📚 GCSE OCR Computer Science: End-of-Term Revision Guide | GCSE OCR 计算机：期末复习提纲
This comprehensive revision guide covers the key topics in the OCR GCSE (9-1) Computer Science J277 specification, designed to help you consolidate your learning before the end-of-term assessment. Each section revisits the essential knowledge and understanding required for both Paper 1 (Computer Systems) and Paper 2 (Computational Thinking, Algorithms and Programming). Use this guide to test your recall, identify any weak spots, and structure your final review sessions with confidence.
这份综合复习提纲涵盖了 OCR GCSE (9-1) 计算机科学 J277 大纲的核心主题，旨在帮助你在期末评估前巩固所学。每一节都回顾了试卷一（计算机系统）和试卷二（计算思维、算法与编程）所必需的基本知识与理解。利用本提纲检测你的记忆情况，找出薄弱环节，并自信地规划最后的复习阶段。
1. Systems Architecture | 系统架构
The central processing unit (CPU) fetches, decodes and executes instructions through the Fetch-Decode-Execute cycle. Its performance is determined by clock speed (measured in GHz), number of cores, and cache size — more cores allow parallel processing, while larger cache reduces the need to access slower main memory.
中央处理器（CPU）通过“取指-译码-执行”循环来处理指令。其性能由时钟频率（以 GHz 为单位）、内核数量和缓存大小决定——更多的内核允许并行处理，而更大的缓存则减少访问较慢主存的需求。
Von Neumann architecture stores both data and instructions in the same memory, using shared buses. Key registers include the Program Counter (PC), Memory Address Register (MAR), Memory Data Register (MDR), Accumulator (ACC), and Current Instruction Register (CIR). The Arithmetic Logic Unit (ALU) performs calculations and logical operations, while the Control Unit (CU) directs the flow of data.
冯·诺依曼架构将数据和指令存放在同一内存中，使用共享总线。关键寄存器包括程序计数器（PC）、内存地址寄存器（MAR）、内存数据寄存器（MDR）、累加器（ACC）和当前指令寄存器（CIR）。算术逻辑单元（ALU）执行运算和逻辑操作，控制单元（CU）则指挥数据流。
Embedded systems are dedicated microprocessors within larger devices (e.g., washing machines, microwaves). They are optimised for a single task, making them more reliable, cost-effective and power-efficient than general-purpose computers.
嵌入式系统是位于大型设备（如洗衣机、微波炉）内的专用微处理器。它们针对单一任务进行优化，因此比通用计算机更可靠、更具成本效益且更省电。
2. Memory and Storage | 内存与存储
Primary memory includes RAM (volatile, used for currently running programs and data) and ROM (non-volatile, stores boot instructions and firmware). Virtual memory uses part of the hard disk as temporary RAM when physical memory is full, but it is much slower.
主存包括 RAM（易失性，用于存放当前运行的程序和数据）和 ROM（非易失性，存储启动指令和固件）。当物理内存不足时，虚拟内存将部分硬盘用作临时 RAM，但其速度慢得多。
Secondary storage is non-volatile. Magnetic storage (HDDs) uses spinning platters and is cheap with high capacity. Solid-state storage (SSDs, USB drives) uses flash memory — faster, more durable and silent, but costlier per gigabyte. Optical storage (CDs, DVDs) uses lasers and is useful for portable media distribution. When choosing storage, consider capacity, speed, portability, durability, reliability and cost.
辅助存储器是非易失性的。磁存储（HDD）使用旋转碟片，廉价且容量高。固态存储（SSD、U盘）使用闪存，速度更快、更耐用且安静，但每 GB 成本更高。光存储（CD、DVD）使用激光，适用于便携式媒体分发。选择存储时需考虑容量、速度、便携性、耐用性、可靠性和成本。
Data units: bit, nibble (4 bits), byte (8 bits), kilobyte (KB ≈ 10³ bytes), megabyte (MB), gigabyte (GB), terabyte (TB), petabyte (PB). The binary system uses base 2; capacities are often shown as powers of 2.
数据单位：位（bit）、半字节（nibble，4 bits）、字节（byte，8 bits）、千字节（KB ≈ 10³ bytes）、兆字节（MB）、千兆字节（GB）、太字节（TB）、拍字节（PB）。二进制使用基数 2；容量常以 2 的幂次表示。
3. Computer Networks, Connections and Protocols | 计算机网络、连接与协议
A network allows devices to share resources and communicate. LANs cover a small geographical area; WANs connect LANs over large distances using infrastructure (leased lines, satellites). Factors affecting network performance include bandwidth (data transfer rate), number of users, and transmission media (wired vs wireless).
网络允许设备共享资源并通信。局域网（LAN）覆盖小范围地理区域；广域网（WAN）通过基础设施（专线、卫星）将局域网远距离相连。影响网络性能的因素包括带宽（数据传输速率）、用户数量和传输介质（有线与无线）。
Client-server networks have a central server providing services and resources; clients request them. Peer-to-peer networks have no central server — all devices are equal and share directly, useful for file sharing but harder to manage and secure.
客户端-服务器网络有一台中央服务器提供服务和资源；客户端发出请求。对等（P2P）网络没有中央服务器——所有设备平等并直接共享，适合文件共享但较难管理和保护。
Common hardware: NIC, switch, router, WAP, transmission media (Ethernet cables, fibre optic, wireless). The Internet uses TCP/IP as its protocol stack. TCP breaks data into packets and reassembles them, ensuring reliable delivery; IP handles addressing and routing across networks. HTTP/HTTPS, FTP, SMTP, POP3, IMAP are application-layer protocols.
常见硬件：网卡（NIC）、交换机、路由器、无线接入点（WAP）、传输介质（以太网线、光纤、无线）。互联网使用 TCP/IP 协议栈。TCP 将数据分割为数据包并重新组装，保证可靠传输；IP 负责寻址和跨网路由。HTTP/HTTPS、FTP、SMTP、POP3、IMAP 属于应用层协议。
4. Network Security | 网络安全
Threats include malware (viruses, worms, trojans, ransomware, spyware), phishing (fraudulent emails to steal data), social engineering (manipulating people), brute-force attacks, denial-of-service (DoS) attacks, data interception, and SQL injection (inserting malicious code into database queries).
威胁包括恶意软件（病毒、蠕虫、木马、勒索软件、间谍软件）、网络钓鱼（欺诈邮件窃取数据）、社会工程（操纵人员）、暴力攻击、拒绝服务攻击、数据拦截以及 SQL 注入（将恶意代码插入数据库查询）。
Security measures: penetration testing (ethical hacking to find weaknesses), anti-malware software, firewalls (filter incoming/outgoing traffic), encryption (scrambles data, e.g., HTTPS, WPA2/WPA3), user access levels, strong passwords, and physical security. Regular software updates patch known vulnerabilities.
安全措施：渗透测试（伦理黑客寻找弱点）、反恶意软件、防火墙（过滤进出流量）、加密（打乱数据，如 HTTPS、WPA2/WPA3）、用户访问级别、强密码和物理安全。定期软件更新可修补已知漏洞。
5. System Software | 系统软件
System software manages hardware and provides a platform for application software. The operating system (OS) provides a user interface (GUI, CLI), memory management (allocation and multitasking), peripheral management (drivers), file management, and user management (accounts, access rights).
系统软件管理硬件并为应用软件提供平台。操作系统（OS）提供用户界面（GUI、CLI）、内存管理（分配与多任务）、外设管理（驱动程序）、文件管理以及用户管理（账户、访问权限）。
Utility software performs maintenance tasks: encryption software, defragmentation (reorganises files on HDDs for faster access — not needed for SSDs), compression (lossy reduces file size by removing data; lossless preserves all original data), backup (full, incremental).
实用工具软件执行维护任务：加密软件、碎片整理（重新整理 HDD 上的文件以加快访问速度——SSD 不需要）、压缩（有损压缩通过移除数据减小文件；无损压缩保留所有原始数据）、备份（完整、增量）。
6. Ethical, Legal, Cultural and Environmental Issues | 伦理、法律、文化和环境问题
Computing technologies raise ethical questions around privacy, surveillance, artificial intelligence bias, and digital divide. The Data Protection Act 2018 (incorporating GDPR) governs how personal data may be collected, stored and used — it requires consent, purpose limitation, and data subject rights. Computer Misuse Act 1990 makes unauthorised access, modifications and malware creation illegal.
计算技术引发了隐私、监控、人工智能偏见和数字鸿沟等伦理问题。《2018 年数据保护法》（纳入 GDPR）规范了个人数据的收集、存储和使用——要求获得同意、目的限制并维护数据主体权利。《1990 年计算机滥用法》将未经授权的访问、修改和恶意软件制作定为非法。
Copyright, Designs and Patents Act 1988 protects creators’ intellectual property; using software without a licence is piracy. Creative Commons licences allow creators to share work with specific permissions. The Freedom of Information Act gives public access to information held by public authorities. Environmental impacts include e-waste disposal, energy consumption of data centres, and the carbon footprint of manufacturing devices. The cultural dimension includes changing communication habits, globalisation, and the ‘right to be forgotten’.
《1988 年版权、外观设计和专利法》保护创作者知识产权；无许可证使用软件属于盗版。知识共享（Creative Commons）许可允许创作者以特定权限分享作品。《信息自由法》赋予公众查阅公共机构持有的信息的权利。环境影响包括电子废弃物处理、数据中心能耗以及设备制造的碳足迹。文化层面涉及沟通习惯改变、全球化以及“被遗忘权”。
7. Algorithms | 算法
Algorithms are step-by-step procedures for solving problems. Abstraction removes unnecessary details; decomposition breaks a problem into smaller, manageable sub-problems. Algorithmic thinking involves identifying the steps needed to reach a solution. Search algorithms: linear search checks each element in order (simple but O(n)), binary search works on sorted lists by repeatedly dividing the search interval in half (O(log n)).
算法是解决问题的分步过程。抽象去除不必要细节；分解将问题拆分为更小、可管理的子问题。算法思维涉及识别达成解决方案所需的步骤。搜索算法：线性搜索按顺序检查每个元素（简单但 O(n)）；二分搜索在有序列表中反复将搜索区间减半（O(log n)）。
Sorting algorithms: bubble sort repeatedly swaps adjacent items if they are in the wrong order — intuitive but O(n²); merge sort divides the list, recursively sorts each half, then merges them — O(n log n) and efficient for large data sets. Insertion sort builds the final sorted list one item at a time by inserting each item into its correct position.
排序算法：冒泡排序反复交换顺序错误的相邻项——直观但 O(n²)；归并排序将列表拆分，递归排序每一半，然后合并——O(n log n)，适合大数据集；插入排序一次构建一个排序项，将每一项插入其正确位置。
Flowcharts use standard symbols (ovals for start/end, parallelograms for I/O, diamonds for decisions, rectangles for processes) to represent algorithms visually. Pseudocode uses structured, language-agnostic notation to plan logic without formal syntax.
流程图使用标准符号（椭圆表示开始/结束，平行四边形表示输入/输出，菱形表示判断，矩形表示处理步骤）来直观表示算法。伪代码使用结构化、与语言无关的符号来规划逻辑，无需正式语法。
8. Programming Fundamentals | 编程基础
Key programming constructs: sequence, selection (if, else, switch/case) and iteration (for, while, do-while). Variables store data values; constants hold values that do not change. Data types include integer, real/float, Boolean, character, and string. Type conversion (casting) may be needed when combining different types.
关键编程构造：顺序、选择（if、else、switch/case）和迭代（for、while、do-while）。变量存储数据值；常量保存不变的值。数据类型包括整数、实数/浮点数、布尔型、字符和字符串。组合不同类型时可能需要类型转换（强制转换）。
String manipulation: concatenation (joining strings), slicing (extracting substrings), length, and character indexing. Arrays (and lists in Python) store multiple values under one identifier; two-dimensional arrays resemble tables or grids. File handling: open, read, write, close — data can be stored persistently in text or binary files.
字符串操作：连接（拼接字符串）、切片（提取子串）、长度和字符索引。数组（Python 中为列表）用一个标识符存储多个值；二维数组类似表格或网格。文件处理：打开、读取、写入、关闭——数据可持久存储于文本或二进制文件。
Subprograms: functions (return a value) and procedures (do not return a value) improve modularity, reusability and readability. Parameters pass data into subprograms; local variables exist only inside the subprogram, while global variables are accessible throughout the program — but overuse of globals is discouraged.
子程序：函数（返回值）和过程（不返回值）提高了模块化、可复用性和可读性。参数将数据传入子程序；局部变量仅存在于子程序内，全局变量在整个程序中可访问——但不鼓励过度使用全局变量。
9. Data Representation | 数据表示
Computers use binary (base 2) with bits 0 and 1. Converting between binary, denary (decimal) and hexadecimal (base 16) is essential. Hexadecimal uses digits 0-9 and A-F, making it shorter to represent large binary values (e.g., colour codes).
计算机使用二进制（基 2），位为 0 和 1。在二进制、十进制（基 10）和十六进制（基 16）之间转换是必备技能。十六进制使用数字 0-9 和 A-F，能更简短地表示较大的二进制值（如颜色代码）。
Character encoding: 7-bit ASCII represents 128 characters; extended ASCII uses 8 bits for 256 characters. Unicode (UTF-8, UTF-16) supports tens of thousands of characters from different languages and symbols, enabling global communication but requiring more bits per character.
字符编码：7 位 ASCII 表示 128 个字符；扩展 ASCII 使用 8 位表示 256 个字符。Unicode（UTF-8、UTF-16）支持来自不同语言和符号的数万个字符，支持全球通信，但每个字符需要更多位。
Images are stored as a grid of pixels; each pixel’s colour is represented by a binary code. Colour depth (bits per pixel) determines the number of available colours. Resolution is the number of pixels per image. Higher resolution and colour depth increase file size. Metadata records dimensions, colour depth, and other information. Sound is sampled at regular intervals — sample rate (Hz) and bit depth affect quality and file size.
图像以像素网格存储；每个像素的颜色由二进制码表示。颜色深度（每像素位数）决定可用颜色数。分辨率是每幅图像的像素数。较高的分辨率和颜色深度会增加文件大小。元数据记录尺寸、颜色深度等信息。声音以固定间隔采样——采样率（Hz）和位深度影响质量和文件大小。
Compression: lossy reduces file size by permanently removing some data (e.g., MP3, JPEG); lossless reduces file size without any loss of quality (e.g., PNG, ZIP), suitable for text and program files.
压缩：有损压缩通过永久移除部分数据减小文件（如 MP3、JPEG）；无损压缩在不丢失任何质量的前提下减小文件（如 PNG、ZIP），适用于文本和程序文件。
10. Boolean Logic | 布尔逻辑
Boolean algebra uses TRUE (1) and FALSE (0) with logical operators AND, OR, NOT. Truth tables list all possible input combinations and their output. Logic gates: AND gate (output 1 only if all inputs are 1), OR gate (output 1 if at least one input is 1), NOT gate (inverts input).
布尔代数使用 TRUE（1）和 FALSE（0）以及逻辑运算符 AND、OR、NOT。真值表列出所有可能的输入组合及其输出。逻辑门：与门（仅当所有输入为 1 时输出 1）、或门（至少一个输入为 1 时输出 1）、非门（将输入取反）。
Logic circuits combine gates to perform complex operations. Creating a truth table for a given circuit requires tracing signals through each gate. A logic expression can be simplified using Boolean identities (e.g., De Morgan’s laws) to create cheaper, faster circuits.
逻辑电路组合门以执行复杂操作。为给定电路创建真值表需要通过每个门追踪信号。可使用布尔恒等式（如德摩根定律）简化逻辑表达式，从而构建更廉价、更快的电路。
11. Programming Languages and IDEs | 编程语言与集成开发环境
High-level languages (Python, Java) are human-readable and portable; they must be translated into machine code. Low-level languages include assembly language (mnemonics) and machine code (binary). Compilers translate the entire source code into an executable file before execution; interpreters translate and execute line by line. An assembler converts assembly language into machine code.
高级语言（Python、Java）易于人类阅读且可移植；必须翻译为机器码。低级语言包括汇编语言（助记符）和机器码（二进制）。编译器在执行前将整个源代码翻译为可执行文件；解释器逐行翻译并执行。汇编器将汇编语言转换为机器码。
An Integrated Development Environment (IDE) provides tools such as a code editor (with syntax highlighting), error diagnostics (debugging tools), run-time environment, built-in compiler/interpreter, and breakpoints for stepping through code. These features speed up development and help locate errors.
集成开发环境（IDE）提供代码编辑器（带语法高亮）、错误诊断（调试工具）、运行时环境、内置编译器/解释器以及用于单步执行代码的断点等工具。这些功能加速开发并帮助定位错误。
12. Testing and Defensive Design | 测试与防御式设计
Testing ensures a program works as intended. Iterative testing occurs during development; final/terminal testing happens after completion. Test data should include normal, boundary, invalid, and erroneous inputs. Syntax errors break language rules; logic errors produce incorrect results.
测试确保程序按预期运行。迭代测试在开发过程中进行；最终/终点测试在完成后进行。测试数据应包括正常、边界、无效和错误输入。语法错误违反语言规则；逻辑错误产生错误结果。
Defensive design anticipates misuse and errors: input validation (range check, presence check, format check), authentication (verifying user identity), and maintainable code (comments, indentation, meaningful variable names). Anticipate edge cases to prevent runtime errors.
防御式设计预见误用和错误：输入验证（范围检查、存在检查、格式检查）、身份验证（确认用户身份）以及可维护代码（注释、缩进、有意义的变量名）。预见边缘情况以防止运行时错误。
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