📚 Year 9 Edexcel Computer Science: Core Knowledge Review | Year 9 Edexcel 计算机：核心知识点梳理
Year 9 Computer Science lays the groundwork for understanding how digital systems work and how to solve problems using computational thinking. This article revisits the core topics, from hardware and binary to programming and networks, to help you consolidate knowledge and prepare for further study.
九年级计算机课程为理解数字系统的工作原理以及如何运用计算思维解决问题奠定基础。本文回顾从硬件、二进制到编程和网络等核心主题，帮助你巩固知识，并为后续学习做好准备。
1. Computer Systems Overview | 计算机系统概述
A computer system is a combination of hardware and software that processes data. Hardware includes physical components like the CPU and memory, while software refers to the programs and instructions that control the hardware.
计算机系统是处理数据的硬件与软件的结合体。硬件包括中央处理器和内存等物理组件，软件则指控制硬件的程序与指令。
Input devices gather data, the processor carries out instructions, and output devices present results. The operating system manages resources and provides a user interface.
输入设备采集数据，处理器执行指令，输出设备呈现结果。操作系统管理资源并提供用户界面。
2. The Central Processing Unit (CPU) | 中央处理器 (CPU)
The CPU is the 'brain' of the computer, executing instructions at incredible speed. It follows the fetch–decode–execute cycle: it fetches an instruction from memory, decodes it to determine the operation, and then executes it.
中央处理器是计算机的“大脑”，以极快的速度执行指令。它遵循取指—译码—执行周期：从内存中取出指令，译码以确定操作，然后执行。
Key components include the Control Unit (CU) that directs operations, the Arithmetic Logic Unit (ALU) that performs calculations and logic operations, and registers that temporarily hold data and instructions. The clock speed, measured in gigahertz (GHz), determines how many cycles per second the CPU can perform.
关键组件包括负责指挥操作的控制单元、执行算术与逻辑运算的算术逻辑单元，以及临时存放数据和指令的寄存器。时钟频率以吉赫（GHz）为单位，决定 CPU 每秒可执行的周期数。
3. Memory and Storage | 内存与存储设备
Primary memory includes RAM (Random Access Memory) and ROM (Read Only Memory). RAM is volatile, meaning it loses its contents when power is off; it holds the data and programs currently in use. ROM is non‑volatile and stores firmware, such as the boot instructions.
主存储器包括随机存取存储器 (RAM) 和只读存储器 (ROM)。RAM 是易失性的，断电后内容会丢失；它存放当前正在使用的数据和程序。ROM 是非易失性的，存储固件，如启动指令。
Secondary storage provides permanent storage. Hard disk drives (HDDs) use magnetic platters, while solid‑state drives (SSDs) use flash memory with no moving parts, offering faster access. Optical discs and USB flash drives are also common.
辅助存储器提供永久存储。硬盘驱动器 (HDD) 使用磁性盘片，而固态驱动器 (SSD) 使用无移动部件的闪存，访问速度更快。光盘和 U 盘也很常见。
4. Input and Output Devices | 输入与输出设备
Input devices send data to the computer. Examples include keyboards, mice, touchscreens, microphones, and sensors such as temperature or light sensors. Output devices receive data from the computer and present it to the user: monitors, printers, speakers, and actuators.
输入设备向计算机发送数据。例子包括键盘、鼠标、触摸屏、麦克风以及温度或光线传感器等。输出设备从计算机接收数据并呈现给用户：显示器、打印机、扬声器和执行器。
Some devices can be both input and output, like a touchscreen or a network card. In embedded systems, input and output are often tailored to specific tasks.
一些设备既是输入设备又是输出设备，例如触摸屏或网卡。在嵌入式系统中，输入和输出常针对特定任务定制。
5. Binary and Data Representation | 二进制与数据表示
Computers use binary, a base‑2 number system with digits 0 and 1. Each binary digit is called a bit. Decimal (denary) numbers can be converted to binary by writing powers of 2: 128, 64, 32, 16, 8, 4, 2, 1 for an 8‑bit number.
计算机使用二进制，即用数字 0 和 1 的二进数系统。每个二进制位称为一个比特。十进制数可以通过写出 2 的幂转换为二进制：对于 8 位数依次是 128, 64, 32, 16, 8, 4, 2, 1。
For example, to represent denary 42 in 8‑ 8 + 0×64 + 1×32 + 0×16 + 1×8 + 0×4 + 1×2 + 0×1 = 00101010₂. The subscript 2 indicates base‑2.
例如，将十进制 42 表示为 8 位二进制：0×128 + 0×64 + 1×32 + 0×16 + 1×8 + 0×4 + 1×2 + 0×1 = 00101010₂。下标 ₂ 表示二进制。
Text is represented using character codes such as ASCII, where each character has a unique 7‑bit or 8‑bit binary number. Images can be stored as bitmaps, where each pixel’s colour is encoded in binary. Sound is sampled at intervals and the amplitude values are converted to binary.
文本使用 ASCII 等字符编码表示，每个字符对应一个唯一的 7 位或 8 位二进制数。图像可以存储为位图，每个像素的颜色用二进制编码。声音按间隔采样，振幅值转换为二进制。
6. Boolean Logic and Logic Gates | 布尔逻辑与逻辑门
Boolean logic deals with values that are either true (1) or false (0). Logic gates are the building blocks of digital circuits. The AND gate outputs 1 only if both inputs are 1. The OR gate outputs 1 if at least one input is 1. The NOT gate inverts the input.
布尔逻辑处理真 (1) 或假 (0) 值。逻辑门是数字电路的构建模块。与门只有当两个输入都为 1 时才输出 1。或门只要至少一个输入为 1 就输出 1。非门将输入取反。
| A | B | A AND B |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
Truth tables list all possible input combinations and the resulting output. Logic gates can be combined to create more complex circuits, such as half adders used in binary addition.
真值表列出所有可能的输入组合及相应的输出。逻辑门可以组合成更复杂的电路，如用于二进制加法的半加器。
7. Programming Fundamentals: Sequence, Selection, Iteration | 编程基础：顺序、选择、迭代
Every program is built from three control structures. Sequence means statements are executed one after the other in order. Selection allows the program to make decisions, using if‑else statements. Iteration repeats a block of code, either a fixed number of times (count‑controlled) or until a condition is met (condition‑controlled).
每个程序都由三种控制结构构建而成。顺序意味着语句按先后次序逐条执行。选择允许程序做出判断，使用 if‑else 语句。迭代重复执行一段代码，可以是固定次数 (计数控制) 或直到条件满足 (条件控制)。
A simple example in pseudocode: 'IF temperature > 30 THEN output "Hot" ELSE output "OK"'. This illustrates selection. A FOR loop that runs 5 times is count‑controlled iteration.
简单的伪代码示例：'IF temperature > 30 THEN output "Hot" ELSE output "OK"'。这展示了选择结构。运行 5 次的 FOR 循环是计数控制的迭代。
8. Data Types and Variables | 数据类型与变量
Variables are named storage locations that hold values that can change during program execution. Common data types include integer (whole numbers), float (decimal numbers), string (text), and Boolean (true/false). Choosing the right data type ensures the program uses memory efficiently and behaves as expected.
变量是命名的存储位置，保存程序执行期间可改变的值。常见数据类型包括整型 (整数)、浮点型 (小数)、字符串 (文本) 和布尔型 (真/假)。选用正确的数据类型可确保程序高效使用内存并按预期运行。
Assignment gives a variable a value, for example score = 0. Operations such as addition and concatenation depend on the data type. Type conversion may be needed when mixing types.
赋值语句给变量一个值，例如 score = 0。加法和拼接等运算取决于数据类型。当混合不同类型时可能需要进行类型转换。
9. Algorithmic Thinking and Flowcharts | 算法思维与流程图
An algorithm is a step‑by‑step set of instructions to solve a problem. Algorithmic thinking involves breaking down problems, recognising patterns, and creating a logical sequence of steps. Algorithms can be expressed in pseudocode or flowcharts.
算法是逐步解决问题的一组指令。算法思维包括分解问题、识别模式并创建逻辑步骤序列。算法可以用伪代码或流程图表示。
Flowcharts use standard symbols: ovals for start/end, parallelograms for input/output, rectangles for processes, diamonds for decisions, and arrows for flow direction. Drawing a flowchart before coding helps visualise the logic and reduces errors.
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，矩形表示处理，菱形表示判断，箭头表示流向。在编码前绘制流程图有助于直观理解逻辑并减少错误。
10. Computer Networks Basics | 计算机网络基础
A network connects computers and devices to share resources and communicate. A Local Area Network (LAN) covers a small area like a school, while a Wide Area Network (WAN) spans large geographical distances, such as the internet. Networks can be wired (Ethernet) or wireless (Wi‑Fi).
网络将计算机和设备连接起来以共享资源和通信。局域网 (LAN) 覆盖学校等小范围区域，广域网 (WAN) 跨越大的地理距离，如互联网。网络可以是有线的 (以太网) 或无线的 (Wi‑Fi)。
Common topologies include star, where each device connects to a central switch, and mesh, where devices are interconnected. Client‑server and peer‑to‑peer are two models of network organisation.
常见拓扑包括星型，每个设备连接到中央交换机；以及网状型，设备相互连接。客户机‑服务器和点对点是两种网络组织模型。
11. Cybersecurity Essentials | 网络安全基础
Cybersecurity protects systems and data from digital attacks. Threats include malware (viruses, worms, ransomware), phishing (fake emails to steal information), and brute‑force attacks that try many passwords. Social engineering exploits human psychology rather than technical weaknesses.
网络安全保护系统和数据免受数字攻击。威胁包括恶意软件 (病毒、蠕虫、勒索软件)、网络钓鱼 (虚假邮件盗取信息) 以及尝试大量密码的暴力攻击。社会工程利用人的心理而非技术弱点。
Defence strategies involve using strong, unique passwords, enabling two‑factor authentication, keeping software updated, and installing firewalls and anti‑malware tools. Regular backups protect against data loss.
防御策略包括使用强而唯一的密码、启用双重认证、保持软件更新，以及安装防火墙和反恶意软件工具。定期备份可防止数据丢失。
12. Ethical and Legal Issues in Computing | 计算机伦理与法律问题
Technology raises ethical questions about privacy, surveillance, and the digital divide. Laws such as the Computer Misuse Act make hacking and unauthorised access illegal. The Data Protection Act controls how personal data can be collected and used.
技术引发了关于隐私、监控和数字鸿沟的伦理问题。诸如《计算机滥用法》等法律将黑客攻击和未经授权的访问定为非法。《数据保护法》控制个人数据的收集和使用方式。
Copyright and intellectual property law protect creators' rights. Plagiarism and software piracy are both illegal and unethical. Understanding these issues helps students use technology responsibly.
版权和知识产权法保护创作者的权益。抄袭和软件盗版既违法又不道德。理解这些问题有助于学生负责任地使用技术。
Published by TutorHao | Computer Science Revision Series | aleveler.com
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