📚 Year 11 CCEA Computer Science: Key Concepts Overview | Year 11 CCEA 计算机：核心知识点梳理
Year 11 CCEA Computer Science builds the foundation for understanding how computer systems work, how data is represented, how networks communicate and how software is designed. This revision guide brings together the essential knowledge points you need to master, with clear English-Chinese explanations to reinforce your learning.
Year 11 CCEA 计算机课程为你理解计算机系统的工作原理、数据的表示方式、网络的通信机制及软件的设计方法打下基础。这份复习指南汇集了你必须掌握的核心知识点，并通过清晰的中英双语解释帮助你巩固所学内容。
1. Computer Systems Architecture | 计算机系统架构
A computer system consists of hardware and software. The physical components include input devices (e.g. keyboard, mouse), output devices (e.g. monitor, printer) and the system unit that houses the central processing unit (CPU), memory and storage.
计算机系统由硬件和软件组成。物理部件包括输入设备（如键盘、鼠标）、输出设备（如显示器、打印机）以及容纳中央处理器（CPU）、内存和存储设备的系统主机。
The CPU is the 'brain' that runs the fetch-decode-execute cycle. It contains the Arithmetic Logic Unit (ALU) for calculations, the Control Unit (CU) for directing operations and registers for high-speed temporary storage.
CPU 是执行“取指–译码–执行”循环的大脑。它包括负责运算的算术逻辑单元（ALU）、指挥操作的控制器（CU）以及用于高速暂存的寄存器。
Key registers in Von Neumann architecture include the Program Counter (PC), Memory Address Register (MAR), Memory Data Register (MDR) and Current Instruction Register (CIR). Address bus, data bus and control bus carry signals between components.
冯·诺依曼架构中的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）和当前指令寄存器（CIR）。地址总线、数据总线和控制总线在各部件之间传递信号。
| Register | Function | 寄存器 | 功能 |
| PC | Holds address of next instruction | PC | 存放下一条指令的地址 |
| MAR | Holds address to be read/written | MAR | 存放要读写的内存地址 |
| MDR | Holds data transferred to/from memory | MDR | 存放与内存之间传输的数据 |
| CIR | Stores the instruction currently being executed | CIR | 存储当前正在执行的指令 |
2. Memory and Storage | 内存与存储
Primary memory includes RAM (volatile, read-write) and ROM (non-volatile, typically stores boot instructions). RAM holds the OS, programs and data in use; its contents are lost when power is off.
主存储器包括 RAM（易失性，可读写）和 ROM（非易失性，通常存放引导指令）。RAM 保存正在使用的操作系统、程序和数据，断电后内容会丢失。
Virtual memory uses part of the hard disk as if it were RAM when physical RAM is full. It prevents crashes but is much slower than real RAM.
当物理内存不足时，虚拟内存将硬盘的一部分当作 RAM 来用。它可以避免系统崩溃，但速度远慢于真实的 RAM。
Secondary storage is non-volatile and stores data permanently. Common types are magnetic hard disks (large, cheap, slower), solid-state drives (fast, durable, more expensive) and optical discs (portable, low capacity).
辅助存储器非易失，永久保存数据。常见类型有磁性硬盘（容量大、便宜、较慢）、固态硬盘（速度快、耐用、较贵）和光盘（便携、容量小）。
byte ≈ 10⁶ bytes, etc. Storage is often measured using binary prefixes: 1 KiB = 2¹⁰ bytes.
数据单位：一个比特是二进制位；1 半字节 = 4 位；1 字节 = 8 位。千字节 ≈ 10³ 字节，兆字节 ≈ 10⁶ 字节等。存储容量常使用二进制前缀：1 KiB = 2¹⁰ 字节。
3. Data Representation – Numbers | 数据表示 – 数字
number like 1101₂ represents the decimal value (1 × 8) + (1 × 4) + (0 × 2) + (1 × 1) = 13.
计算机使用二进制（基数为 2），只用 0 和 1。二进制数如 1101₂ 表示的十进制值为 (1 × 8) + (1 × 4) + (0 × 2) + (1 × 1) = 13。
is a compact way to show binary: each hex digit represents 4 bits. E.g. 1011 1110₂ = BE₁₆.
十六进制（基数为 16）使用数字 0–9 和字母 A–F。它是显示二进制的紧凑方式：每个十六进制位表示 4 个比特。例如 1011 1110₂ = BE₁₆。
Negative numbers can be represented using sign and magnitude, two's complement. In two's complement the most significant bit is negative, making -128 in 8 bits. Binary addition may cause overflow.
负数可以用符号与数值或二补码表示。在二补码中最高位为负值，8 位中可表示 −128。二进制加法可能导致溢出。
Binary shifts: a left logical shift multiplies by 2 for each shift; a right logical shift divides. Arithmetic right shift preserves the sign bit for negative numbers.
二进制移位：每逻辑左移一次乘以 2；逻辑右移则是整除。算术右移对负数保留符号位。
Left shift: 0011₂ << 2 = 1100₂ (3 × 2² = 12)
4. Data Representation – Text, Images and Sound | 数据表示 – 文本、图像与声音
Characters are represented by numeric codes. ASCII uses 7 bits (0–127) for English letters; extended ASCII uses 8 bits. Unicode supports multiple languages with encodings like UTF-8, using up to 32 bits per character.
字符用数字编码表示。ASCII 用 7 位比特（0–127）表示英文字母；扩展 ASCII 使用 8 位。Unicode 通过 UTF-8 等编码支持多种语言，每个字符最多 32 位。
Bitmap images are made of pixels. Each pixel's colour is defined by a binary value determined by colour depth (bits per pixel). Higher resolution and colour depth increase quality but also file size.
位图图像由像素构成。每个像素的颜色由根据颜色深度（每像素位数）决定的二进制值定义。分辨率和颜色深度越高，质量越好，但文件也越大。
Image file size (bits) = Width × Height × Colour Depth
Vector graphics store instructions to draw shapes (lines, curves, polygons) instead of pixels. They scale without losing quality and often have smaller file sizes than bitmaps for diagrams.
矢量图形存储绘制形状（线条、曲线、多边形）的指令，而非像素。缩放时不失真，用于图表时通常比位图文件更小。
Sound is analog and must be sampled to become digital. Sampling rate (Hz) and bit depth (bits per sample) determine quality. Stereo sound doubles the data because of two channels.
声音是模拟信号，必须采样才能转为数字。采样率（Hz）和位深度（每样本位数）决定音质。立体声因有两个通道，数据量加倍。
Sound file size (bits) = Sampling rate × Bit depth × Duration (s) × Channels
5. Networks and Topologies | 网络与拓扑结构
A network connects computers to share resources. A LAN spans a small area (e.g. school); a WAN covers large geographical areas, using public infrastructure. The Internet is the largest WAN.
网络将计算机连接起来共享资源。LAN 覆盖较小区域（如学校）；WAN 跨广阔地理范围，使用公共基础设施。互联网是最大的 WAN。
Client-server networks have a central server providing services; clients request resources. Peer-to-peer (P2P) networks allow all devices to share directly without a central server, offering simplicity but less security.
客户端–服务器网络有中央服务器提供服务，客户端请求资源。点对点（P2P）网络允许所有设备直接共享，无需中央服务器，结构简单但安全性较低。
Network topologies define layout. Bus topology has a single cable (terminators needed), easy to set up but a break disrupts the whole network. Star topology connects all nodes to a central switch; a cable failure only affects one node, but switch failure brings the network down.
网络拓扑定义布局。总线型使用单根电缆（需终端电阻），安装简单但一处断开整个网络瘫痪。星型将所有节点连到中央交换机；单根电缆故障只影响一个节点，但交换机故障会使全网瘫痪。
Key protocols: TCP/IP is the suite governing internet communication. HTTP/HTTPS handles web pages; FTP transfers files; SMTP, IMAP and POP3 manage email. MAC addresses identify NIC hardware; IP addresses identify devices on a network.
关键协议：TCP/IP 是管理互联网通信的协议栈。HTTP/HTTPS 处理网页；FTP 传输文件；SMTP、IMAP 和 POP3 管理电子邮件。MAC 地址标识网卡硬件；IP 地址标识网络中的设备。
6. Network Security | 网络安全
Malware is malicious software: viruses attach to files and spread when executed; worms self-replicate over networks; Trojans disguise as legitimate programs. Spyware secretly gathers information; ransomware encrypts files and demands payment.
恶意软件是恶意程序：病毒寄附于文件，运行时传播；蠕虫在网络上自我复制；木马伪装成合法程序。间谍软件偷偷收集信息；勒索软件加密文件并勒索赎金。
Social engineering tricks people into giving away confidential information. Phishing uses fake emails or websites; baiting offers infected USBs or free downloads. Shoulder surfing and pretexting are other examples.
社会工程学诱骗人们泄露机密信息。钓鱼攻击使用虚假电子邮件或网站；诱饵攻击提供携带病毒的 U 盘或免费下载。肩窥和假装身份也是常见手段。
Defences include firewalls (filter incoming/outgoing traffic), strong passwords and multi-factor authentication, up-to-date anti-malware software, encryption (e.g. WPA3 for Wi-Fi) and user access levels. Physical security such as locks and biometric scanners also matters.
防御措施包括防火墙（过滤进出流量）、强密码与多因素认证、及时更新的反恶意软件、加密（如 Wi-Fi 的 WPA3）和用户权限级别。门锁和生物识别扫描器等物理安全同样重要。
7. System Software and Utility Software | 系统软件与实用软件
System software manages hardware and provides a platform for applications. The operating system (OS) performs memory management, multitasking, peripheral management, file management and security, and provides a user interface (GUI or CLI).
系统软件管理硬件并为应用程序提供平台。操作系统（OS）执行内存管理、多任务处理、外设管理、文件管理和安全功能，并提供用户界面（图形界面或命令行界面）。
Utility software maintains and optimises the computer. Disk defragmentation rearranges fragmented files on magnetic drives to improve speed; backup utilities create copies of data; compression reduces file size for storage or transmission.
实用软件维护和优化计算机。磁盘碎片整理重新排列磁性硬盘上的文件碎片以提升速度；备份实用程序创建数据副本；压缩可减小文件体积，便于存储或传输。
Other utilities include encryption tools (scramble data to protect it), anti-virus (detect and remove malware), disk cleanup (remove temporary files) and firewall software. Application software, by contrast, helps users perform specific tasks like word processing.
其他实用程序包括加密工具（打乱数据以保护信息）、反病毒软件（检测和清除恶意软件）、磁盘清理（删除临时文件）和防火墙软件。相比之下，应用软件帮助用户完成文字处理等具体任务。
8. Programming Concepts | 编程概念
Programs are built from three basic constructs: sequence (instructions execute in order), selection (if-else, switch-case) and iteration (while, for, do-while/repeat-until loops). These form the logic of any algorithm.
程序由三种基本结构构成：顺序（指令依次执行）、选择（if-else、switch-case）和迭代（while、for、do-while/repeat-until 循环）。它们构成了所有算法的逻辑基础。
loat), Boolean, character and string. Type casting converts one type to another, e.g. int('5') → 5.
变量存储可变值；常量保存固定值。标准数据类型包括整型、实数（浮点）、布尔型、字符和字符串。类型转换可将一种类型转为另一种，如 int('5') → 5。
Arrays hold multiple values of the same type in a sequence. 1D arrays are like lists; 2D arrays work like tables, accessed via row and column indices. String manipulation includes finding length, substrings and concatenation.
数组按顺序存放多个同类型数据。一维数组类似列表；二维数组类似表格，通过行、列索引访问。字符串操作包括求长度、获取子串和拼接。
Subprograms break code into manageable parts: procedures perform a task without returning a value, functions return a result. Parameters can be passed by value (copy) or by reference (original variable).
子程序将代码划分成可管理的部分：过程执行任务但不返回值，函数返回一个结果。参数可以按值传递（复制）或按引用传递（操作原变量）。
Common algorithms: linear search checks each item until found; binary search halves a sorted list repeatedly. Bubble sort compares adjacent items and swaps if needed; insertion sort builds a sorted list one element at a time.
常见算法：线性搜索逐个检查直到找到；二分查找在有序列表中反复对半查找。冒泡排序比较相邻项并在需要时交换；插入排序每次将一个元素插入已排好序的列表。
9. Ethical, Legal and Environmental Issues | 伦理、法律与环境问题
The Data Protection Act 2018 (UK GDPR) governs how personal data is collected, stored and used. Organisations must follow principles like lawfulness, fairness, transparency and data minimisation. Individuals have rights to access and correct their data.
《2018 年数据保护法》（英国 GDPR）规范个人数据的收集、存储和使用。机构必须遵守合法性、公平性、透明度和数据最小化等原则。个人有权访问和更正自己的数据。
The Computer Misuse Act 1990 makes unauthorised access to computer material (hacking), intent to commit further offences and impairing operation of a system (e.g. viruses) illegal.
《1990 年计算机滥用法》将未经授权访问计算机资料（黑客）、意图实施进一步犯罪以及破坏系统运行（如病毒）等行为定为非法。
Copyright and intellectual property protect software, music and other digital content. Open-source software allows users to view and modify code, while proprietary software restricts access. Piracy and plagiarism are serious offences.
版权和知识产权保护软件、音乐及其他数字内容。开源软件允许用户查看和修改代码，而专有软件限制访问。盗版和剽窃是严重违法行为。
Environmental concerns involve e-waste (discarded electronic devices), energy consumption of data centres, and the digital divide – the gap between those who have access to technology and those who do not. Responsible use includes recycling devices and developing energy-efficient hardware.
环境问题涉及电子垃圾（废弃的电子设备）、数据中心的能源消耗以及数字鸿沟——能够获取技术的人群与无法获取的人群之间的差距。负责任的使用包括回收设备和开发节能硬件。
10. Exam Preparation and Key Tips | 备考与关键技巧
Start revision early and create a topic checklist. Use past CCEA papers to understand question styles and command terms like 'describe', 'explain', 'compare' and 'evaluate'. Practise writing clear, structured answers under timed conditions.
尽早开始复习，制作知识点清单。练习历年 CCEA 真题，理解“描述”、“解释”、“比较”和“评价”等指令词。在限时条件下练习写出清晰、结构分明的答案。
In data representation questions, always show conversion steps and use correct units. For programming and algorithm questions, draw flowcharts carefully and use consistent pseudocode. Check for boundary conditions and off-by-one errors in loops.
在数据表示题目中，务必展示换算步骤并使用正确单位。对于编程和算法题，仔细绘制流程图并使用一致的伪代码。检查循环中的边界条件和“差 1”错误。
Stay calm, manage your time and read the whole paper before you start writing. For long-answer questions, PEE (point-evidence-explanation) or a similar framework helps you stay focused and earn full marks.
保持冷静，管理好时间，动笔前通读整份试卷。对于长答题，使用“观点–证据–解释”（PEE）或类似的框架有助于保持条理并拿到满分。
Published by TutorHao | Computer Science Revision Series | aleveler.com
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