📚 Hardware | 硬件
Hardware refers to the physical components of a computer system that you can see and touch. In the Cambridge IGCSE Computer Science syllabus, understanding hardware is essential because every program, sensor reading, and output depends on these electronic parts working together.
硬件是指计算机系统中可以看得见、摸得着的物理部件。在剑桥 IGCSE 计算机科学课程中，理解硬件至关重要，因为每一个程序、传感器读数和输出都依赖这些电子部件协同工作。
1. What Is Hardware? | 什么是硬件？
Hardware includes all the physical parts of a computer, such as the processor, memory, storage drives, keyboard, monitor, and internal circuit boards. It is distinct from software, which is the set of instructions that tells the hardware what to do.
硬件包括计算机的所有物理部件，例如处理器、存储器、存储驱动器、键盘、显示器和内部电路板。它与软件不同，软件是指告诉硬件该做什么的一组指令。
Hardware can be divided into internal components and external peripherals. Internal components are usually fitted inside the system unit, while peripherals connect externally through ports or wireless links.
硬件可以分为内部组件和外部外设。内部组件通常安装在主机箱内，而外设通过端口或无线连接在外部连接。
2. The CPU: Control and Processing | 中央处理器：控制与处理
The central processing unit (CPU) is often called the 'brain' of the computer. It carries out instructions from programs by performing the fetch–decode–execute cycle.
中央处理器（CPU）通常被称为计算机的 "大脑"。它通过执行取指–译码–执行周期来运行程序中的指令。
Key parts of the CPU include the control unit (CU), the arithmetic logic unit (ALU), and registers. The CU directs data flow, the ALU performs calculations and logic operations, and registers are very fast temporary storage locations.
CPU 的关键部件包括控制单元（CU）、算术逻辑单元（ALU）和寄存器。控制单元指挥数据流，算术逻辑单元执行计算和逻辑运算，寄存器是非常快速的临时存储位置。
The clock speed, number of cores, and cache size affect CPU performance. Clock speed is measured in hertz (Hz), and modern processors often run at several gigahertz (GHz).
时钟速度、核心数量和缓存大小会影响 CPU 性能。时钟速度以赫兹（Hz）为单位，现代处理器通常运行在几吉赫兹（GHz）。
Performance ≈ Clock speed × Cores × Cache efficiency
3. Primary Memory: RAM and ROM | 主存储器：RAM 与 ROM
Primary memory is directly accessed by the CPU. The two main types are random access memory (RAM) and read-only memory (ROM).
主存储器由 CPU 直接访问。两种主要类型是随机存取存储器（RAM）和只读存储器（ROM）。
RAM is volatile, meaning it loses all data when the power is turned off. It stores the operating system, programs, and data currently in use, allowing fast read and write operations.
RAM 是易失性的，也就是说断电后所有数据都会丢失。它存储当前正在使用的操作系统、程序和数据，支持快速读写操作。
ROM is non-volatile and typically stores the boot program (BIOS or firmware) that starts the computer. The contents of ROM are usually written during manufacture and cannot be changed easily.
ROM 是非易失性的，通常存储启动计算机的引导程序（BIOS 或固件）。ROM 的内容通常在制造时写入，不易更改。
| Feature | RAM | ROM |
| Volatility | Volatile | Non-volatile |
| Typical use | Running programs and data | Boot instructions |
| Read/write | Read and write | Mostly read only |
4. Secondary Storage Devices | 辅助存储设备
Secondary storage provides non-volatile, long-term storage for data and programs. Examples include hard disk drives (HDDs), solid-state drives (SSDs), USB flash drives, CDs, and DVDs.
辅助存储为非易失性的长期数据与程序存储。例子包括硬盘驱动器（HDD）、固态驱动器（SSD）、U盘、CD 和 DVD。
HDDs use spinning magnetic disks and read/write heads, offering large capacity at low cost but with moving parts that can fail or be slow. SSDs use flash memory with no moving parts, making them faster and more durable but often more expensive per gigabyte.
HDD 使用旋转的磁盘和读写磁头，容量大、成本低，但有移动部件，可能损坏或速度较慢。SSD 使用闪存，没有移动部件，因此更快、更耐用，但每 GB 价格通常更高。
Optical storage such as CDs, DVDs, and Blu-ray discs is read by lasers. These discs are portable and cheap but have lower capacity than modern magnetic or solid-state drives.
CD、DVD 和蓝光光盘等光存储由激光读取。这些光盘便携、便宜，但容量低于现代磁性或固态驱动器。
5. Input Devices | 输入设备
Input devices allow users to enter data or commands into a computer. Common examples include keyboards, mice, microphones, scanners, cameras, and touch screens.
输入设备允许用户将数据或命令输入计算机。常见的例子包括键盘、鼠标、麦克风、扫描仪、摄像头和触摸屏。
Sensors are important input devices in scientific and control systems. They measure physical quantities such as temperature, light, pressure, or humidity and convert them into electrical signals for the computer.
传感器是科学和控制系统中的重要输入设备。它们测量温度、光、压力或湿度等物理量，并将其转换为计算机可处理的电信号。
For example, a temperature sensor in a greenhouse can send readings to a computer. If the temperature rises above a set level, the computer may switch on a fan or open a window automatically.
例如，温室中的温度传感器可以将读数发送到计算机。如果温度升高到设定值以上，计算机可能自动打开风扇或窗户。
6. Output Devices | 输出设备
Output devices communicate results from the computer to the user or to another system. Common output devices include monitors, printers, speakers, and projectors.
输出设备将计算机的结果传达给用户或另一个系统。常见的输出设备包括显示器、打印机、扬声器和投影仪。
Actuators are output devices used in control systems. They convert electrical signals from the computer into physical movement or action, such as turning on a motor, opening a valve, or sounding a buzzer.
执行器是控制系统中使用的输出设备。它们将来自计算机的电信号转换为物理运动或动作，例如启动电机、打开阀门或鸣响蜂鸣器。
An output device such as an LED can show status, while a speaker can produce sound. The choice of output device depends on the data and the user's needs.
诸如 LED 之类的输出设备可以显示状态，而扬声器可以产生声音。输出设备的选择取决于数据和用户需求。
7. The Motherboard and System Bus | 主板与系统总线
The motherboard is the main circuit board that connects the CPU, memory, storage, and expansion cards. It provides the pathways through which data and control signals travel.
主板是连接 CPU、内存、存储和扩展卡的主电路板。它提供数据和控制信号传输的通路。
A system bus is a set of parallel wires or tracks divided into three types: the data bus, the address bus, and the control bus. The data bus carries data, the address bus identifies memory locations, and the control bus sends timing and control signals.
系统总线是一组并行导线或走线，分为三种类型：数据总线、地址总线和控制总线。数据总线传输数据，地址总线标识内存位置，控制总线发送时序和控制信号。
Bus width matters because a wider data bus can transfer more bits at once, improving performance. For example, a 64-bit data bus can move 64 bits in one clock cycle.
总线宽度很重要，因为更宽的数据总线一次可以传输更多位，从而提高性能。例如，64 位数据总线可以在一个时钟周期内传送 64 位。
8. Embedded Systems | 嵌入式系统
An embedded system is a computer system designed for a specific function within a larger device, such as a washing machine, microwave oven, digital camera, or car engine controller.
嵌入式系统是设计用于较大设备中特定功能的计算机系统，例如洗衣机、微波炉、数码相机或汽车发动机控制器。
Embedded systems usually contain a microcontroller or microprocessor, memory, and input/output interfaces on a single chip. They are often low-cost, low-power, and very reliable because they carry out only a limited set of tasks.
嵌入式系统通常在一个芯片上包含微控制器或微处理器、存储器和输入/输出接口。它们通常成本低、功耗低且非常可靠，因为它们只执行一组有限的任务。
Examples of inputs and outputs in embedded systems include buttons, sensors, displays, motors, and LEDs. The program is often stored in ROM or flash memory.
嵌入式系统中的输入和输出示例包括按钮、传感器、显示器、电机和 LED。程序通常存储在 ROM 或闪存中。
9. Logic Gates as Hardware Building Blocks
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