📚 Year 9 WJEC Computer Science: Core Concepts Revision | Year 9 WJEC 计算机科学：核心知识点梳理
This article brings together all the essential topics covered in a typical Year 9 WJEC Computer Science course. From the basic building blocks of a computer to how data is represented and how we write algorithms, every section is designed to reinforce your understanding in both English and Chinese. Use this guide to review key concepts, fill gaps in your knowledge, and prepare confidently for class tests or end‑of‑year exams.
本文整理了 Year 9 WJEC 计算机科学课程中所有核心知识点。从计算机的基本组成部件到数据的表示方式，再到如何编写算法，每个小节都以中英双语搭配呈现，帮助你加深理解。你可以用这篇指南回顾重点、查漏补缺，为课堂测验或年终考试做好充分准备。
1. Computer Systems: Hardware and Software | 计算机系统：硬件与软件
A computer system is made up of two main parts: hardware and software. Hardware refers to any physical component you can touch, while software is the set of instructions that tells the hardware what to do.
计算机系统由两个主要部分组成：硬件和软件。硬件指所有你可以触摸到的物理组件，软件则是告诉硬件该做什么的指令集合。
Typical hardware includes the central processing unit (CPU), main memory (RAM), storage drives, and input/output devices. Software can be divided into system software — such as the operating system — and application software like word processors, web browsers, or games.
典型的硬件包括中央处理器（CPU）、主存储器（RAM）、存储驱动器和输入/输出设备。软件可分为系统软件（例如操作系统）和应用软件（如文字处理器、网络浏览器或游戏）。
Without software, hardware would have no instructions to follow. Without hardware, software could not be executed. They depend on each other to create a functioning computer system.
没有软件，硬件就没有指令可执行；没有硬件，软件也无法运行。两者互相依赖，共同构成一个可用的计算机系统。
2. The CPU and Main Memory | 中央处理器与主存储器
The CPU, often called the 'brain' of the computer, carries out instructions using a repeated cycle known as the fetch–decode–execute cycle. It fetches an instruction from memory, decodes it to understand what is required, and then executes it.
CPU 常被称为计算机的“大脑”，它通过一个叫做“取指–译码–执行”的循环重复完成指令。它从内存中取出指令，译码以理解需要做什么，然后执行该指令。
Main memory, or RAM (Random Access Memory), stores the data and programs that the CPU is currently using. RAM is volatile, meaning it loses all information when the power is turned off.
主存储器也叫 RAM（随机存取存储器），用来存放 CPU 当前正在使用的数据和程序。RAM 是易失性的，也就是说一旦断电，里面的所有信息都会丢失。
In contrast, secondary storage (such as a hard disk or solid‑state drive) keeps data permanently. A computer also contains ROM (Read Only Memory), which stores essential startup instructions and is non‑volatile.
相比之下，辅助存储器（如硬盘或固态硬盘）可以永久保存数据。计算机中还有 ROM（只读存储器），里面存有开机必需的基本指令，它是非易失性的。
3. Input and Output Devices | 输入与输出设备
Input devices allow users to send data, commands, and signals to a computer. Common examples include the keyboard, mouse, touchscreen, microphone, and sensors.
输入设备让用户能够把数据、指令和信号发送给计算机。常见的例子有键盘、鼠标、触摸屏、麦克风和各类传感器。
Output devices take information from the computer and present it to the user. Monitors, printers, speakers, and headphones are all output devices. Some devices, like a touchscreen, can act as both input and output.
输出设备从计算机中获取信息并将其呈现给用户。显示器、打印机、扬声器和耳机都是输出设备。有些设备（比如触摸屏）可以同时充当输入和输出设备。
When choosing an input or output device, we consider factors such as speed, accuracy, user convenience, and suitability for the task — for example, a scanner is ideal for digitising printed photographs.
在选择输入或输出设备时，我们会考虑速度、准确度、用户便利性以及是否适合该任务——例如，扫描仪非常适用于将纸质照片数字化。
4. Binary and Data Representation | 二进制与数据表示
All data inside a computer is stored and processed as binary numbers — sequences of 0s and 1s. Each binary digit is called a bit. A group of 8 bits forms a byte, which can represent 256 different values.
计算机内部的所有数据都以二进制数的形式存储和处理，即一系列的 0 和 1。每个二进制位称为一个比特（bit），8 个比特组成一个字节（byte），可以表示 256 个不同的值。
To convert a binary number to denary (base 10), we use place values that are powers of 2. The rightmost bit represents 2⁰ (1), the next 2¹ (2), then 2² (4), 2³ (8), and so on.
要将二进制数转换为十进制（基数为 10），我们使用 2 的幂作为位权值。最右边的位代表 2⁰（1），下一位代表 2¹（2），然后是 2²（4）、2³（8），依此类推。
Below is a quick conversion table for an 8‑bit binary number:
以下是一个 8 位二进制数的快速转换表：
| Binary Digit (bit) | Place Value (2ⁿ) | Denary Value (if bit=1) |
|---|---|---|
| 1 | 2⁸ | 128 |
| 0 | 2⁹ | 64 |
| 1 | 2⁵ | 32 |
| 1 | 2⁴ | 16 |
| 0 | 2³ | 8 |
| 1 | 2² | 4 |
| 0 | 2¹ | 2 |
| 1 | 2⁰ | 1 |
The binary number 10110101 above equals 128 + 32 + 16 + 4 + 1 = 181 in denary.
上方的二进制数 10110101 等于 128 + 32 + 16 + 4 + 1 = 181（十进制）。
Text characters are represented using codes such as ASCII, where each letter or symbol gets a unique binary number. Images are split into tiny pixels, each assigned a binary value for its colour. Sound is sampled at regular intervals and each sample is stored as binary data.
文字字符通过 ASCII 编码等方式来表示，每个字母或符号拥有一个唯一的二进制数。图像被分割为微小的像素，每个像素分配一个表示颜色的二进制值。声音则通过定期采样，并将每个采样值存储为二进制数据。
5. Algorithms and Pseudocode | 算法与伪代码
An algorithm is a step‑by‑step set of instructions designed to solve a specific problem. It must be clear, unambiguous, and must always finish (terminate). Algorithms are language‑independent, meaning they can be expressed in plain English, pseudocode, or flowcharts.
算法是一组为解决特定问题而设计的逐步指令。它必须清晰明确、没有歧义，而且必须总是能终止。算法与编程语言无关，可以用自然语言、伪代码或者流程图来表达。
Pseudocode is a way of writing algorithms that resembles real programming code but avoids strict syntax. It uses common keywords such as INPUT, OUTPUT, IF…THEN…ELSE, and WHILE or FOR loops.
伪代码是一种编写算法的方式，它看起来很像真正的程序代码，但避免了严格的语法。它使用常见的关键词，如 INPUT、OUTPUT、IF…THEN…ELSE 以及 WHILE 或 FOR 循环。
For example, an algorithm to decide whether a student has passed or failed might look like this in pseudocode:
例如，一个判断学生是否及格的算法，用伪代码可以写成这样：
INPUT mark
IF mark ≥ 50 THEN
OUTPUT 'Pass'
ELSE
OUTPUT 'Fail'
ENDIF
Testing and tracing algorithms with different inputs helps identify logical errors before any real code is written. Trace tables are often used to track the values of variables step by step.
通过不同的输入测试和追踪算法，有助于在编写实际代码之前发现逻辑错误。通常会使用追踪表来逐步记录变量的值。
6. Introduction to Programming with Python | Python 编程入门
Python is a popular high‑level programming language frequently used in schools. It is easy to read and allows you to put computational thinking into practice. A basic Python program that greets a user might look like this:
Python 是一种在学校里广泛使用的高级编程语言，易于阅读，也便于将计算思维付诸实践。一个简单的问候程序可以是：
name = input('What is your name? ')
print('Hello, ' + name)
Variables store data values that can change as the program runs. Common data types include integers (int), floating‑point numbers (float), strings (str), and Boolean values (bool).
变量用于存储程序运行时可以变化的数据值。常见的数据类型包括整型（int）、浮点型（float）、字符串（str）和布尔值（bool）。
Selection allows a program to make decisions. In Python, we use if, elif, and else. Iteration lets us repeat a block of code — for loops are used when we know the number of repetitions, while while loops repeat as long as a condition is true.
选择结构能让程序做出决策。在 Python 中，我们使用 if、elif 和 else。迭代结构可以重复执行一段代码：for 循环用于已知重复次数的情况，while 循环则在条件为真的情况下一直重复。
Programmers must also handle errors carefully. Syntax errors occur when the code breaks the language’s rules; logic errors occur when the code runs but produces the wrong result. Debugging and testing are therefore essential skills.
程序员还必须小心处理错误。语法错误发生在代码违反语言规则时；逻辑错误则是指代码虽然能运行，但给出了错误的结果。因此，调试和测试是必不可少的技能。
7. Introduction to Computer Networks | 计算机网络入门
A computer network connects two or more devices so they can share data and resources. Networks can be wired (using Ethernet cables) or wireless (using Wi‑Fi or Bluetooth).
计算机网络将两台或更多设备连接在一起，使它们可以共享数据和资源。网络可以是有线的（使用以太网线缆），也可以是无线的（使用 Wi‑Fi 或蓝牙）。
A Local Area Network (LAN) covers a small geographical area, such as a school or an office building. A Wide Area Network (WAN) connects devices across a large area — the internet is the largest WAN in the world.
局域网（LAN）覆盖较小的地理区域，例如一所学校或一栋办公楼。广域网（WAN）则跨越大范围连接设备——互联网就是世界上最大的广域网。
Common network hardware includes routers, switches, and hubs. A router connects different networks together, often linking a home network to the internet. Switches connect devices within the same network and direct data intelligently to the correct destination.
常见的网络硬件包括路由器、交换机和集线器。路由器连接不同的网络，经常将家庭网络与互联网相连。交换机则在同一个网络内连接设备，并将数据智能地导向正确目的地。
The client‑server model is typical for many online services: a client (like a web browser) requests a web page, and the server sends back the requested files. In a peer‑to‑peer network, all computers have equal status and can share files directly without a central server.
客户端–服务器模型在许多在线服务中很典型：客户端（如浏览器）请求一个网页，服务器发回所请求的文件。在对等网络中，所有计算机地位平等，可以直接共享文件而无须中央服务器。
8. Cybersecurity and Digital Ethics | 网络安全与数字伦理
Cybersecurity is about protecting systems, networks, and data from digital attacks. Common threats include malware (viruses, worms, ransomware), phishing scams that trick users into revealing personal information, and brute‑force attacks that guess passwords.
网络安全关乎保护系统、网络和数据免受数字攻击。常见威胁包括恶意软件（病毒、蠕虫、勒索软件）、诱骗用户泄露个人信息的网络钓鱼（phishing），以及试图猜解密码的暴力攻击。
Strong passwords, two‑factor authentication, regular software updates, and firewalls are basic but powerful defences. Users should also be cautious about opening email attachments from unknown senders.
强密码、双因素认证、定期软件更新和防火墙都是基本而强大的防护措施。用户还应谨慎对待来自未知发件人的电子邮件附件。
Digital ethics focuses on the responsible use of technology. This includes respecting copyright by not illegally downloading or sharing copyrighted material, understanding the importance of data privacy, and behaving respectfully online.
数字伦理关注如何负责任地使用技术。这包括尊重版权、不非法下载或分享受版权保护的材料，了解数据隐私的重要性，以及在网上表现出尊重他人的行为。
Cyberbullying and spreading misinformation are serious issues. The Computer Misuse Act and the General Data Protection Regulation (GDPR) are two UK laws that help protect individuals and data, and breaking them can have severe consequences.
网络欺凌和传播虚假信息是严重的问题。《计算机滥用法》和《通用数据保护条例》（GDPR）是英国两部有助于保护个人和数据安全的法律，违反这些法律可能带来严重后果。
Published by TutorHao | Computer Science Revision Series | aleveler.com
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