📚 GCSE Edexcel Computer Science Last-Minute Revision Notes | GCSE Edexcel 计算机：考前冲刺笔记
This revision guide condenses the most essential GCSE Edexcel Computer Science topics into concise, exam-focused notes. Every point is presented in clear English and Chinese to help you memorise key facts quickly before the exam.
这本复习指南将GCSE Edexcel计算机科学最核心的考点浓缩为简洁的冲刺笔记。每个知识点都以清晰的中英双语呈现，帮助你在考前快速记忆关键内容。
1. Computational Thinking & Algorithms | 计算思维与算法
Computational thinking involves decomposition, pattern recognition, abstraction, and algorithm design.
计算思维包括分解、模式识别、抽象和算法设计。
Decomposition breaks a complex problem into smaller, manageable parts.
分解是将复杂问题拆分成更小、更易管理的部分。
Abstraction focuses on essential information while ignoring irrelevant details.
抽象只关注必要信息，忽略无关细节。
An algorithm is a step-by-step sequence to solve a problem, represented using pseudocode or flowcharts.
算法是解决问题的逐步步骤，可以用伪代码或流程图表示。
Linear search checks each element in order until a match is found; binary search works on sorted data by repeatedly dividing the search interval in half.
线性搜索按顺序检查每个元素直到找到匹配项；二分搜索要求在有序数据上反复将搜索区间减半。
Bubble sort repeatedly steps through the list, swapping adjacent elements if they are in the wrong order. Merge sort divides the list into halves, recursively sorts them and merges the sorted halves.
冒泡排序反复遍历列表，如果相邻元素顺序错误就交换。归并排序将列表分成两半，递归排序后再合并已排序的两半。
2. Data Representation: Numbers & Text | 数据表示：数字与文本
Denary (base-10) uses digits 0-9. Binary (base-2) uses 0 and 1. Hexadecimal (base-16) uses 0-9 and A-F, often used to represent large binary numbers compactly.
十进制（基数10）使用数字0-9。二进制（基数2）使用0和1。十六进制（基数16）使用0-9和A-F，常用于紧凑地表示大二进制数。
To convert a denary integer to binary, repeatedly divide by 2 and record the remainders from bottom to top. For example, 13 in denary is 1101 in binary.
十进制整数转二进制：反复除以2，从下到上记录余数。例如，十进制13的二进制为1101。
Binary to denary: multiply each bit by its place value (powers of 2) and sum them. 1011₂ = 1×8 + 0×4 + 1×2 + 1×1 = 11.
二进制转十进制：将每个位乘以对应的位权（2的幂）然后求和。1011₂ = 1×8 + 0×4 + 1×2 + 1×1 = 11。
Hexadecimal to binary: each hex digit corresponds to a 4-bit nibble. A = 1010, F = 1111, so 3A₁₆ = 0011 1010₂.
十六进制转二进制：每个十六进制数字对应一个4位二进制组。A＝1010，F＝1111，所以3A₁₆ = 0011 1010₂。
Characters are encoded using standards: ASCII uses 7 or 8 bits, covering English letters and symbols. Unicode extends this to support many languages and emojis, using up to 32 bits per character.
字符使用标准编码：ASCII用7或8位，涵盖英文字母和符号。Unicode扩展了字符集，支持多种语言和表情符号，每个字符最多使用32位。
3. Binary Arithmetic & Logic Shifts | 二进制算术与逻辑移位
Binary addition follows these rules: 0+0=0, 0+1=1, 1+0=1, 1+1=0 with a carry of 1 to the next column. Overflow occurs when the result exceeds the available bits (e.g., 8-bit sum > 11111111₂).
二进制加法规则：0+0=0，0+1=1，1+0=1，1+1=0 并向下一列进1。当结果超出可用位数时发生溢出（如8位求和＞11111111₂）。
Arithmetic left shift multiplies a binary number by 2 for each shift position. For example, shifting 00001101 (13) left by 2 yields 00110100 (52), i.e., 13 × 2² = 52.
算术左移每移一位相当于乘2。例如，将00001101（13）左移2位得到00110100（52），即13 × 2² = 52。
Arithmetic right shift divides by 2, preserving the sign bit (MSB) for negative numbers when using two’s complement. Logical right shift simply fills with zeros.
算术右移除以2，在使用补码表示负数时保留符号位（最高有效位）。逻辑右移直接填充0。
An overflow flag in the CPU is set when a calculation result does not fit in the destination register. It can cause errors in programs if not handled.
当计算结果无法放入目标寄存器时，CPU的溢出标志位会被置位。如不处理，可能导致程序错误。
4. Images, Sound & Compression | 图像、声音与压缩
Bitmap images are made of pixels. Colour depth (bits per pixel) determines the number of colours. For example, 8-bit colour depth provides 2⁸ = 256 colours. Resolution is the number of pixels e.g., 1920×1080.
位图图像由像素组成。颜色深度（每像素位数）决定颜色数量。例如8位色深提供2⁸＝256种颜色。分辨率是指像素数量，如1920×1080。
Image file size (in bits) = width × height × colour depth. Metadata (e.g., file format, date) also adds to file size.
图像文件大小（位）= 宽度 × 高度 × 颜色深度。元数据（如文件格式、日期）也会增加文件大小。
Sound is digitised by sampling. Sample rate (Hz) is the number of samples per second. Sample resolution (bits) determines the number of amplitude levels. Higher rates and bits give better quality but larger files.
声音通过采样数字化。采样率（Hz）是每秒采样次数。采样分辨率（位）决定振幅级数。更高的采样率和位深度音质更好，但文件更大。
Sound file size (bits) = sample rate × sample resolution × duration (seconds) × number of channels.
声音文件大小（位）= 采样率 × 采样分辨率 × 持续时间（秒） × 声道数。
Lossless compression (e.g., run-length encoding, Huffman coding) reduces file size without losing any data. Lossy compression (e.g., JPEG, MP3) removes non-essential data permanently to achieve smaller sizes.
无损压缩（如行程编码、霍夫曼编码）在不丢失数据的情况下减小文件大小。有损压缩（如JPEG、MP3）永久去除非必要数据以获得更小文件。
5. CPU & System Architecture | CPU与系统架构
The CPU (Central Processing Unit) follows the Von Neumann architecture: Control Unit (CU) manages execution, Arithmetic Logic Unit (ALU) performs calculations, registers store temporary data, and the system bus transfers data and instructions.
CPU（中央处理器）遵循冯·诺依曼架构：控制单元（CU）管理执行，算术逻辑单元（ALU）进行计算，寄存器存储临时数据，系统总线传输数据和指令。
Key registers: Program Counter (PC) holds the address of the next instruction; Memory Address Register (MAR) holds the address of memory location being accessed; Memory Data Register (MDR) holds the data; Accumulator (ACC) stores results of ALU operations.
关键寄存器：程序计数器（PC）存放下一条指令地址；内存地址寄存器（MAR）存放正在访问的内存地址；内存数据寄存器（MDR）存放数据；累加器（ACC）存储ALU运算结果。
The Fetch-Decode-Execute cycle: CU fetches instruction from memory (PC → MAR → MDR → CIR), decodes it, and executes it (often using ALU). Then PC increments.
取指-译码-执行周期：CU从内存取指令（PC→MAR→MDR→CIR），译码，然后执行（通常使用ALU）。之后PC递增。
CPU performance is affected by clock speed (GHz), number of cores, and cache size. More cores allow parallel processing; larger cache reduces average memory access time.
CPU性能受时钟速度（GHz）、核心数和缓存大小影响。核心数越多可并行处理；更大缓存可减少平均内存访问时间。
Embedded systems are dedicated computers within larger devices (e.g., washing machines, cars). They are low-power, real-time, and have limited user interfaces.
嵌入式系统是内置于大型设备中的专用计算机（如洗衣机、汽车）。它们低功耗、实时性强，用户界面有限。
6. Memory & Storage | 内存与存储
Primary memory: RAM (Random Access Memory) is volatile, fast, and holds data and programs currently in use. ROM (Read-Only Memory) is non-volatile and stores the boot program (BIOS/firmware).
主存储器：RAM（随机存取存储器）易失、速度快，存放正在使用的数据和程序。ROM（只读存储器）非易失，存储引导程序（BIOS/固件）。
Secondary storage: magnetic (HDD) uses spinning platters; optical (CD, DVD, Blu-ray) uses lasers; solid-state (SSD, USB flash drives) uses NAND flash memory. SSDs are faster, more durable, and consume less power than HDDs but are more expensive per GB.
辅助存储：磁存储（HDD）使用旋转磁盘；光存储（CD、DVD、蓝光）使用激光；固态存储（SSD、USB闪存）使用NAND闪存。SSD比HDD更快、更耐用、功耗更低，但每GB成本更高。
Storage capacity units: byte, kilobyte (KB ~10³), megabyte (MB ~10⁶), gigabyte (GB ~10⁹), terabyte (TB ~10¹²). For memory, 1 KiB = 2¹⁰ bytes, but often approximated.
存储容量单位：字节、千字节（KB~10³）、兆字节（MB~10⁶）、吉字节（GB~10⁹）、太字节（TB~10¹²）。内存中1 KiB = 2¹⁰字节，但常作近似。
Virtual memory uses a portion of the hard disk as an extension of RAM. When RAM is full, inactive pages are moved to disk, allowing more programs to run but slowing performance due to disk thrashing.
虚拟内存使用硬盘的一部分作为内存扩展。当RAM满时，非活跃页面被移至磁盘，允许运行更多程序，但因磁盘频繁读写导致性能下降。
Cloud storage means storing data on remote servers accessed via the Internet. Advantages: accessibility anywhere, automatic backup, scalability. Disadvantages: requires Internet connection, ongoing subscription costs, security concerns.
云存储是将数据存储在可通过互联网访问的远程服务器上。优点：可在任何地方访问、自动备份、可扩展。缺点：需要网络连接、持续订阅费用、安全性问题。
7. Networks, Protocols & Topologies | 网络、协议与拓扑
LAN (Local Area Network) covers a small geographical area, usually one building. WAN (Wide Area Network) spans large distances, connecting LANs across cities/countries. The Internet is the largest WAN.
LAN（局域网）覆盖小范围区域，通常是一栋建筑。WAN（广域网）横跨长距离，连接不同城市/国家的LAN。互联网是最大的WAN。
Network topologies: star (all nodes connect to a central switch; easy to isolate faults, but switch failure affects the whole network), bus (single cable with terminators; cheap but collisions possible, failure breaks network), mesh (nodes interconnected, robust but expensive).
网络拓扑：星型（所有节点连到中央交换机；易于隔离故障，但交换机故障影响全网），总线型（单根电缆搭配终端器；便宜但可能冲突，一处断则全网断），网状（节点互连，健壮但昂贵）。
Protocols: TCP/IP (Transmission Control Protocol/Internet Protocol) is the foundation of the internet – TCP ensures reliable, ordered delivery; IP handles addressing and routing. HTTP/HTTPS (web), FTP (file transfer), SMTP (send email), POP3/IMAP (receive email).
协议：TCP/IP（传输控制协议/网际协议）是互联网的基础——TCP确保可靠有序传输；IP处理寻址和路由。HTTP/HTTPS（网页）、FTP（文件传输）、SMTP（发送邮件）、POP3/IMAP（接收邮件）。
The TCP/IP stack has 4 layers: Application, Transport, Internet, and Network Access. Each layer adds headers and passes data down; the reverse process occurs at the destination.
TCP/IP协议栈分4层：应用层、传输层、互联网层和网络接入层。每层添加头部并向下传递；在目的地进行反向过程。
Packet switching: data is split into packets, each containing source/destination IP, sequence number, and payload. Packets may take different routes and are reassembled at destination.
分组交换：数据分割成数据包，每个包含源/目的IP、序号和载荷。数据包可能走不同路由，在目的地重新组装。
8. Cybersecurity | 网络安全
Malware (malicious software) includes viruses (attach to files, spread), worms (self-replicate over networks), trojans (disguise as legitimate software), ransomware (locks data for ransom) and spyware (monitors user activity).
恶意软件包括病毒（附着文件传播）、蠕虫（在网络上自我复制）、特洛伊木马（伪装成合法软件）、勒索软件（锁定数据索要赎金）和间谍软件（监控用户活动）。
Social engineering tricks users into giving away confidential information. Phishing emails imitate trusted sources; blagging (pretexting) invents a scenario; shoulder surfing watches someone type passwords.
社会工程学诱骗用户泄露机密信息。网络钓鱼邮件模仿可信任来源；伪造身份（托辞）编造场景；肩窥则偷看他人输入密码。
Brute-force attacks try every possible password combination. Denial of Service (DoS) floods a server with traffic to make it unavailable. SQL injection inserts malicious SQL code into input fields to access or corrupt a database.
蛮力攻击尝试每种可能的密码组合。拒绝服务攻击（DoS）用流量淹没服务器使其不可用。SQL注入将恶意SQL代码插入输入字段以访问或破坏数据库。
Prevention: firewalls filter incoming/outgoing network traffic based on rules. Encryption scrambles data (e.g., AES, HTTPS). Penetration testing identifies vulnerabilities. Strong password policies, multi-factor authentication and regular updates reduce risk.
预防措施：防火墙按规则过滤网络流量。加密技术打乱数据（如AES、HTTPS）。渗透测试识别漏洞。强密码策略、多因素认证和定期更新可降低风险。
9. System Software & Utilities | 系统软件与实用工具
Operating system (OS) manages hardware and software resources, provides user interface (GUI/CLI), handles memory management, multitasking, and peripheral device drivers.
操作系统（OS）管理硬件和软件资源，提供用户界面（图形界面/命令行界面），处理内存管理、多任务和外围设备驱动程序。
The OS uses scheduling to allocate CPU time to processes (e.g., round-robin, priority-based). Interrupts are signals from hardware or software that cause the CPU to pause its current task and run an interrupt service routine.
操作系统通过调度分配CPU时间（如轮转法、优先级调度）。中断是硬件或软件发送的信号，让CPU暂停当前任务并执行中断服务程序。
Utility software performs specific tasks: defragmentation reorganizes fragmented files on HDDs to improve access speed; compression tools reduce file sizes; encryption utilities protect data; backup software creates copies of data.
实用工具软件执行特定任务：碎片整理重组HDD上的文件碎片以提高访问速度；压缩工具减小文件体积；加密工具保护数据；备份软件创建数据副本。
Open source software has source code freely available for modification and redistribution. Proprietary software is closed-source, usually requires paid licenses. Open source benefits include customisability and community support but may lack official support.
开源软件的源代码可自由获取、修改和重新分发。专有软件为闭源，通常需要付费许可。开源的好处包括可定制性和社区支持，但可能缺乏官方支持。
10. Programming Concepts | 编程概念
Basic data types: integer (whole numbers), float/real (decimals), Boolean (true/false), character (single symbol), string (sequence of characters). Variables are named storage locations; constants hold values that do not change.
基本数据类型：整数（整数）、浮点数/实数（小数）、布尔型（真/假）、字符（单个符号）、字符串（字符序列）。变量是命名的存储位置；常量保存不可变更的值。
Arithmetic operators: +, -, *, /, MOD (remainder), DIV (integer division). Comparison operators: ==, !=, >, <, >=, <=. Logical operators: AND, OR, NOT.
算术运算符：+、-、*、/、MOD（取余）、DIV（整除）。比较运算符：==、!=、>、<、>=、<=。逻辑运算符：AND、OR、NOT。
Sequence, selection, iteration: Sequence executes lines one after another. Selection (if-else, switch-case) executes code blocks based on conditions. Iteration includes for loops (count-controlled) and while/do-until loops (condition-controlled).
顺序、选择、迭代：顺序逐行执行。选择（if-else、switch-case）根据条件执行代码块。迭代包括for循环（计数控制）和while/do-until循环（条件控制）。
A trace table is used to track the values of variables as each line of an algorithm is executed. It helps detect logic errors. You manually step through the program, updating a table with variable changes after each statement.
跟踪表用于追踪算法每行执行后变量的值，帮助发现逻辑错误。你手动逐步执行程序，在每条语句后更新变量值的表格。
Subprograms: procedures (perform actions but do not return a value) and functions (return a value). Using parameters (by value or by reference) enables code reuse and modular design.
子程序：过程（执行操作但不返回值）和函数（返回一个值）。使用参数（传值或传引用）可实现代码重用和模块化设计。
11. Boolean Logic & Truth Tables | 布尔逻辑与真值表
Logic gates: NOT (output opposite of input), AND (output 1 only if both inputs are 1), OR (output 1 if at least one input is 1). XOR (exclusive OR) outputs 1 if inputs are different.
逻辑门：NOT（输出与输入相反）、AND（只有两输入均为1时输出1）、OR（至少一个输入为1时输出1）。XOR（异或）输入不同时输出1。
Truth tables show all possible input combinations and the corresponding output. For a 2-input AND gate, the output column is 0,0,0,1 for inputs 00,01,10,11.
真值表列出所有可能的输入组合及对应输出。对于2输入AND门，输入00,01,10,11时输出列为0,0,0,1。
Boolean expressions use notation such as A AND B (A∧B), A OR B (A∨B), NOT A (¬A). You can simplify expressions using Boolean laws (e.g., A∧(B∨C) = (A∧B)∨(A∧C)).
布尔表达式使用符号如A AND B (A∧B)，A OR B (A∨B)，NOT A (¬A)。可用布尔定律简化表达式（如分配律等）。
Creating a logic circuit from a truth table: for each row where output is 1, write the corresponding minterm (AND the inputs or their negations), then OR all minterms together to get the sum-of-products expression.
从真值表创建逻辑电路：对于每个输出为1的行，写出相应的最小项（将输入或其反进行与运算），然后将所有最小项进行或运算得到积之和表达式。
12. Ethical, Legal & Environmental Impacts | 道德、法律与环境影响
The Data Protection Act (2018) and GDPR regulate the collection, storage and use of personal data. Organisations must have consent, keep data secure, and allow individuals to access their data.
《数据保护法》（2018年）和GDPR规范个人数据的收集、存储和使用。组织须获得同意、保护数据安全，并允许个人访问其数据。
Computer Misuse Act (1990) makes unauthorised access to computer material, unauthorised access with intent to commit crime, and unauthorised modification of data illegal. Hacking and malware spreading fall under this act.
《计算机滥用法》（1990年）将未经授权访问计算机资料、意图犯罪而未经授权访问以及未经授权修改数据定为非法。黑客攻击和传播恶意软件受此法管辖。
Copyright, Designs and Patents Act protects intellectual property, making it illegal to copy, download or distribute software, music, films without permission. Plagiarism is using someone else’s work without credit.
《版权、设计和专利法》保护知识产权，未经许可复制、下载或分发软件、音乐、电影属于非法。剽窃是指使用他人作品而不注明出处。
The digital divide refers to the gap between those who have access to modern digital technology and those who do not, affected by factors such as income, location, and education.
数字鸿沟指能接触到现代数字技术的人与无法接触的人之间的差距，受收入、地理位置和教育等因素影响。
Environmental issues: manufacturing computers uses energy and rare materials, and e-waste contains toxic substances. Data centres consume large amounts of electricity, contributing to carbon emissions. Recycling and energy-efficient design help mitigate these impacts.
环境问题：制造计算机消耗能源和稀有材料，电子垃圾含有有毒物质。数据中心消耗大量电力，增加碳排放。回收和节能设计有助于减轻这些影响。
Published by TutorHao | Computer Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导