📚 Computing Homework Book 8C: Core Topics Excluding Unit 2 | 计算机作业册8C：核心主题（不含第2单元）
This revision guide brings together the essential topics from Homework Book 8C, excluding Unit 2. It is designed for students who want a clear, exam-focused summary of computer systems, data representation, programming, networks and cybersecurity. Each section pairs an English explanation with a Chinese equivalent so that learners can study bilingually.
本复习指南汇总了作业册8C除第2单元外的核心主题。它面向希望获得清晰、紧扣考试重点总结的学生，涵盖计算机系统、数据表示、编程、网络与网络安全。每节均采用英文与中文对照讲解，便于双语学习。
1. Computer Systems and the CPU | 计算机系统与中央处理器
A computer system consists of hardware and software. Hardware includes the physical components such as the CPU, motherboard, RAM and storage devices. Software refers to the programs and data that instruct the hardware to perform tasks.
计算机系统由硬件和软件组成。硬件包括CPU、主板、内存和存储设备等物理组件。软件是指指挥硬件执行任务的程序和数据。
The CPU, or central processing unit, is often called the brain of the computer. It processes instructions by repeatedly carrying out the fetch-decode-execute cycle. The clock speed, measured in gigahertz (GHz), indicates how many cycles the CPU can complete per second.
CPU，即中央处理器，常被称为计算机的大脑。它通过反复执行「取指-译码-执行」周期来处理指令。时钟速度以吉赫兹（GHz）为单位，表示CPU每秒可以完成多少个周期。
- Hardware: CPU, RAM, hard disk, motherboard, power supply.
- Software: operating system, word processor, web browser, games.
- 硬件：CPU、内存、硬盘、主板、电源。
- 软件：操作系统、文字处理软件、网页浏览器、游戏。
2. Input, Output and Storage Devices | 输入、输出与存储设备
Input devices allow users to enter data into a computer. Common examples include the keyboard, mouse, microphone, touchscreen and scanner. Output devices display or produce results, such as monitors, printers and speakers.
输入设备允许用户将数据输入计算机。常见例子包括键盘、鼠标、麦克风、触摸屏和扫描仪。输出设备显示或生成结果，例如显示器、打印机和扬声器。
Storage devices can be divided into primary storage and secondary storage. Primary storage, such as RAM, is volatile and loses data when power is off. Secondary storage, such as hard disk drives (HDD), solid-state drives (SSD) and USB flash drives, is non-volatile and keeps data permanently.
存储设备可分为主存储器和辅助存储器。主存储器（如内存）是易失性的，断电后数据丢失。辅助存储器（如机械硬盘HDD、固态硬盘SSD和U盘）是非易失性的，可永久保存数据。
| Storage type | Example | Volatile? |
| Primary | RAM | Yes |
| Secondary | HDD, SSD, USB | No |
3. Binary Representation and Data Units | 二进制表示与数据单位
Computers use binary because digital circuits have two stable states: on and off. These states are represented by 1 and 0. A single binary digit is called a bit.
计算机使用二进制，因为数字电路有两种稳定状态：开和关。这两种状态用1和0表示。一个二进制位称为比特（bit）。
Data units are built from bits. A nibble is 4 bits, a byte is 8 bits, and larger units are multiples of bytes. For example, 1 KB is 1024 bytes, 1 MB is 1024 KB, and 1 GB is 1024 MB.
数据单位由比特组成。半字节（nibble）为4位，字节（byte）为8位，更大的单位是字节的倍数。例如，1 KB等于1024字节，1 MB等于1024 KB，1 GB等于1024 MB。
1101₂ = 1×2³ + 1×2² + 0×2¹ + 1×2⁰ = 8 + 4 + 0 + 1 = 13₁₀
To convert binary to denary, write the place values as powers of 2. Then add the values where a 1 appears.
将二进制转换为十进制时，先写出以2为底的权值。然后将出现1的位对应的数值相加。
| Unit | Number of bytes |
| 1 KB | 1024 bytes |
| 1 MB | 1024 KB |
| 1 GB | 1024 MB |
| 1 TB | 1024 GB |
4. Hexadecimal and Character Encoding | 十六进制与字符编码
Hexadecimal is a base-16 number system that uses the digits 0-9 and the letters A-F. It is used as a shorter way to represent binary values. Each hex digit represents exactly 4 bits, so one byte can be written as two hex digits.
十六进制是一种基数为16的数制，使用数字0-9和字母A-F。它用于更简短地表示二进制值。每个十六进制位恰好代表4位，因此一个字节可以写成两个十六进制位。
Character encoding assigns a unique binary code to each character. ASCII uses 7 or 8 bits and can represent English letters, digits and symbols. Unicode uses more bits and can represent characters from almost all writing systems, including Chinese.
字符编码为每个字符分配唯一的二进制代码。ASCII使用7或8位，可以表示英文字母、数字和符号。Unicode使用更多位，可以表示几乎所有书写系统的字符，包括中文。
1011 1101₂ = BD₁₆
To convert a byte to hexadecimal, split the binary number into two nibbles. Convert each nibble into its hex digit, which gives a compact representation.
将一个字节转换为十六进制时，将二进制数分成两个半字节。将每个半字节转换为对应的十六进制位，即可得到紧凑的表示。
5. Introduction to Python Programming | Python编程入门
Python is a high-level programming language that is popular in schools because its syntax is simple and readable. Programs are written as text files and executed by the Python interpreter.
Python是一种高级编程语言，因其语法简单易懂而在学校中广受欢迎。程序以文本文件形式编写，并由Python解释器执行。
The print() function displays output on the screen, while the input() function reads text entered by the user. Comments start with the hash symbol # and are ignored by the computer.
print()函数在屏幕上显示输出，而input()函数读取用户输入的文本。注释以井号#开头，计算机会忽略它们。
print(“Hello, world!”)
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