📚 IGCSE WJEC Computer Science: Essential Concept Comparisons | IGCSE WJEC 计算机：核心知识点对比
Understanding IGCSE WJEC Computer Science means more than just memorising definitions — it's about seeing how key ideas relate and differ. This guide walks you through the most important concept comparisons, from hardware versus software to symmetric and asymmetric encryption. For each pair, concise English explanations are immediately followed by Chinese translations, helping you build clear, exam-ready knowledge for the WJEC specification.
理解 IGCSE WJEC 计算机科学不仅仅是背诵定义，更在于看清核心概念之间的联系与区别。本指南将带你梳理最重要的知识点对比，从硬件与软件到对称与非对称加密。每一对概念都会先用英文简明解释，紧接着给出中文翻译，帮助你建立清晰、适合 WJEC 考试的知识体系。
1. Hardware vs Software | 硬件与软件
Hardware refers to any physical component of a computer system that you can touch, such as the processor, RAM, hard disk drive, keyboard, and monitor.
硬件指计算机系统中任何可以触摸的物理部件，例如处理器、内存、硬盘、键盘和显示器。
Software is the collection of programs and instructions that tell the hardware how to perform tasks. It is intangible and stored digitally.
软件是告诉硬件如何执行任务的程序和指令的集合。它是无形的，以数字形式存储。
Hardware provides the actual machinery that executes operations, while software provides the logic and data. Neither can function usefully without the other.
硬件提供执行操作的实际机械装置，而软件提供逻辑和数据。二者缺一不可，否则都无法发挥有效作用。
Examples of hardware include motherboards, graphics cards, and USB flash drives; examples of software include operating systems, word processors, and games.
硬件的例子有主板、显卡和 U 盘；软件的例子有操作系统、文字处理软件和游戏。
2. Input vs Output Devices | 输入与输出设备
An input device sends data or control signals into a computer system, allowing users to communicate with the machine. Common examples are keyboards, mice, touchscreens, and microphones.
输入设备将数据或控制信号送入计算机系统，让用户能够与机器交互。常见的例子有键盘、鼠标、触摸屏和麦克风。
An output device receives data from the computer and presents it to the user in a meaningful form, such as a monitor displaying images or a speaker playing sound.
输出设备接收来自计算机的数据，并以有意义的形式呈现给用户，例如显示器显示图像或扬声器播放声音。
Some devices function as both input and output, like a touchscreen that accepts touch input and simultaneously displays visual output.
有些设备兼具输入和输出功能，例如触摸屏既能接受触摸输入，同时又能显示视觉输出。
The key distinction lies in the direction of data flow: into the computer (input) or out of the computer (output).
主要区别在于数据流的方向：进入计算机（输入）还是从计算机发出（输出）。
3. Primary vs Secondary Storage | 主存储器与辅助存储器
Primary storage, such as RAM and cache, is directly accessible by the CPU and typically volatile, meaning it loses its contents when the power is turned off.
主存储器（如 RAM 和缓存）可由 CPU 直接访问，且通常是易失性的，即断电后内容会丢失。
Secondary storage includes devices like hard disks, solid-state drives, and optical discs. These hold data permanently (non-volatile) and have much larger capacities, but they are slower to access than primary storage.
辅助存储器包括硬盘、固态硬盘和光盘等设备。它们能永久保存数据（非易失性），容量也大得多，但访问速度比主存储器慢。
Primary storage is used for instructions and data currently being processed; secondary storage is used for long-term data retention, including the operating system, applications, and user files.
主存储器用于存放当前正在处理的指令和数据；辅助存储器用于长期保存数据，包括操作系统、应用程序和用户文件。
When a computer is running, it frequently moves data between primary and secondary storage to ensure the CPU has fast access to what it needs.
计算机运行时，会频繁地在主存储器和辅助存储器之间移动数据，以确保 CPU 能够快速获取所需内容。
4. RAM vs ROM | 随机存取存储器与只读存储器
RAM (Random Access Memory) is volatile memory that temporarily holds the operating system, application programs, and data in current use. Its contents are lost when the power is switched off.
RAM（随机存取存储器）是易失性存储器，临时存放操作系统、应用程序和当前使用的数据。一旦断电，其内容便会丢失。
ROM (Read-Only Memory) is non-volatile and retains its data even when the computer is off. It stores firmware, such as the BIOS, which is essential for booting the computer.
ROM（只读存储器）是非易失性的，断电后仍能保留数据。它存储固件，例如启动计算机所必需的 BIOS。
RAM can be read from and written to repeatedly, making it ideal for active task execution. ROM is primarily read-only during normal operation, though some types can be updated with special procedures.
RAM 可以反复读取和写入，非常适合执行当前任务。ROM 在正常操作下主要是只读的，尽管某些类型可通过特殊流程进行更新。
The size of RAM directly impacts multitasking performance, whereas ROM size is usually fixed and relatively small compared to RAM.
RAM 的大小直接影响多任务处理性能，而 ROM 的容量通常固定，且相比于 RAM 要小得多。
5. System Software vs Application Software | 系统软件与应用软件
System software manages and controls the hardware so that other software can function. The most important example is the operating system (e.g., Windows, macOS, Linux), which handles memory management, file systems, and device drivers.
系统软件负责管理和控制硬件，使其他软件能够运行。最重要的例子是操作系统（如 Windows、macOS、Linux），它处理内存管理、文件系统和设备驱动等工作。
Application software performs specific tasks for the user, such as word processing, web browsing, or photo editing. It relies on the services provided by system software to operate.
应用软件为用户执行特定任务，例如文字处理、网页浏览或照片编辑。它依赖系统软件提供的服务才能运行。
System software runs in the background and often starts automatically when the computer boots, whereas application software is launched by the user when needed.
系统软件在后台运行，通常在计算机启动时自动运行；而应用软件则由用户在需要时启动。
Utility programs like antivirus software or disk defragmenters are a subclass of system software designed to maintain and protect the computer.
像杀毒软件或磁盘碎片整理程序这样的实用程序是系统软件的一个子类，旨在维护和保护计算机。
6. High-Level vs Low-Level Languages | 高级语言与低级语言
High-level languages (HLLs) such as Python, Java, and C# use English-like syntax and abstract away hardware details. They are easy to read, write, and debug for humans.
高级语言（如 Python、Java 和 C#）使用类似英语的语法，并隐藏了硬件细节。它们易于人类阅读、编写和调试。
Low-level languages include machine code (binary) and assembly language. They are closely tied to the processor's instruction set and give the programmer precise control over hardware.
低级语言包括机器码（二进制）和汇编语言。它们与处理器的指令集密切相关，使程序员能够精确控制硬件。
HLL programs must be translated into machine code by compilers or interpreters, whereas assembly language is converted using an assembler.
高级语言程序必须由编译器或解释器转换为机器码，而汇编语言则通过汇编器进行转换。
Portability is a major advantage of HLLs: the same source code can run on different hardware with minimal changes. Low-level code is usually specific to one type of processor.
可移植性是高级语言的一大优势：相同的源代码只需少量修改即可在不同硬件上运行。低级代码通常只适用于某一类处理器。
7. Compiler vs Interpreter | 编译器与解释器
A compiler translates the entire high-level source code into machine code in one go, producing a standalone executable file. Once compiled, the program can be run multiple times without further translation.
编译器一次性将整个高级语言源代码翻译为机器码，生成一个独立的可执行文件。程序一旦编译完成，就可以多次运行而无需再次翻译。
An interpreter translates and executes high-level code line by line, without generating a separate machine-code file. This means the source code must be present each time the program runs.
解释器逐行翻译并执行高级语言代码，不生成独立的机器码文件。这意味着每次运行程序时都必须提供源代码。
Compiled programs generally run faster because the translation is done beforehand. Interpreted programs are usually slower at runtime but can be easier to debug since errors are reported immediately at the line causing the problem.
编译后的程序通常运行速度更快，因为翻译已提前完成。解释型程序在运行时通常较慢，但调试可能更容易，因为出错时会立即报告问题所在行。
Languages like C++ and Go are typically compiled; Python and JavaScript are often interpreted, although modern environments may use just-in-time (JIT) compilation to improve performance.
像 C++ 和 Go 这样的语言通常是编译型的；Python 和 JavaScript 常常采用解释方式，但现代环境可能会使用即时编译（JIT）来提高性能。
8. LAN vs WAN | 局域网与广域网
A Local Area Network (LAN) connects computers and devices within a small geographical area, such as a school, office building, or home. LANs typically offer high data transfer speeds and low latency.
局域网（LAN）连接较小地理范围（如学校、办公楼或家庭）内的计算机和设备。局域网通常提供高速数据传输和低延迟。
A Wide Area Network (WAN) spans a large geographical area, often connecting multiple LANs across cities, countries, or continents. The internet is the largest example of a WAN.
广域网（WAN）覆盖广阔的地理区域，常常将分布于不同城市、国家甚至大洲的多个局域网连接起来。互联网就是最大的广域网。
LANs are usually owned, controlled, and maintained by a single organisation, whereas WAN infrastructure is provided by telecommunications companies and may involve leased lines or satellite links.
局域网通常由单一组织拥有、控制和维护，而广域网的基础设施由电信公司提供，可能涉及租用线路或卫星连接。
Data transfer speeds on a LAN (e.g., 1 Gbps or faster) are typically much higher than on a WAN, where speeds can be affected by distance and network congestion.
局域网的数据传输速度（例如 1 Gbps 或更高）通常远高于广域网，后者的速度可能受距离和网络拥塞的影响。
9. TCP vs UDP | TCP 与 UDP
Transmission Control Protocol (TCP) is a connection-oriented protocol that ensures reliable data delivery. It establishes a connection, numbers packets, and requests retransmission if any packet is lost, guaranteeing that data arrives complete and in order.
传输控制协议（TCP）是一种面向连接的协议，可确保可靠的数据传输。它建立连接、为数据包编号，若有数据包丢失则请求重传，从而保证数据完整且按序到达。
User Datagram Protocol (UDP) is a connectionless protocol that sends packets without establishing a connection or checking whether they are received. This makes it faster but less reliable than TCP.
用户数据报协议（UDP）是一种无连接协议，发送数据包前不建立连接，也不检查对方是否收到。这使其速度更快，但可靠性不如 TCP。
TCP is used where accuracy is critical, such as loading web pages, sending emails, or transferring files. UDP is preferred for real-time applications like video streaming, online gaming, and VoIP, where occasional data loss is acceptable if it reduces latency.
TCP 用于对准确性要求极高的场景，如加载网页、发送电子邮件或传输文件。UDP 则更适合实时应用，如视频流、在线游戏和网络电话，在这些场景中偶尔的数据丢失是可以接受的，只要减少延迟即可。
TCP includes flow control and congestion avoidance mechanisms, which add overhead. UDP has minimal overhead, making it lightweight and efficient for broadcasting or multicasting.
TCP 包含流量控制和拥塞避免机制，这会增加额外开销。UDP 的开销极小，因此轻量高效，适合广播或多播。
10. Symmetric vs Asymmetric Encryption | 对称与非对称加密
Symmetric encryption uses a single secret key for both encrypting and decrypting data. Both the sender and the receiver must share this key securely beforehand.
对称加密使用同一个秘密密钥进行数据的加密和解密。发送方和接收方必须事先通过安全方式共享该密钥。
Asymmetric encryption, also called public-key cryptography, involves a pair of keys: a public key (which can be shared openly) and a private key (kept secret). Data encrypted with the public key can only be decrypted by the matching private key, and vice versa.
非对称加密，也称为公钥加密，使用一对密钥：公钥（可公开分享）和私钥（保密）。用公钥加密的数据只能用对应的私钥解密，反之亦然。
Symmetric encryption is generally much faster and is often used for encrypting large volumes of data, such as in secure file storage or bulk data transfer.
对称加密通常要快得多，常用于加密大量数据，如安全文件存储或批量数据传输。
Asymmetric encryption provides a solution to the key distribution problem and is essential for establishing secure connections on the internet (e.g., SSL/TLS certificates). However, it is computationally more expensive than symmetric encryption.
非对称加密解决了密钥分发问题，对于建立互联网安全连接（例如 SSL/TLS 证书）至关重要。但它的计算开销比对称加密更大。
11. Lossy vs Lossless Compression | 有损与无损压缩
Lossless compression reduces file size without removing any information. The original data can be perfectly reconstructed from the compressed file. This is essential for text documents, executable files, and spreadsheet data where every bit matters.
无损压缩在不丢失任何信息的前提下减小文件大小。原始数据可以从压缩文件中完美还原。这对于文本文档、可执行文件和电子表格数据至关重要，因为每一个比特都很重要。
Lossy compression achieves much smaller file sizes by permanently discarding some data that are less noticeable to human senses. For instance, it may remove audio frequencies outside the range of hearing or simplify subtle colour variations in an image.
有损压缩通过永久丢弃一些人类感官不易察觉的数据，实现更小的文件体积。例如，它可能移除听力范围外的音频频率，或简化图像中细微的颜色变化。
Typical lossless formats include PNG for images, FLAC for audio, and ZIP for general files. Common lossy formats are JPEG for photos, MP3 for music, and MP4 (video) with specific codecs.
典型的无损格式包括用于图像的 PNG、用于音频的 FLAC，以及用于一般文件的 ZIP。常见的有损格式有用于照片的 JPEG、用于音乐的 MP3，以及采用特定编码器的 MP4（视频）。
The choice between lossy and lossless compression involves a trade-off: preserving perfect quality versus maximising storage or bandwidth savings.
选择有损还是无损压缩需要权衡：是保留完美品质，还是最大化节省存储空间或带宽。
12. Ethics vs Legal Issues in Computing | 计算机领域的道德与法律问题
Ethics in computing refers to moral principles that guide acceptable behaviour, such as respecting user privacy, avoiding biased algorithms, and using artificial intelligence responsibly. These are often not enforced by law but are expected by society.
计算机领域的道德是指指导可接受行为的道德准则，例如尊重用户隐私、避免有偏见的算法，以及负责任地使用人工智能。这些通常没有法律强制力，但社会期望如此。
Legal issues are rules established by legislation that must be followed, such as the Data Protection Act, Computer Misuse Act, and Copyright, Designs and Patents Act. Violating these laws can lead to prosecution.
法律问题是由立法确立的必须遵守的规则，例如《数据保护法》《计算机滥用法》以及《版权、设计和专利法》。违反这些法律可能会导致起诉。
An action may be legal but unethical — for example, a company might lawfully collect huge amounts of personal data but use it in ways that manipulate consumers without clearly informing them.
某种行为可能合法但不道德——例如，一家公司可能合法收集大量个人数据，但以操纵消费者的方式使用这些数据，却没有明确告知用户。
Professional bodies such as the BCS (The Chartered Institute for IT) publish codes of conduct to bridge the gap between legal requirements and ethical practice, encouraging computing professionals to act with integrity and in the public interest.
像 BCS（英国计算机学会）这样的专业机构发布行为准则，以弥合法律要求与道德实践之间的差距，鼓励计算机专业人士诚信行事并维护公众利益。
Published by TutorHao | Computer Science Revision Series | aleveler.com
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