📚 Computer Hardware: Architecture, Devices, Storage & Networks | 计算机硬件：架构、设备、存储与网络
Computer hardware forms the physical foundation of every computing system. For CIE Computer Science, understanding the internal architecture, peripheral devices, storage hierarchy, and networking fundamentals is essential for both theoretical exams and practical application.
计算机硬件是每一个计算系统的物理基础。对于 CIE 计算机科学而言，理解内部架构、外围设备、存储层次结构以及网络基础知识，对理论考试和实际应用都至关重要。
1. Von Neumann Architecture | 冯·诺依曼架构
The Von Neumann architecture describes a stored-program computer where instructions and data share the same memory space, accessed via a single bus system. The central processing unit (CPU) fetches instructions from memory, decodes them, and executes operations sequentially.
冯·诺依曼架构描述了一种存储程序计算机，其中指令和数据共享同一存储空间，并通过单一总线系统访问。中央处理器（CPU）从存储器中取出指令、进行译码，并按顺序执行操作。
The architecture consists of four key components:
该架构包含四个关键组成部分：
- CPU (Central Processing Unit) – the brain that performs calculations and controls other components.
- CPU（中央处理器）——执行计算并控制其他部件的核心。
- Main Memory (RAM) – stores both instructions and data currently in use.
- 主存储器（RAM）——存储当前正在使用的指令和数据。
- Input/Output Devices – allow the system to receive data and present results.
- 输入/输出设备——使系统能够接收数据并输出结果。
- System Bus – carries data, addresses, and control signals between components.
- 系统总线——在组件之间传输数据、地址和控制信号。
2. The Central Processing Unit | 中央处理器
The CPU is composed of several internal units that work together to execute machine code instructions. The three main internal components are the Arithmetic Logic Unit (ALU), the Control Unit (CU), and registers.
CPU 由多个内部单元组成，这些单元协同工作以执行机器代码指令。三大内部组件是算术逻辑单元（ALU）、控制单元（CU）和寄存器。
The ALU performs arithmetic operations such as addition, subtraction, multiplication, and division, as well as logical operations like AND, OR, NOT, and XOR for comparisons.
ALU 执行加、减、乘、除等算术运算，以及 AND、OR、NOT 和 XOR 等用于比较的逻辑运算。
The Control Unit decodes instructions and generates control signals that coordinate the flow of data throughout the system. The Program Counter (PC) holds the memory address of the next instruction to be executed.
控制单元对指令进行译码，并生成协调整个系统数据流动的控制信号。程序计数器（PC）保存下一条待执行指令的内存地址。
3. The Fetch–Execute Cycle | 取指-执行周期
The CPU processes instructions through a repeating cycle: Fetch, Decode, Execute, and Store. Each step is controlled by the Control Unit using the system clock.
CPU 通过一个重复的周期处理指令：取指、译码、执行和存储。每一步都由控制单元依据系统时钟进行控制。
Fetch → Decode → Execute → Store → (repeat)
During the fetch stage, the address in the Program Counter is copied to the Memory Address Register (MAR), the instruction is loaded into the Memory Data Register (MDR), and the PC increments to point to the next instruction.
在取指阶段，程序计数器中的地址被复制到存储器地址寄存器（MAR），指令加载到存储器数据寄存器（MDR），同时 PC 递增以指向下一条指令。
During decode, the Control Unit interprets the instruction and determines which operands are needed. During execute, the ALU performs the required operation, and the result is stored back to memory or a register.
在译码阶段，控制单元解释指令并确定需要的操作数。在执行阶段，ALU 执行所需操作，并将结果存回内存或寄存器中。
4. Input Devices | 输入设备
Input devices convert user data or commands into a form that the computer can process. In CIE Computer Science, you should be able to describe common devices, their uses, and their advantages and disadvantages.
输入设备将用户数据或命令转换为计算机可以处理的形式。在 CIE 计算机科学中，你需要能够描述常见设备、它们的用途及优缺点。
- Keyboard – used for entering text and commands; suited to most desktop tasks.
- 键盘——用于输入文本和命令；适用于大多数桌面任务。
- Mouse / Touchpad – provides pointer-based interaction for GUIs.
- 鼠标/触摸板——为图形用户界面提供基于指针的交互。
- Scanner – digitises printed documents or images using reflected light.
- 扫描仪——利用反射光将打印文档或图像数字化。
- Microphone – captures audio for voice recognition or recording.
- 麦克风——捕获音频，用于语音识别或录音。
- Sensors – collect real-world data such as temperature, pressure, light, or motion.
- 传感器——收集温度、压力、光线或运动等现实世界的数据。
5. Output Devices | 输出设备
Output devices present processed data to the user in a human-readable form. Selecting the correct output device depends on the required output type, speed, quality, and cost.
输出设备以人类可读的形式向用户呈现已处理的数据。选择正确的输出设备取决于所需的输出类型、速度、质量和成本。
- Monitor (LCD/LED) – displays text and graphics; fast and silent but consumes power.
- 显示器（LCD/LED）——显示文本和图形；速度快且无噪音，但消耗电能。
- Printer (Inkjet/Laser) – produces physical copies; laser is faster but more expensive per page for colour.
- 打印机（喷墨/激光）——生成纸质副本；激光打印机速度更快，但彩色打印的单页成本更高。
- Speaker / Headphones – output audio signals for multimedia applications.
- 扬声器/耳机——输出音频信号，用于多媒体应用。
- Actuators – convert electrical signals into physical movement (e.g., in robotic or control systems).
- 执行器——将电信号转换为物理运动（例如用于机器人或控制系统）。
6. Primary Storage: RAM and ROM | 主存储器：RAM 与 ROM
Primary storage is directly accessible by the CPU and includes RAM and ROM. RAM is volatile — it loses its contents when power is removed — while ROM is non-volatile and retains data permanently.
主存储器可被 CPU 直接访问，包括 RAM 和 ROM。RAM 是易失性的——断电时内容丢失；ROM 是非易失性的，可以永久保存数据。
| Feature | 特性 | RAM | ROM |
|---|---|---|
| Volatile | 易失性 | Yes | 是 | No | 否 |
| Read/Write | 读/写 | Read & write | 可读可写 | Read only | 只读 |
| Use | 用途 | Running programs & data | 运行程序和存储数据 | Boot-up firmware (BIOS/UEFI) | 启动固件（BIOS/UEFI） |
Virtual memory is a technique where part of the secondary storage is used as an extension of RAM when physical memory is full, allowing larger programs to run but at a slower speed.
虚拟内存是一种技术，当物理内存不足时，将部分辅存用作 RAM 的扩展，使更大的程序能够运行，但速度较慢。
7. Secondary Storage: Magnetic, Optical, Solid-State | 辅存：磁性、光学、固态
Secondary storage provides non-volatile, long-term data storage. It is slower than primary storage but offers much larger capacity at a lower cost per byte.
辅存提供非易失性的长期数据存储。它比主存储速度慢，但容量大得多且单位字节成本更低。
- Magnetic storage (HDD) – uses a rotating platter and read/write head; high capacity, cheap per GB, but mechanically fragile.
- 磁性存储（HDD）——使用旋转盘片和读写磁头；容量大、每 GB 成本低，但机械结构脆弱。
- Optical storage (CD/DVD/Blu-ray) – uses laser light to read pits and lands on a reflective surface; portable and cheap to produce.
- 光存储（CD/DVD/蓝光）——利用激光读取反射面上的凹槽与平面；便携且生产成本低。
- Solid-state storage (SSD) – uses flash memory with no moving parts; fast access, silent, shock-resistant, but more expensive per GB.
- 固态存储（SSD）——使用闪存，无机械部件；访问快、静音、抗冲击，但每 GB 成本更高。
8. Networks: LAN and WAN | 网络：局域网与广域网
A Local Area Network (LAN) covers a small geographical area, such as a school or office building. A Wide Area Network (WAN) spans a large area, such as a city or country, and is often created by connecting multiple LANs.
局域网（LAN）覆盖较小的地理范围，如学校或办公楼。广域网（WAN）覆盖较大范围，如城市或国家，通常由多个 LAN 互联形成。
Networks can be organised using different topologies — the physical or logical arrangement of devices. Common topologies include star and mesh.
网络可以采用不同的拓扑结构进行组织——即设备的物理或逻辑布局。常见拓扑包括星型与网状。
- Star topology – all devices connect directly to a central switch or hub; easy to manage and troubleshoot, but the central device is a single point of failure.
- 星型拓扑——所有设备直接连接至中央交换机或集线器；易于管理和故障排查，但中央设备是单点故障。
- Mesh topology – devices are interconnected; highly redundant and reliable, but expensive and complex to cable.
- 网状拓扑——设备之间相互连接；冗余度高、可靠性强，但布线和成本复杂且昂贵。
9. Network Hardware | 网络硬件
Several hardware components are required to build a functioning network. Each serves a distinct purpose in data transmission.
构建一个可运行的网络需要多种硬件组件。每一个在数据传输中都具有不同的作用。
- Network Interface Card (NIC) – enables a device to connect to the network, either wired or wireless.
- 网卡（NIC）——使设备能够连接网络，支持有线或无线方式。
- Switch – forwards data frames between devices on the same LAN based on MAC addresses.
- 交换机——根据 MAC 地址在同一 LAN 中的设备之间转发数据帧。
- Router – connects different networks and forwards data packets based on IP addresses.
- 路由器——连接不同网络，并根据 IP 地址转发数据包。
- Wireless Access Point (WAP) – allows wireless devices to join a wired network via Wi-Fi.
- 无线接入点（WAP）——允许无线设备通过 Wi-Fi 接入有线网络。
10. Factors Affecting Network Performance | 影响网络性能的因素
In an exam, you may be asked to identify or justify why a network is slow. Several factors influence network performance.
在考试中，你可能会被要求识别或解释网络速度慢的原因。多种因素会影响网络性能。
- Bandwidth – the maximum data transfer rate of a connection; higher bandwidth allows more data per second.
- 带宽——连接的最大数据传输速率；带宽越高，每秒可传输的数据越多。
- Number of users – heavy traffic causes congestion and slower response times.
- 用户数量——高流量会导致拥塞和响应时间变慢。
- Interference – wireless signals can be disrupted by physical obstructions or electromagnetic noise.
- 干扰——无线信号可能受到物理障碍物或电磁噪声的干扰。
- Latency – the time delay for data to travel from source to destination; affected by distance and routing.
- 延迟——数据从源到目的地传输的时间延迟；受距离和路由影响。
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