📚 Computer Systems | 计算机系统
A computer system is a combination of hardware and software that works together to process data. In Cambridge IGCSE Computer Science, understanding computer systems means knowing the function of each component, how data flows between them, and how the CPU executes instructions.
计算机系统是由硬件和软件共同组成的，用于处理数据的整体。在剑桥 IGCSE 计算机科学课程中，理解计算机系统意味着要了解每个组件的功能、数据如何在组件之间流动，以及 CPU 如何执行指令。
1. What is a Computer System? | 什么是计算机系统？
e output. The basic model is input → process → output, with storage supporting each stage.
计算机系统由硬件、软件和数据共同组成，它们协同完成输入、处理、存储和输出。基本模型是输入 → 处理 → 输出，存储则支持各个阶段。
Hardware refers to the physical parts you can touch, such as the processor, memory, keyboard, and monitor. Software is the set of instructions that tells the hardware what to do.
硬件是指可以触摸的物理部件，例如处理器、内存、键盘和显示器。软件是告诉硬件如何工作的一组指令。
2. Components of a Computer System | 计算机系统的组成
A typical personal computer contains a motherboard, CPU, RAM, ROM, secondary storage, a power supply, and ports for input and output devices. These components communicate through buses: the address bus, data bus, and control bus.
典型的个人计算机包含主板、CPU、RAM、ROM、辅助存储器、电源以及输入输出设备端口。这些组件通过总线通信：地址总线、数据总线和控制总线。
The motherboard is the main circuit board that connects all components. The system bus carries addresses, data, and control signals between the CPU, memory, and input/output controllers.
主板是连接所有部件的主电路板。系统总线在 CPU、内存和输入输出控制器之间传送地址、数据和控制信号。
3. Input Devices | 输入设备
Input devices convert real-world data into a form the computer can process. Common examples include the keyboard, mouse, microphone, scanner, barcode reader, sensor, and touch screen.
输入设备将现实世界的数据转换成计算机能够处理的形式。常见例子有键盘、鼠标、麦克风、扫描仪、条形码阅读器、传感器和触摸屏。
A barcode reader uses a laser or camera to read the pattern of black and white bars, converting it into a product code. Sensors measure physical quantities such as temperature, light, pressure, or motion and send digital signals to the computer.
条形码阅读器使用激光或摄像头读取黑白条纹图案，将其转换为商品编码。传感器测量温度、光线、压力或运动等物理量，并将数字信号发送给计算机。
4. Output Devices | 输出设备
Output devices convert processed data back into a human-readable or machine-usable form. Monitors, printers, speakers, projectors, and actuators are common examples.
输出设备将处理后的数据转换回人类可读或机器可用的形式。显示器、打印机、扬声器、投影仪和致动器是常见例子。
An inkjet printer sprays tiny droplets of ink onto paper, making it suitable for high-quality colour photos. A laser printer uses toner and static electricity, which is faster and cheaper per page for high-volume text printing.
喷墨打印机将微小墨滴喷到纸上，适合高质量彩色照片。激光打印机使用碳粉和静电，对于大量文本打印来说速度更快、单页成本更低。
5. Primary Memory: RAM and ROM | 主存储器：RAM 和 ROM
Primary memory is directly accessed by the CPU and includes RAM and ROM. RAM is volatile, meaning it loses its contents when power is switched off, while ROM is non-volatile and retains data permanently.
主存储器由 CPU 直接访问，包括 RAM 和 ROM。RAM 是易失性的，断电后内容会丢失；而 ROM 是非易失性的，能够永久保存数据。
RAM stores the operating system, running programs, and data currently in use. ROM stores the bootstrap loader or BIOS firmware, which starts the computer when it is switched on.
RAM 存储操作系统、正在运行的程序和当前使用的数据。ROM 存储引导加载程序或 BIOS 固件，用于开机时启动计算机。
| Feature | RAM | ROM |
| Volatility | Volatile | Non-volatile |
| Main use | Running programs and data | Boot instructions and firmware |
RAM 和 ROM 的主要区别在于易失性：断电时 RAM 清空，ROM 保留内容。RAM 用于临时存储，ROM 用于固定的启动指令。
6. Secondary Storage | 辅助存储器
Secondary storage is non-volatile and used for long-term data retention. Magnetic hard disk drives, solid-state drives, optical discs, and USB flash drives are common types.
辅助存储器是非易失性的，用于长期保存数据。常见类型有磁性硬盘驱动器、固态硬盘、光盘和 USB 闪存盘。
HDDs use spinning magnetic platters and read/write heads; they offer large capacity at low cost but are slower and easily damaged by movement. SSDs use flash memory with no moving parts, making them faster, quieter, and more durable but usually more expensive per gigabyte.
HDD 使用旋转的磁性盘片和读写头；它们容量大、成本低，但速度较慢且容易因震动损坏。SSD 使用闪存，没有移动部件，因此更快、更安静、更耐用，但每 GB 价格通常更高。
7. The Central Processing Unit (CPU) | 中央处理器（CPU）
The CPU is the brain of the computer. It executes instructions and controls data flow. Its main parts are the control unit, arithmetic logic unit, registers, and cache.
CPU 是计算机的大脑。它执行指令并控制数据流动。主要部件包括控制单元、算术逻辑单元、寄存器和高速缓存。
The control unit (CU) decodes instructions and sends control signals. The arithmetic logic unit (ALU) performs calculations and logical comparisons. Registers are very fast, small storage locations inside the CPU, such as the program counter and accumulator.
控制单元（CU）对指令进行译码并发送控制信号。算术逻辑单元（ALU）执行算术运算和逻辑比较。寄存器是 CPU 内部极快的小型存储位置，例如程序计数器和累加器。
8. The Fetch-Decode-Execute Cycle | 取指-译码-执行周期
The CPU repeatedly follows the fetch-decode-execute cycle. In the fetch stage, the address in the program counter is copied to the memory address register, an instruction is fetched from RAM into the memory data register, and the program counter is incremented.
CPU 不断重复取指-译码-执行周期。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，指令从 RAM 取入存储器数据寄存器，程序计数器加一。
In the decode stage, the control unit interprets the instruction. In the execute stage, the appropriate part of the CPU, such as the ALU, carries out the operation. The result may be stored in a register or memory.
在译码阶段，控制单元解释指令。在执行阶段，CPU 的相关部件（如 ALU）执行操作。结果可能存入寄存器或内存。
9. Embedded Systems | 嵌入式系统
An embedded system is a computer system built into a larger device to perform a dedicated function. Examples include washing machines, microwave ovens, digital cameras, car engine control units, and medical monitors.
嵌入式系统是嵌入在较大设备中、用于执行特定功能的计算机系统。例子包括洗衣机、微波炉、数码相机、汽车发动机控制单元和医疗监护仪。
Embedded systems are often based on microcontrollers and run firmware stored in ROM. They are reliable, low-cost, and energy-efficient because they only run the specific task they were designed for.
嵌入式系统通常基于微控制器，并运行存储在 ROM 中的固件。它们可靠、成本低、能耗小，因为它们只运行设计好的特定任务。
10. Operating Systems | 操作系统
An operating system is system software that manages hardware and software resources. It provides a user interface, memory management, process management, file management, device drivers, and security.
操作系统是管理硬件和软件资源的系统软件。它提供用户界面、内存管理、进程管理、文件管理、设备驱动和安全功能。
Examples include Microsoft Windows, macOS, Linux, iOS, and Android. Utility software, such as antivirus, backup, compression, and disk defragmentation tools, helps maintain the system.
例子包括 Microsoft Windows、macOS、Linux、iOS 和 Android。实用软件（如杀毒、备份、压缩和磁盘碎片整理工具）帮助维护系统。
11. System Performance and Cache | 系统性能与缓存
CPU performance is affected by clock speed, number of cores, cache size, and instruction set. A higher clock speed means more cycles per second, measured in hertz. More cores allow more instructions to be processed at the same time.
CPU 性能受时钟频率、核心数量、缓存大小和指令集影响。时钟频率越高，每秒执行的周期越多，单位是赫兹。核心越多，可以同时处理更多指令。
Cache is a small amount of very fast memory inside or near the CPU. It stores frequently used instructions and data, reducing the need to access slower RAM and therefore improving overall speed.
缓存是 CPU 内部或附近的一小块极快存储器。它保存经常使用的指令和数据，减少访问较慢 RAM 的次数，从而提高整体速度。
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