📚 GCSE OCR Computer Science: Mind Map Quick Revision | GCSE OCR 计算机：思维导图速记
Mind maps help you visualise the connections between key concepts in GCSE OCR Computer Science. This quick revision guide breaks down each topic into bite-sized, paired English-Chinese summaries for easy memorisation.
思维导图帮助你直观理解GCSE OCR计算机科学中关键概念之间的联系。这份速记指南将每个主题分解为精炼的中英对照要点，便于记忆。
1. Systems Architecture | 系统架构
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The Von Neumann architecture stores both data and instructions in the same memory; it uses a single shared bus system between CPU and memory.
冯·诺依曼架构将数据和指令存放在同一内存中；它使用 CPU 与内存之间的单一共享总线系统。
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The CPU consists of the Control Unit (CU) that decodes instructions, the Arithmetic Logic Unit (ALU) that performs calculations, and registers that hold temporary data.
CPU 由负责译码的控制单元 (CU)、执行运算的算术逻辑单元 (ALU) 以及暂存数据的寄存器组成。
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Key registers: Program Counter (PC) holds the address of the next instruction; Memory Address Register (MAR) holds the address to be read/written; Memory Data Register (MDR) holds the data transferred; Accumulator (ACC) holds 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) 存放要读写的地址；内存数据寄存器 (MDR) 存放传输的数据；累加器 (ACC) 存放 ALU 运算结果。
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The fetch-decode-execute cycle: 1) Fetch instruction from the address in PC to MDR, PC incremented; 2) CU decodes the instruction; 3) Execute — ALU performs the operation and stores result in ACC or memory.
取指-译码-执行周期：1) 根据 PC 中的地址将指令取到 MDR，PC 递增；2) CU 译码指令；3) 执行 — ALU 完成操作并将结果存入 ACC 或内存。
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CPU performance is affected by clock speed (cycles per second, measured in GHz), number of cores (parallel task handling), and cache memory (small, fast memory near CPU for frequently used instructions).
CPU 性能受时钟速度（以 GHz 为单位）、核心数量（并行处理任务）和高速缓存（靠近 CPU 的小容量快速内存，存放常用指令）的影响。
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Embedded systems are dedicated microprocessors within larger devices (e.g., washing machines, microwaves); they are low-power, have limited user interfaces, and perform a single function repeatedly.
嵌入式系统是大型设备内部专用的微处理器（如洗衣机、微波炉）；它们功耗低，用户界面有限，重复执行单一功能。
2. Memory & Storage | 内存与存储
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Primary storage: RAM is volatile (loses data without power) and holds currently running programs and data; ROM is non-volatile and stores firmware/BIOS instructions needed to boot the computer.
主存：RAM 易失（断电丢失数据），存放正在运行的程序和数据；ROM 非易失，存储启动计算机所需的固件/BIOS 指令。
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Virtual memory uses a portion of secondary storage as if it were RAM when main RAM is full; it is much slower than physical RAM and can cause performance degradation.
虚拟内存在主内存不足时，将一部分辅助存储器当作 RAM 使用；它比物理 RAM 慢很多，可能导致性能下降。
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Secondary storage types: magnetic hard disks (HDD) offer large capacity at low cost but are mechanical and slower; solid-state drives (SSD) are fast, durable, and have no moving parts but cost more per GB; optical discs (CD, DVD, Blu-ray) are portable but limited in capacity.
辅助存储类型：磁性硬盘 (HDD) 容量大、成本低，但机械式且较慢；固态硬盘 (SSD) 速度快、耐用、无活动部件，但每 GB 成本更高；光盘 (CD, DVD, 蓝光) 便携但容量有限。
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When choosing storage, consider capacity, read/write speed, portability, durability, cost, and reliability.
选择存储设备时需考虑容量、读写速度、便携性、耐用性、成本以及可靠性。
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Data units (ascending): 1 bit → 4 bits = 1 nibble → 8 bits = 1 byte → 1,000 bytes ≈ 1 kilobyte (KB) → 1,000 KB ≈ 1 megabyte (MB) → 1,000 MB ≈ 1 gigabyte (GB) → 1,000 GB ≈ 1 terabyte (TB).
数据单位（由小到大）：1 bit → 4 bits = 1 半字节 → 8 bits = 1 字节 → 1,000 字节 ≈ 1 KB → 1,000 KB ≈ 1 MB → 1,000 MB ≈ 1 GB → 1,000 GB ≈ 1 TB。
3. Data Representation | 数据表示
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Binary arithmetic: shifting a binary number left multiplies it by 2 for each place; shifting right divides by 2 (integer division). Overflow occurs when a result exceeds the allocated number of bits.
二进制运算：左移一位相当于乘以 2；右移一位相当于除以 2（整数除法）。当结果超出分配的位数时发生溢出。
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Hexadecimal (base-16) uses 0-9 and A-F; each hex digit represents exactly 4 bits, making it shorthand for binary. Used for MAC addresses and colour codes (#RRGGBB).
十六进制 (基数为 16) 使用 0-9 和 A-F；每个十六进制位恰好表示 4 个二进制位，是二进制的一种简写，用于 MAC 地址和颜色编码 (#RRGGBB)。
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Character sets: ASCII uses 7 bits (128 characters) and Extended ASCII uses 8 bits (256 characters). Unicode supports a vast range of characters using up to 32 bits per character, enabling worldwide language representation.
字符集：ASCII 使用 7 位 (128 个字符)，扩展 ASCII 使用 8 位 (256 个字符)。Unicode 支持海量字符，每个字符最多使用 32 位，可实现全球语言表示。
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Images are represented as bitmaps composed of pixels. Colour depth (bits per pixel) determines the number of available colours; resolution (width × height) determines the number of pixels. File size (bits) = width × height × colour depth.
图像以位图表示，由像素组成。颜色深度（每像素位数）决定了可用颜色数量；分辨率（宽 × 高）决定了像素总数。文件大小 (bits) = 宽 × 高 × 颜色深度。
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Sound is digitised by sampling the analogue signal at regular intervals (sample rate in Hz) and storing the amplitude as a binary number (bit depth). File size (bits) = sample rate × bit depth × duration (seconds) for mono. Stereo doubles the calculation.
声音数字化通过以固定间隔对模拟信号采样（采样率，单位 Hz）并将振幅存储为二进制数（位深度）实现。文件大小 (bits) = 采样率 × 位深度 × 时长 (秒)，单声道。立体声需加倍计算。
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Compression: lossy (e.g., MP3, JPEG) permanently removes some data to drastically reduce file size, quality may degrade. Lossless (e.g., PNG, ZIP) reduces file size by removing redundancy but allows exact original data reconstruction.
压缩：有损 (如 MP3, JPEG) 永久性移除部分数据以大幅减小文件大小，质量可能下降。无损 (如 PNG, ZIP) 通过消除冗余来减小文件大小，但可以精确重建原始数据。
4. Boolean Logic | 布尔逻辑
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Logic gates process one or more binary inputs to produce a single binary output. AND outputs 1 only if all inputs are 1; OR outputs 1 if at least one input is 1; NOT inverts the input (output opposite).
逻辑门处理一个或多个二进制输入，产生单个二进制输出。AND 仅在所有输入为 1 时输出 1；OR 在至少一个输入为 1 时输出 1；NOT 反转输入（输出相反）。
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Combined gates: NAND is AND followed by NOT (output false only when all inputs true); NOR is OR followed by NOT; XOR outputs true when inputs differ.
组合门：NAND 是 AND 后接 NOT（仅在所有输入为真时输出假）；NOR 是 OR 后接 NOT；XOR 在输入不同时输出真。
AND gate truth table:
| Input A | Input B | Output Q |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
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A logic circuit diagram can be represented using a Boolean expression. For example, Q = (A AND B) OR (NOT C). From the expression we can create a truth table by evaluating all input combinations.
逻辑电路图可以用布尔表达式表示。例如，Q = (A AND B) OR (NOT C)。根据表达式可通过计算所有输入组合来创建真值表。
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Simple Boolean laws help simplify circuits: identity (A+0=A, A·1=A), annulment (A+1=1, A·0=0), complement (A+¬A=1, A·¬A=0).
简单的布尔定律有助于简化电路：同一律 (A+0=A, A·1=A)、归零律 (A+1=1, A·0=0)、互补律 (A+¬A=1, A·¬A=0)。
5. Computer Networks | 计算机网络
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LAN (Local Area Network) covers a small geographical area, often owned by an organisation and using switches and cables. WAN (Wide Area Network) connects LANs over vast distances, typically using leased telecommunication lines.
LAN（局域网）覆盖较小地理区域，通常由某个组织拥有并使用交换机和网线。WAN（广域网）通过远距离连接多个 LAN，通常使用租用通信线路。
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Factors affecting network performance: bandwidth (maximum data transfer capacity), number of users (contention ratio), transmission media (fibre optic > copper > wireless), and error rate causing re-transmissions.
影响网络性能的因素：带宽（最大数据传输能力）、用户数量（争用比）、传输介质（光纤 > 铜缆 > 无线）以及导致重传的错误率。
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Network hardware: Network Interface Card (NIC) connects a device to a network; switch sends data frames to the correct device in a LAN using MAC addresses; router forwards packets between different networks using IP addresses; Wireless Access Point (WAP) enables Wi-Fi connections.
网络硬件：网卡 (NIC) 将设备连接至网络；交换机根据 MAC 地址在 LAN 内将数据帧发送至正确设备；路由器根据 IP 地址在不同网络间转发数据包；无线接入点 (WAP) 提供 Wi-Fi 连接。
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Star topology: all devices connect to a central switch; if one cable fails, others remain unaffected. Mesh topology: devices interconnect, providing multiple redundant paths and high reliability, but is expensive to cable.
星型拓扑：所有设备都连到中心交换机；一条线缆发生故障时，其余不受影响。网状拓扑：设备互相连接，提供多条冗余路径和高可靠性，但布线成本昂贵。
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Network protocols ensure standardised communication. TCP divides data into packets and reassembles them reliably; IP addresses and routes packets; HTTP/HTTPS transfers web pages; FTP transfers files; SMTP sends emails, POP/IMAP receive emails.
网络协议确保标准化通信。TCP 将数据分装为数据包并可靠重组；IP 编址和路由数据包；HTTP/HTTPS 传输网页；FTP 传输文件；SMTP 发送电子邮件，POP/IMAP 接收邮件。
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The TCP/IP layered model: Application layer (protocols like HTTP, SMTP), Transport layer (TCP error handling), Internet layer (IP addressing/routing), Link layer (physical hardware, MAC). Layering simplifies development and troubleshooting.
TCP/IP 分层模型：应用层（HTTP、SMTP 等协议）、传输层（TCP 差错处理）、网际层（IP 寻址/路由）、链路层（物理硬件、MAC）。分层简化了开发和故障排查。
6. Network Security | 网络安全
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Malware threats: virus (attaches to legitimate files, spreads when executed), worm (self-replicates across networks without user action), trojan (disguised as useful software), ransomware (encrypts user files and demands payment).
恶意软件威胁：病毒（附着于合法文件，执行时传播）、蠕虫（无需用户操作便在网络中自我复制）、木马（伪装成有用软件）、勒索软件（加密用户文件以勒索赎金）。
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Other cyber threats: phishing (fraudulent emails mimicking trusted sources to steal credentials), social engineering (manipulating individuals to divulge confidential information), brute-force attacks (systematic trial of all passwords), Denial of Service (DoS) floods a server with traffic to disrupt service, SQL injection inserts malicious SQL statements into input fields to manipulate databases.
其他网络威胁：网络钓鱼（仿冒可信来源的欺诈邮件以窃取凭证）、社会工程（操纵个人以泄露机密信息）、暴力攻击（系统性地尝试所有密码）、拒绝服务 (DoS) 通过大量流量淹没服务器以中断服务、SQL 注入将恶意 SQL 语句插入输入字段以操控数据库。
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Prevention methods: anti-malware software to detect and remove malicious programs; firewalls monitor and filter incoming/outgoing network traffic based on rules; user access levels restrict data access; strong password policies and two-factor authentication; encryption (e.g., WPA2) protects data in transit; penetration testing simulates attacks to identify vulnerabilities.
预防方法：反恶意软件检测并移除恶意程序；防火墙根据规则监控和过滤进出网络流量；用户权限级别限制数据访问；强密码策略和双重认证；加密（如 WPA2）保护传输中的数据；渗透测试模拟攻击以识别漏洞。
7. Systems Software | 系统软件
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The operating system (OS) manages hardware resources: processor scheduling (multit
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