AS AQA Computer Science: Core Knowledge Review | AS AQA 计算机：核心知识点梳理

📚 AS AQA Computer Science: Core Knowledge Review | AS AQA 计算机：核心知识点梳理

This article provides a structured overview of the essential topics for the AS AQA Computer Science specification. It covers the core areas from data representation and hardware to programming paradigms and ethical considerations, ensuring you have a solid foundation for your revision.

本文为 AS AQA 计算机科学课程的核心主题提供结构化概览。内容涵盖从数据表示、硬件到编程范式与伦理考量的关键领域，确保你打下扎实的复习基础。

1. Number Systems and Data Representation | 数制与数据表示

Computers use binary (base-2) to represent all data. Understanding how numbers, text, images, and sound are encoded is fundamental. Positive integers are represented as pure binary, while negative integers often use two’s complement for efficient arithmetic. Real numbers are stored using floating-point representation (mantissa and exponent), which balances range and precision but introduces rounding errors.

计算机使用二进制（基数为 2）表示所有数据。理解数字、文本、图像和声音如何编码是基础。正整数表示为纯二进制，而负整数常使用补码以便高效运算。实数则通过浮点表示法（尾数和指数）存储，在范围与精度之间取得平衡，但会引入舍入误差。

Binary addition and subtraction; overflow and underflow.
二进制加减法；溢出和下溢。
Hexadecimal as a shorthand for binary; converting between denary, binary, and hex.
十六进制作为二进制的简写；十进制、二进制和十六进制之间的转换。
Character sets: ASCII (7-bit), extended ASCII, and Unicode (supports global languages).
字符集：ASCII（7 位）、扩展 ASCII 和 Unicode（支持全球语言）。
Bitmap images: pixels, resolution, colour depth, file size = width × height × bit depth.
位图图像：像素、分辨率、色彩深度，文件大小 = 宽 × 高 × 位深。
Sound sampling: sample rate, sample resolution, Nyquist theorem. File size = rate × resolution × duration × channels.
声音采样：采样率、采样分辨率、奈奎斯特定理。文件大小 = 采样率 × 分辨率 × 时长 × 声道数。

2. Computer Hardware and Architecture | 计算机硬件与体系结构

The von Neumann architecture underpins most modern computers, featuring a single shared memory for data and instructions. Key components include the CPU (with control unit, arithmetic logic unit, and registers), main memory (RAM and ROM), and input/output controllers. The fetch-decode-execute cycle describes how instructions are processed; the program counter (PC) holds the address of the next instruction, the memory address register (MAR) and memory data register (MDR) facilitate memory access, and the current instruction register (CIR) stores the instruction being executed.

冯·诺依曼体系结构是大多数现代计算机的基础，其特点是数据和指令共享单一内存。关键组件包括 CPU（含控制单元、算术逻辑单元和寄存器）、主存储器（RAM 和 ROM）以及输入/输出控制器。取指-译码-执行周期描述了指令处理过程；程序计数器（PC）存放下一条指令的地址，存储器地址寄存器（MAR）和存储器数据寄存器（MDR）协助访问内存，当前指令寄存器（CIR）存储正在执行的指令。

Factors affecting CPU performance: clock speed, number of cores, cache size.
影响 CPU 性能的因素：时钟速度、核心数量、缓存大小。
Secondary storage: magnetic (HDD, high capacity, mechanical), optical (CD/DVD, portable), solid-state (SSD, fast, no moving parts). Characteristics: capacity, speed, portability, durability, cost.
辅助存储器：磁性（HDD，大容量，机械式）、光学（CD/DVD，便于携带）、固态（SSD，速度快，无移动部件）。特性：容量、速度、可携带性、耐用性、成本。
Embedded systems: dedicated microprocessors within larger devices (e.g., washing machines, traffic lights), often using ROM for firmware.
嵌入式系统：大型设备中的专用微处理器（如洗衣机、交通灯），通常使用 ROM 存储固件。

3. Systems Software | 系统软件

Systems software manages hardware resources and provides a platform for application software. The operating system (OS) performs memory management (paging, segmentation, virtual memory), process scheduling (round-robin, priority-based, multi-tasking), file management, and handling of interrupts. Utility programs maintain the system: disk defragmentation reorganises fragmented files on HDDs to improve access speed, backup software creates copies of data, and compression utilities reduce file size.

系统软件管理硬件资源，并为应用软件提供平台。操作系统（OS）执行内存管理（分页、分段、虚拟内存）、进程调度（轮转法、基于优先级、多任务处理）、文件管理以及中断处理。实用程序负责系统维护：磁盘碎片整理重新组织 HDD 上的碎片文件以提高访问速度，备份软件创建数据副本，压缩实用工具减小文件大小。

Application software vs. systems software; general-purpose vs. custom-written vs. off-the-shelf.
应用软件与系统软件；通用型、定制型与成品软件的区别。
Virtual memory: using hard disk space as extension of RAM when physical memory is full; thrashing occurs when excessive swapping degrades performance.
虚拟内存：物理内存不足时使用硬盘空间作为 RAM 的扩展；当过度交换导致性能下降时即发生抖动。
Interrupts: hardware interrupts (keyboard, mouse) and software interrupts (division by zero); the interrupt service routine (ISR) handles them via the interrupt vector table.
中断：硬件中断（键盘、鼠标）和软件中断（除零）；中断服务例程（ISR）通过中断向量表进行处理。

4. Networking Fundamentals | 网络基础

Networks enable devices to share resources and communicate. Common topologies include star (central switch, easy to manage, single point of failure), bus (single backbone cable, limited number of devices), and mesh (fully or partially connected, high redundancy). Protocols are rules for communication: TCP/IP stack layers (application, transport, internet, network interface) provide reliable data delivery. The internet protocol (IP) handles addressing and routing, while transmission control protocol (TCP) ensures data arrives error-free and in order.

网络使设备能够共享资源并通信。常见拓扑包括星型（中央交换机，易于管理，单点故障）、总线型（单根主干电缆，设备数量有限）和网状（全连接或部分连接，高度冗余）。协议是通信规则：TCP/IP 协议栈的层次（应用层、传输层、网际层、网络接口层）提供可靠的数据交付。互联网协议（IP）负责寻址和路由，而传输控制协议（TCP）确保数据无差错且按序到达。

Client-server vs. peer-to-peer (P2P) models.
客户端-服务器与对等（P2P）模型。
IP addressing: IPv4 (32-bit, dotted decimal, 4.3 billion addresses) and IPv6 (128-bit, hexadecimal, vastly more addresses).
IP 寻址：IPv4（32 位，点分十进制，约 43 亿个地址）和 IPv6（128 位，十六进制，地址数量极大增长）。
Domain name system (DNS) translates domain names to IP addresses.
域名系统（DNS）将域名转换为 IP 地址。
LANs and WANs: LAN covers small geographic area, WAN spans cities/countries; packet switching and circuit switching.
局域网与广域网：局域网覆盖小范围地理区域，广域网跨越城市/国家；分组交换与电路交换。

5. Cybersecurity Essentials | 网络安全要点

Cybersecurity aims to protect systems, networks, and data from digital attacks. Threats include malware (viruses, worms, trojans, ransomware), phishing (deceptive emails to steal credentials), and brute-force attacks. Social engineering exploits human psychology rather than technical flaws. Organisations implement firewalls (packet filtering, stateful inspection) to monitor incoming/outgoing traffic, encryption (symmetric and asymmetric) to secure data, and penetration testing to identify vulnerabilities.

网络安全旨在保护系统、网络和数据免受数字攻击。威胁包括恶意软件（病毒、蠕虫、木马、勒索软件）、网络钓鱼（欺骗性邮件以窃取凭证）和暴力攻击。社会工程学利用人类心理而非技术缺陷。组织实施防火墙（包过滤、状态检测）以监控进出流量，加密（对称与非对称）以保护数据，以及渗透测试以识别漏洞。

Forms of attack: denial of service (DoS), SQL injection, man-in-the-middle.
攻击形式：拒绝服务（DoS）、SQL 注入、中间人攻击。
Prevention methods: access rights, two-factor authentication, security patches, staff training.
预防方法：访问权限、双因素认证、安全补丁、员工培训。
Encryption: Caesar cipher (substitution), symmetric encryption (same key, e.g., AES), asymmetric encryption (public/private key pair, e.g., RSA).
加密：凯撒密码（替换）、对称加密（相同密钥，如 AES）、非对称加密（公钥/私钥对，如 RSA）。
Backup strategies: full, incremental, differential; off-site storage and cloud backups.
备份策略：完整备份、增量备份、差异备份；异地存储和云备份。

6. Data Structures and Abstract Data Types | 数据结构与抽象数据类型

Abstract data types (ADTs) are logical descriptions of data and the operations possible, independent of implementation. Arrays are contiguous memory locations with direct indexing; records group related data of different types together. Queues (FIFO) and stacks (LIFO) are linear structures with restricted access. A stack uses push and pop operations, while a queue uses enqueue and dequeue. These can be implemented using arrays or linked lists.

抽象数据类型（ADT）是对数据及可执行操作的逻辑描述，独立于实现。数组是连续内存位置，支持直接索引；记录将不同类型的相关数据组合在一起。队列（先进先出）和栈（后进先出）是具有受限访问的线性结构。栈使用压入（push）和弹出（pop）操作，队列使用入队和出队操作。它们可用数组或链表实现。

Linked lists: dynamic structures where nodes (data + pointer) point to the next node; efficient insertion and deletion, but sequential access.
链表：动态结构，节点（数据 + 指针）指向下一节点；插入和删除高效，但只能顺序访问。
Trees: binary trees, binary search trees (left child < parent, right child > parent) allow efficient searching, insertion, and deletion.
树：二叉树，二叉搜索树（左子节点 < 父节点，右子节点 > 父节点）支持高效搜索、插入和删除。
Hash tables: maps keys to array indices using a hash function; collisions handled by chaining (linked list at each index) or open addressing.
哈希表：使用哈希函数将键映射到数组索引；冲突通过链地址法（每个索引处建链表）或开放寻址法处理。

7. Algorithms and Problem Solving | 算法与问题求解

An algorithm is a step-by-step procedure to solve a problem. It must be unambiguous, finite, and effective. Common search algorithms include linear search (O(n), works on unsorted data) and binary search (O(log n), requires sorted data). Sorting algorithms: bubble sort (compares adjacent items, O(n²)), insertion sort (builds sorted portion, efficient for small n), and merge sort (divide and conquer, O(n log n)). Understanding time and space complexity helps evaluate efficiency.

算法是解决问题的分步过程，必须无歧义、有限且有效。常见搜索算法包括线性搜索（时间复杂度 O(n)，适用于未排序数据）和二分搜索（O(log n)，要求数据已排序）。排序算法：冒泡排序（比较相邻项，O(n²)）、插入排序（构建已排序部分，对小规模数据高效）和归并排序（分治法，O(n log n)）。理解时间复杂度和空间复杂度有助于评估效率。

Representing algorithms: structured English, flowcharts, pseudocode.
算法表示：结构化英语、流程图、伪代码。
Recursion: a function calls itself; must have a base case to avoid infinite loops.
递归：函数调用自身；必须存在基准情形以避免无限循环。
Modular programming: breaking problems into smaller, manageable subroutines (procedures and functions).
模块化编程：将问题分解为更小、可管理的子程序（过程和函数）。

8. Programming Paradigms and Constructs | 编程范式与结构

Programming paradigms dictate the style of programming. Imperative programming uses sequences, selection (if-else, switch), and iteration (for, while) to control flow. Procedural programming groups instructions into procedures/functions for reusability. Object-oriented programming (OOP) organises code around objects (instances of classes) that encapsulate data (attributes) and behaviour (methods), supporting inheritance, polymorphism, and encapsulation.

编程范式决定了编程风格。命令式编程使用顺序、选择（if-else, switch）和迭代（for, while）来控制流程。过程式编程将指令分组为过程/函数以实现重用。面向对象编程（OOP）围绕对象（类的实例）组织代码，对象封装数据（属性）和行为（方法），支持继承、多态和封装。

Data types: integer, real/float, Boolean, character, string; type casting.
数据类型：整型、实型/浮点型、布尔型、字符型、字符串；类型转换。
Operators: arithmetic (+, -, *, /, MOD, DIV), relational (==, !=, >, <, >=, <=), logical (AND, OR, NOT).
运算符：算术运算符（+、-、*、/、MOD、DIV），关系运算符（==、!=、>、<、>=、<=），逻辑运算符（AND、OR、NOT）。
Passing parameters: by value (copy of data) vs. by reference (address of data).
参数传递：按值传递（数据副本）与按引用传递（数据地址）。
IDE features: editor, compiler/interpreter, debugger, syntax highlighting, auto-completion.
集成开发环境功能：编辑器、编译器/解释器、调试器、语法高亮、自动补全。

9. Software Development Lifecycle | 软件开发生命周期

Developing software follows a lifecycle to manage complexity and ensure quality. The waterfall model is linear: analysis (requirements gathering), design (system architecture, algorithms), implementation (coding), testing (unit, integration, system, alpha/beta), and maintenance (corrective, adaptive, perfective). Agile methodologies (e.g., Scrum) iterate through sprints, delivering incremental working software, emphasising collaboration and adaptability.

软件开发遵循生命周期以管理复杂性并确保质量。瀑布模型是线性的：分析（需求收集）、设计（系统架构、算法）、实现（编码）、测试（单元测试、集成测试、系统测试、alpha/beta 测试）和维护（纠错性、适应性、完善性）。敏捷方法（如 Scrum）通过冲刺迭代进行，交付增量式可用软件，强调协作与适应性。

Types of testing: white-box (tests internal logic), black-box (tests functionality without seeing code), path coverage.
测试类型：白盒测试（测试内部逻辑）、黑盒测试（在不看代码的情况下测试功能）、路径覆盖。
Errors: syntax errors (caught by compiler), logic errors (flawed algorithm), runtime errors (execution-time issues, e.g., division by zero).
错误类型：语法错误（由编译器捕获）、逻辑错误（算法缺陷）、运行时错误（执行时问题，如除零）。
Trace tables track variable states during an algorithm to detect logic errors.
跟踪表记录算法执行期间变量的状态以检测逻辑错误。

10. Ethical, Legal, and Cultural Issues | 伦理、法律与文化问题

The widespread use of computer systems raises significant ethical and legal concerns. Data protection laws (e.g., UK Data Protection Act) regulate the collection, storage, and processing of personal data. The Computer Misuse Act criminalises unauthorised access and hacking. Intellectual property rights cover software licensing (proprietary, open source, shareware). The digital divide refers to the gap between those with and without access to technology, influenced by economic, geographic, and educational factors.

计算机系统的广泛使用引发了重大的伦理与法律问题。数据保护法（如英国数据保护法）规范个人数据的收集、存储和处理。《计算机滥用法》将未经授权的访问和黑客行为定为刑事犯罪。知识产权涵盖软件许可（专有、开源、共享软件）。数字鸿沟指有技术和无技术人群之间的差距，受经济、地理和教育因素影响。

Censorship vs. freedom of speech on the internet; age restrictions and content filtering.
互联网审查与言论自由；年龄限制和内容过滤。
Environmental impact: energy consumption of data centres, e-waste disposal, design for sustainability.
环境影响：数据中心的能源消耗，电子废弃物处理，可持续设计。
Cultural implications: globalisation, loss of local languages, accessibility standards (e.g., screen readers, subtitles).
文化影响：全球化、地方语言流失、无障碍标准（如屏幕阅读器、字幕）。
Professional responsibilities: codes of conduct for IT professionals, whistleblowing, public interest.
职业责任：IT 专业人员行为准则、揭发、公共利益。

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AS AQA Computer Science: Core Knowledge Review | AS AQA 计算机：核心知识点梳理