. In a star topology, all devices connect to a central switch; it is easy to add devices and faults are isolated, but if the central switch fails the whole network goes down. In a mesh topology, devices have multiple connections, offering excellent redundancy but at higher cost. Hybrid topologies combine elements of both.
网络拓扑结构定义了连接的布局。在星型拓扑中，所有设备都连接到一个中央交换机；容易添加设备且故障隔离，但如果中央交换机故障，整个网络就会瘫痪。在网状拓扑中，设备之间有多条连接，提供出色的冗余，但成本较高。混合拓扑结合了两者的元素。
7. Network Security: Threats and Prevention | 网络安全：威胁与防范
Network security protects data and systems from unauthorised access, disruption, or damage. Key threats include malware (viruses, worms, Trojan horses), phishing (fraudulent emails seeking personal data), denial‑of‑service (DoS) attacks that flood a server with traffic, and brute‑force attacks that guess passwords. Social engineering tricks users into revealing confidential information.
网络安全保护数据和系统免受未经授权的访问、破坏或损害。主要威胁包括恶意软件（病毒、蠕虫、特洛伊木马）、网络钓鱼（索取个人信息的欺诈邮件）、用流量淹没服务器的拒绝服务攻击（DoS）以及猜测密码的暴力攻击。社会工程学诱骗用户泄露机密信息。
Prevention methods involve a layered approach. Firewalls monitor incoming and outgoing traffic and block unauthorised access based on predefined rules. Encryption scrambles data using algorithms like AES so that only authorised parties with the key can read it. Two‑factor authentication adds an extra verification step. Regular software updates patch known vulnerabilities, and user education reduces the risk of falling for phishing and social engineering. Strong password policies and access rights management further restrict exposure.
防范方法采用分层方式。防火墙监控进出流量，并根据预设规则阻止未经授权的访问。加密使用像 AES 这样的算法对数据进行加扰，只有持有密钥的授权方才能读取。双因素认证增加了一道额外的验证步骤。定期软件更新修补已知漏洞，而用户教育降低遭受网络钓鱼和社会工程攻击的风险。强密码策略和访问权限管理进一步限制风险暴露。
8. Software: System and Application | 软件：系统软件与应用软件
Software is divided into system software and application software. System software manages hardware and provides a platform for applications. The most important system software is the operating system (OS), which performs functions such as memory management, process scheduling, file management, provision of a user interface, peripheral management and security.
软件分为系统软件和应用软件。系统软件管理硬件并为应用程序提供平台。最重要的系统软件是操作系统（OS），它执行诸如内存管理、进程调度、文件管理、提供用户界面、外围设备管理和安全等功能。
Application software performs specific user‑oriented tasks, such as word processing, spreadsheets, web browsing and database management. Off‑the‑shelf software is ready‑made and cheaper, while bespoke software is custom‑built for specific needs. Also, programming language translators — compilers, interpreters and assemblers — are system software that converts source code into machine code. A compiler translates the entire program in one go; an interpreter translates line by line and executes immediately.
应用软件执行特定的面向用户的任务，例如文字处理、电子表格、网页浏览和数据库管理。现成的软件是预先制好的，价格较低，而定制的软件则是为特定需求专门构建的。此外，编程语言翻译器——编译器、解释器和汇编器——是将源代码转换成机器码的系统软件。编译器一次性翻译整个程序；解释器逐行翻译并立即执行。
9. Ethics and Legal Issues in Computing | 计算领域的伦理与法律问题
Computing technology raises significant ethical and legal questions. Plagiarism — using someone else’s work without permission or attribution — is a common issue in digital content. Copyright laws protect the intellectual property of creators, while software licences dictate how programs may be used, modified and distributed. Open‑source software grants users the freedom to study and change the code, whereas proprietary software restricts such access.
计算技术引发了重大的伦理和法律问题。剽窃——未经许可或未注明出处而使用他人的作品——是数字内容中的常见问题。版权法保护创作者的知识产权，而软件许可证规定了程序可以使用、修改和分发的方式。开源软件赋予用户学习和修改代码的自由，而专有软件则限制这种访问。
Data privacy is governed by regulations such as GDPR, which require organisations to obtain consent for data collection, store data securely and allow individuals to access their data. Ethical issues also include the digital divide, online surveillance, addiction to technology and the environmental impact of manufacturing and disposing of electronic devices. Students should be able to discuss these issues with reasoned arguments.
数据隐私受 GDPR 等法规的约束，这些法规要求组织在收集数据时获得同意、安全地存储数据并允许个人访问其数据。伦理问题还包括数字鸿沟、在线监控、对技术的成瘾以及制造和处置电子设备对环境的影响。学生应能够以合理的论据讨论这些问题。
10. Algorithms: Flowcharts, Pseudocode and Testing | 算法：流程图、伪代码与测试
An algorithm is a step‑by‑step procedure for solving a problem. In CAIE examinations, you will be expected to read, write and trace algorithms using either flowcharts or pseudocode. Flowcharts use standard symbols: oval for start/stop, parallelogram for input/output, rectangle for process, diamond for decision. Pseudocode uses structured English‑like syntax with keywords such as INPUT, OUTPUT, IF…THEN…ELSE…ENDIF, FOR…TO…NEXT, WHILE…DO…ENDWHILE.
算法是解决问题的逐步过程。在 CAIE 考试中，你需要使用流程图或伪代码来阅读、编写和追踪算法。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，菱形表示判断。伪代码使用结构化的类英语语法，包含诸如 INPUT、OUTPUT、IF…THEN…ELSE…ENDIF、FOR…TO…NEXT、WHILE…DO…ENDWHILE 等关键字。
Algorithm design involves sequence, selection (branching) and iteration (loops). Count‑controlled loops (FOR) execute a set number of times; condition‑controlled loops (WHILE, REPEAT…UNTIL) continue while a condition is true. Trace tables are essential for testing: they record the values of variables at each step to verify correctness. Additionally, understanding linear search versus binary search and bubble sort versus insertion sort is key for comparing efficiency. Binary search requires sorted data and is more efficient, with a time complexity naturally explained by halving the search space each iteration.
算法设计涉及顺序结构、选择结构（分支）和迭代结构（循环）。计数控制循环（FOR）执行固定次数；条件控制循环（WHILE、REPEAT…UNTIL）在条件为真时持续执行。追踪表对于测试至关重要：它们记录每一步中变量的值以验证正确性。此外，理解线性搜索与二分搜索以及冒泡排序与插入排序是比较效率的关键。二分搜索要求数据已排序，效率更高，其时间复杂度可以通过每次迭代将搜索空间减半来自然解释。
11. Databases: Structure and SQL | 数据库：结构与 SQL
A database is a structured collection of data. A flat‑file database stores data in a single table, which is simple but can lead to redundancy and inconsistency. A relational database organises data into linked tables using primary keys and foreign keys, reducing duplication and maintaining data integrity. Each table consists of records (rows) and fields (columns), with each field having a defined data type (text, number, date, Boolean, etc.).
数据库是结构化的数据集合。平面文件数据库将数据存储在单个表中，结构简单但可能导致冗余和不一致。关系型数据库使用主键和外键将数据组织成相互链接的表，从而减少重复并保持数据完整性。每个表由记录（行）和字段（列）组成，每个字段具有定义的数据类型（文本、数字、日期、布尔值等）。
ld2 FROM TableName WHERE condition ORDER BY field ASC/DESC; INSERT INTO TableName VALUES (… alue WHERE condition; DELETE FROM TableName WHERE condition. Understanding wildcards (LIKE '_pattern%') and the use of logical operators (AND, OR, NOT) is also required.
结构化查询语言（SQL）用于管理关系数据库。你必须能够编写基本的 SQL 语句： ld2 FROM TableName WHERE condition ORDER BY field ASC/DESC; INSERT INTO TableName VALUES (… UPDATE TableName SET field = value WHERE condition; DELETE FROM TableName WHERE condition。还需要理解通配符（LIKE '_pattern%'）以及逻辑运算符（AND、OR、NOT）的使用。
12. Examination Tips and Common Pitfalls | 考试技巧与常见误区
When answering theory questions, always use precise technical vocabulary. For example, say 'data is transferred using parallel transmission' rather than 'data moves quickly'. Show working for number conversions; a method mark can be awarded even if the final answer is wrong. In algorithm questions, draw a trace table even when not explicitly requested — it helps avoid logic errors. Pay close attention to units: file size questions often require conversions between bytes, kibibytes and mebibytes, and forgetting the difference between MB and MiB can cost marks.
在回答理论问题时，务必使用精确的技术词汇。例如，说“数据使用并行传输进行传输”，而不是“数据移动得很快”。进行数值转换时要展示计算步骤；即使最终答案错误，也可能获得方法分。在算法题中，即使没有明确要求也画出追踪表——这有助于避免逻辑错误。尤其要注意单位：文件大小问题常涉及字节、kibibyte 和 mebibyte 之间的转换，忘记 MB 与 MiB 的区别可能导致失分。
Common pitfalls include confusing RAM with ROM, mixing up lossy and lossless compression, failing to distinguish between a switch and a router, and writing SQL without a WHERE clause when updating or deleting. Revise the fetch‑decode‑execute cycle as a clear sequence of register transfers; many marks are lost by omitting the role of the program counter or the memory data register. Practice past paper questions under timed conditions and self‑mark using the mark schemes to understand exactly what examiners expect.
常见误区包括混淆 RAM 与 ROM、将有损和无损压缩搞混、分不清交换机与路由器，以及在编写 SQL 更新或删除语句时漏掉 WHERE 子句。将取指-译码-执行周期作为清晰的寄存器传输序列来复习；许多考生因漏掉程序计数器或内存数据寄存器的作用而失分。在计时条件下练习历年试卷真题，并使用评分方案自行批改，以准确了解考官的期望。
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