📚 Core Knowledge Review for Year 11 CIE Computer Science | Year 11 CIE 计算机：核心知识点梳理
This article distils the essential topics you need to master for the CIE IGCSE Computer Science (0478/0984) examinations. We will cover data representation, hardware, software, networking, security, algorithms, programming, databases and ethical considerations. Use this as a revision map to reinforce your understanding and close any gaps before your final papers.
本文梳理了 CIE IGCSE 计算机科学 (0478/0984) 考试必须掌握的核心主题，涵盖数据表示、硬件、软件、网络、安全、算法、编程、数据库和伦理考量。请将本文作为复习地图，在最终考试前巩固理解、查漏补缺。
1. Data Representation | 数据表示
All data inside a computer is stored as binary digits (bits), with each bit representing a 0 or a 1. Numbers, text, sounds and images must be encoded into binary patterns before a computer can process them.
计算机内部的所有数据都以二进制数字（比特）存储，每个比特代表 0 或 1。数字、文本、声音和图像必须先编码为二进制模式，计算机才能处理。
11101. Binary addition follows the same column rules as denary, with 1+1 = 0 carry 1. Overflow occurs when the result exceeds the available number of bits, leading to inaccurate results.
将正整数转换为二进制，使用连续除以 2 并自下而上记录余数的方法。例如，29 的二进制表示为 11101。二进制加法遵循与十进制相同的列规则，1+1 = 0 进 1。当结果超出可用的比特数时会发生溢出，导致结果不准确。
Hexadecimal (base 16) uses digits 0–9 and letters A–F, providing a compact way to represent binary. One hex digit corresponds to four bits. Programmers use hex for memory addresses, colour codes and error messages. Converting between binary and hex is done by grouping bits into nibbles.
十六进制（基数为 16）使用数字 0–9 和字母 A–F，提供一种紧凑的二进制表示方式。一个十六进制数字对应四个比特。编程人员用十六进制表示内存地址、颜色代码和错误信息。二进制与十六进制间的转换通过将比特分组为半字节完成。
Text is represented using character sets. ASCII uses 7 bits per character (stored in a byte), encoding 128 characters. Extended ASCII uses 8 bits for 256 characters. Unicode, such as UTF-8, can represent characters from all global writing systems using variable-length encoding. Sound is captured by sampling the amplitude at regular intervals. The sampling rate (Hz) and bit depth determine the quality and file size: higher values yield truer reproduction but larger files.
文本使用字符集表示。ASCII 每个字符使用 7 比特（存储在一个字节），编码 128 个字符。扩展 ASCII 使用 8 比特编码 256 个字符。Unicode（如 UTF-8）可使用变长编码表示全球所有书写系统的字符。声音通过定期对振幅采样而捕获。采样率（赫兹）和比特深度决定声音质量和文件大小：数值越高，还原越真实，但文件也越大。
Images are represented as bitmaps, a grid of pixels. Each pixel is assigned a binary colour value. Resolution is the total number of pixels, while colour depth is the number of bits per pixel. More bits per pixel support more colours; for example, 8 bits give 256 colours per pixel. Vector graphics store drawing instructions instead of pixels, making them scalable without loss of quality.
图像表示为位图，即像素网格。每个像素分配一个二进制颜色值。分辨率是像素总数，而颜色深度是每个像素的比特数。每像素的比特数越多，支持的颜色越多；例如，8 比特给出 256 种颜色。矢量图形存储绘图指令而非像素，可无质量损失地缩放。
2. Computer Architecture | 计算机体系结构
The central processing unit (CPU) follows the Von Neumann architecture: it fetches instructions from memory, decodes them and then executes them. The three main components are the control unit (CU), the arithmetic logic unit (ALU) and registers.
中央处理器 (CPU) 遵循冯·诺依曼体系结构：它从内存中取指令、解码指令，然后执行指令。三个主要组件是控制单元 (CU)、算术逻辑单元 (ALU) 和寄存器。
Registers are extremely fast memory locations inside the CPU. The program counter (PC) holds the address of the next instruction; the memory address register (MAR) stores the address currently being accessed; the memory data register (MDR) holds the actual data or instruction; the current instruction register (CIR) contains the instruction being decoded; and the accumulator (ACC) temporarily stores results from the ALU.
寄存器是 CPU 内部极快的内存位置。程序计数器 (PC) 存放下一条指令的地址；内存地址寄存器 (MAR) 存储当前访问的地址；内存数据寄存器 (MDR) 保存实际数据或指令；当前指令寄存器 (CIR) 包含正在解码的指令；累加器 (ACC) 临时存储 ALU 的运算结果。
Factors affecting CPU performance include clock speed (GHz), number of cores and cache size. A higher clock speed means more cycles per second. More cores allow parallel processing of instructions. Cache memory is extremely fast RAM that stores frequently accessed data and instructions, reducing the need to fetch from slower main memory.
影响 CPU 性能的因素包括时钟速度 (GHz)、内核数量和缓存大小。时钟速度越高，每秒周期数越多。更多内核允许并行处理指令。高速缓存是极快的 RAM，存储频繁访问的数据和指令，减少从较慢主内存取指的需要。
The fetch–decode–execute cycle describes how the CPU processes instructions. In the fetch stage, the instruction at the PC address is copied to the MDR and the PC is incremented. In the decode stage, the CU interprets the instruction. During execute, the relevant operation is performed, often involving the ALU.
取指-解码-执行周期描述 CPU 如何处理指令。在取指阶段，PC 地址处的指令复制到 MDR，PC 递增。在解码阶段，CU 解释该指令。在执行阶段，执行相关操作，通常涉及 ALU。
3. Input and Output Devices | 输入与输出设备
Input devices convert real-world phenomena into digital data. A keyboard enters text mechanically; a microphone captures analogue sound and an analogue-to-digital converter samples it; a flatbed scanner uses a moving sensor bar to digitise documents. Sensors (temperature, light, pressure) continuously collect environmental data and often require an ADC.
输入设备将现实世界的现象转换为数字数据。键盘机械输入文本；麦克风捕获模拟声音并由模数转换器采样；平板扫描仪使用移动的传感器条扫描文档。传感器（温度、光线、压力）持续采集环境数据，通常需要模数转换器。
Output devices present processed data. Monitors (LCD/LED) use grids of pixels to display images; projectors enlarge the display onto a screen. Printers include inkjet printers, which spray fine droplets of ink, and laser printers, which use electrostatic charges and toner to produce high-speed, high-quality prints. Speakers and headphones reverse the sampling process by converting digital signals to analogue sound waves.
输出设备呈现已处理的数据。显示器 (LCD/LED) 使用像素网格显示图像；投影仪将显示放大投射到屏幕上。打印机包括喷墨打印机（喷射微小墨滴）和激光打印机（使用静电和碳粉高速、高质量打印）。扬声器和耳机将数字信号转换为模拟声波，逆转采样过程。
Touchscreens are both input and output devices. Capacitive touchscreens detect the electrical properties of the human finger, while resistive screens rely on physical pressure. Actuators and buzzers convert signals into motion or sound, often used in control systems.
触摸屏既是输入设备也是输出设备。电容式触摸屏检测人体手指的电特性，而电阻式屏幕依赖物理压力。执行器与蜂鸣器将信号转换为运动或声音，常用于控制系统。
4. Memory and Storage | 存储器与存储
Primary memory is directly addressable by the CPU. RAM (random access memory) is volatile, holds the operating system, applications and data currently in use, and loses its content when power is off. ROM (read only memory) is non-volatile, stores the boot-up program (BIOS/firmware) and cannot be easily modified.
主存储器可由 CPU 直接寻址。随机存取存储器 (RAM) 易失，保存当前使用的操作系统、应用程序和数据，断电后内容丢失。只读存储器 (ROM) 非易失，存储引导程序 (BIOS/固件)，不能轻易修改。
Secondary storage provides permanent, non-volatile storage. Magnetic storage (HDD) uses spinning platters and read/write heads; it offers high capacity at low cost but is susceptible to physical shock. Optical storage (CD, DVD, Blu-ray) uses lasers to read pits and lands; suitable for distributing media but has limited capacity. Solid-state storage (SSD, USB flash, SD cards) uses NAND flash memory, has no moving parts, faster read/write speeds and lower power consumption, but costs more per gigabyte.
辅助存储器提供永久的非易失存储。磁性存储 (HDD) 使用旋转盘片和读写头；容量高、成本低，但易受物理冲击影响。光存储 (CD、DVD、蓝光) 使用激光读取凹坑和平面；适合分发媒体，但容量有限。固态存储 (SSD、U 盘、SD 卡) 使用 NAND 闪存，无移动部件，读写速度快，功耗更低，但每 GB 成本更高。
5. Networking and the Internet | 网络与互联网
A network connects computers to share resources and communicate. LANs cover a small geographic area, usually using Ethernet or Wi-Fi. WANs cover large distances; the Internet is the largest WAN. Client-server networks rely on powerful servers to manage resources, while peer-to-peer networks allow devices to share equally without a central server.
网络连接计算机以共享资源和通信。局域网 (LAN) 覆盖较小地理区域，通常使用以太网或 Wi-Fi。广域网 (WAN) 覆盖长距离；互联网是最大的 WAN。客户-服务器网络依赖强大的服务器管理资源，而对等网络允许设备平等共享，无需中央服务器。
Data is broken into packets and transmitted using protocols. TCP/IP is the fundamental protocol suite: IP handles addressing and routing; TCP ensures reliable delivery. Each device requires a unique IP address. MAC addresses are hardware identifiers. Routers direct packets between networks, while switches connect devices within a LAN based on MAC addresses.
数据被拆分为数据包并利用协议传输。TCP/IP 是基础协议族：IP 负责寻址和路由；TCP 确保可靠传递。每台设备需要唯一的 IP 地址。MAC 地址是硬件标识符。路由器在网络间定向数据包，而交换机基于 MAC 地址连接局域网内的设备。
Common transmission media include copper (Ethernet cables, twisted pair), fibre optic (fast, immune to interference, uses light) and wireless (radio waves, Wi-Fi, Bluetooth). Network topologies such as star (all nodes connect to a central switch) and mesh (redundant links) affect reliability and cost.
常见传输介质包括铜缆（以太网线、双绞线）、光纤（快速、抗干扰、使用光）和无线（无线电波、Wi-Fi、蓝牙）。网络拓扑如星型（所有节点连接中央交换机）和网状（冗余链路）会影响可靠性和成本。
6. Network Security | 网络安全
Networks face threats such as malware (viruses, worms, Trojan horses), phishing, denial-of-service (DoS) attacks and brute-force password attacks. Malware can spread via email attachments, infected downloads or network vulnerabilities.
网络面临恶意软件（病毒、蠕虫、特洛伊木马）、网络钓鱼、拒绝服务 (DoS) 攻击和暴力密码攻击等威胁。恶意软件可通过电子邮件附件、受感染的下载或网络漏洞传播。
Encryption scrambles data using an algorithm and a key, so only someone with the correct key can decrypt it. Symmetric encryption uses the same key for both encryption and decryption; asymmetric encryption uses a public key to encrypt and a private key to decrypt, enabling secure communication without pre-sharing a secret key.
加密使用算法和密钥扰乱数据，只有拥有正确密钥的人才能解密。对称加密加密和解密使用相同密钥；非对称加密使用公钥加密、私钥解密，无需预先共享密钥即可实现安全通信。
Security measures include firewalls (filter incoming and outgoing traffic based on rules), anti-malware software, strong authentication (passwords, biometrics, two-factor), regular software updates and user education. A proxy server can hide a network’s IP addresses and cache web content.
安全措施包括防火墙（根据规则过滤进出流量）、反恶意软件、强身份验证（密码、生物识别、双因素）、定期软件更新和用户教育。代理服务器可隐藏网络 IP 地址并缓存网页内容。
7. Systems Software | 系统软件
Operating systems manage hardware resources, provide a user interface, handle file management, process management and peripheral communication. They enable multitasking by allocating processor time slices to each active process.
操作系统管理硬件资源、提供用户界面、处理文件管理、进程管理和外设通信。操作系统通过向每个活动进程分配处理时间片来支持多任务处理。
Utility software performs maintenance tasks: file compression reduces file size; defragmentation reorganises data on an HDD for faster access (not needed for SSDs); backup utilities create copies of data; and encryption utilities secure files.
实用软件执行维护任务：文件压缩减小文件体积；碎片整理重新组织 HDD 上的数据以加快访问（SSD 不需要）；备份实用程序创建数据副本；加密实用程序保护文件。
The operating system kernel remains in main memory, managing interrupts and system calls. Device drivers translate OS instructions into commands specific to a hardware device, ensuring the OS can work with diverse printers, graphics cards and keyboards.
操作系统内核驻留在主存中，管理中断和系统调用。设备驱动程序将操作系统指令转换为特定于硬件设备的命令，确保操作系统能与各式各样的打印机、显卡和键盘配合工作。
8. Ethics, Legal Issues and Environmental Impact | 伦理、法律与环境影响
Computer technologies raise ethical concerns about privacy, data misuse and the digital divide. Plagiarism, hacking and cyberbullying are unethical uses of computing. The digital divide refers to the gap between those who have access to technology and those who do not.
计算机技术引发了关于隐私、数据滥用和数字鸿沟的伦理关注。剽窃、黑客行为和网络欺凌是不道德的计算机使用。数字鸿沟指的是能获取技术的人群与不能获取技术的人群之间的差距。
Legal frameworks address these issues: the Data Protection Act governs how personal data can be collected, stored, and used, with principles such as data minimisation and accuracy. The Computer Misuse Act criminalises unauthorised access, unauthorised modification of data, and creating or distributing malware. The Copyright, Designs and Patents Act protects intellectual property including software and digital media.
法律框架处理这些问题：《数据保护法》规范了个人数据的收集、存储和使用，包含数据最小化和准确性等原则。《计算机滥用法》将未经授权的访问、未授权修改数据以及制作或传播恶意软件定为犯罪。《版权、设计和专利法》保护软件和数字媒体等知识产权。
The environmental impact of computing includes energy consumption by data centres, e-waste from discarded devices, and resource depletion from manufacturing. Green computing promotes energy-efficient hardware, virtualisation, proper e-waste recycling and laws like the WEEE Directive.
计算的环境影响包括数据中心的高能耗、废弃设备产生的电子垃圾以及制造过程中的资源枯竭。绿色计算提倡节能硬件、虚拟化、适当的电子垃圾回收以及 WEEE 指令等法律。
9. Algorithm Design and Problem Solving | 算法设计与问题解决
An algorithm is a step-by-step procedure to solve a problem. Algorithms can be expressed in pseudocode or flowcharts. Flowcharts use standard symbols: oval for start/end, parallelogram for input/output, rectangle for process, diamond for decision.
算法是解决问题的分步程序。算法可用伪代码或流程图表示。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。
Basic constructs are sequence, selection (IF…THEN…ELSE) and iteration (loops). FOR loops repeat a known number of times; WHILE loops continue as long as a condition is true; REPEAT…UNTIL loops execute at least once and stop when a condition becomes true. Nested statements allow complex logic.
基本结构有顺序、选择 (IF…THEN…ELSE) 和迭代（循环）。FOR 循环重复已知次数；WHILE 循环在条件为真时持续；REPEAT…UNTIL 循环至少执行一次，当条件为真时停止。嵌套语句实现复杂逻辑。
Searching and sorting algorithms are frequently tested. Linear search inspects every element until the target is found; it works on unsorted lists. Binary search halves the search space each time, requiring a sorted list. Bubble sort repeatedly steps through the list, swapping adjacent items if they are in the wrong order; insertion sort builds a sorted sublist by placing each item at its correct position.
搜索和排序算法常考。线性搜索检查每个元素直到找到目标，适用于无序列表。二分搜索每次将搜索范围减半，需要有序列表。冒泡排序重复遍历列表，在相邻项顺序错误时交换；插入排序通过将每个元素插入正确位置来构建有序子列表。
Pseudocode must use assignment (←), conditional statements (CASE OF, otherwise) and input/output (INPUT, OUTPUT). Trace tables help to dry-run algorithms and identify logical errors.
伪代码必须使用赋值 (←)、条件语句 (CASE OF, otherwise) 和输入输出 (INPUT, OUTPUT)。跟踪表用于手工运行算法并找出逻辑错误。
10. Programming Concepts | 编程概念
Variables are named memory locations that store values; constants are values that do not change during execution. Data types include integer, real/float, Boolean (TRUE/FALSE), char and string. String manipulation involves concatenation, length calculation and substring extraction.
变量是命名的存储位置，用于存储值；常量是执行期间不变的值。数据类型包括整型、实型/浮点型、布尔型 (TRUE/FALSE)、字符和字符串。字符串操作包括连接、长度计算和子串提取。
Arrays (lists) store multiple elements of the same data type under a single identifier. Index positions usually start at 0 or 1. Two-dimensional arrays resemble a grid. For example, array[2,3] refers to row 2, column 3. Reading and writing array elements is essential for iterative processing.
数组（列表）在单一标识符下存储多个同类型元素。索引位置通常从 0 或 1 开始。二维数组类似网格。例如，array[2,3] 指向第 2 行第 3 列。迭代处理离不开数组元素的读写。
Procedures and functions group reusable blocks of code. A procedure performs a task; a function performs a task and returns a value. Parameters can be passed by value (copied) or by reference (original variable is accessible). Local and global variables have different scopes.
过程和函数将可重用代码块组织在一起。过程执行任务；函数执行任务并返回一个值。参数可以按值传递（复制）或按引用传递（可访问原变量）。局部变量和全局变量具有不同的作用域。
11. Databases and SQL | 数据库与 SQL
A database is a structured collection of data. Relational databases store data in tables (relations) made up of records (rows) and fields (columns). Each table has a primary key that uniquely identifies each record. Foreign keys link tables together.
数据库是结构化的数据集合。关系数据库将数据存储在由记录（行）和字段（列）构成的表（关系）中。每个表有一个主键，唯一标识每条记录。外键将表关联起来。
SQL (Structured Query Language) is used to manage databases. The SELECT statement retrieves fields: SELECT field1, field2 FROM table WHERE condition ORDER BY field ASC/DESC;. The WHERE clause filters records using comparison operators and logical operators (AND, OR, NOT). The wildcard * selects all fields.
SQL（结构化查询语言）用于管理数据库。SELECT 语句检索字段：SELECT field1, field2 FROM table WHERE condition ORDER BY field ASC/DESC;。WHERE 子句使用比较运算符和逻辑运算符 (AND, OR, NOT) 筛选记录。通配符 * 选取所有字段。
Other data handling includes INSERT INTO to add records, UPDATE…SET to modify records and DELETE to remove records. Ensuring data integrity involves validation (checking data format) and verification (ensuring data matches the source).
其他数据处理包括 INSERT INTO 添加记录、UPDATE…SET 修改记录和 DELETE 删除记录。确保数据完整性涉及验证（检查数据格式）和核实（确保数据与来源一致）。
12. Logic Gates and Circuits | 逻辑门与逻辑电路
Logic gates are the building blocks of digital circuits. Each gate performs a Boolean function on binary inputs. The basic gates are NOT (output is opposite of input), AND (outputs 1 only if all inputs are 1), and OR (outputs 1 if any input is 1).
逻辑门是数字电路的基础构件。每个门对二进制输入执行布尔函数。基本门包括非门（输出与输入相反）、与门（仅当所有输入为 1 时输出 1）和或门（只要任一输入为 1 则输出 1）。
ble input combinations and the corresponding outputs. For example, an AND gate truth table: 0·0=0, 0·1=0, 1·0=0, 1·1=1.
复合门包括与非门 (NOT AND)、或非门 (NOT OR) 和异或门（当输入不同时输出 1）同样重要。真值表列出了所有可能的输入组合及其对应的输出。例如，与门真值表：0·0=0，0·1=0，1·0=0，1·1=1。
Logic circuits are represented using standard symbols. You must be able to draw a circuit from a Boolean expression and vice versa. Commutative, associative and distributive laws can be used to simplify expressions, but the IGCSE examination focuses on understanding circuits and constructing truth tables.
逻辑电路使用标准符号表示。你必须能够根据布尔表达式绘制电路，反之亦然。交换律、结合律和分配律可用于化简表达式，但 IGCSE 考试侧重于理解电路和构造真值表。
A logic diagram can be evaluated by writing the intermediate outputs at each gate until the final output is obtained. This links directly to problem-solving scenarios such as designing simple control systems with sensors and actuators.
逻辑图可通过写出每个门的中间输出直到最终输出求出来进行评估。这直接联系到问题解决场景，如用传感器和执行器设计简单控制系统。
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