IGCSE WJEC Computer Science: Operating Systems | IGCSE WJEC计算机：操作系统

📚 IGCSE WJEC Computer Science: Operating Systems | IGCSE WJEC计算机：操作系统

Every time you turn on a computer, open an app or save a file, a hidden layer of software makes it all possible. That layer is the operating system – the essential interface between hardware, applications and users. For your WJEC IGCSE Computer Science exam you need to know exactly what an operating system does, how it manages resources and why different types exist for different devices.

每次你打开电脑、启动一个应用或保存一个文件，都有一层隐形的软件在背后默默支撑。这一层就是操作系统——硬件、应用程序和用户之间必不可少的接口。为了你的 WJEC IGCSE 计算机科学考试，你必须准确掌握操作系统做什么、如何管理资源，以及为什么不同设备需要不同种类的操作系统。

1. What Is an Operating System? | 什么是操作系统？

An operating system (OS) is a low‑level system software that controls the hardware and provides a platform for application software to run. It acts as a bridge between the physical components and the user or programs, hiding complex hardware details behind a consistent interface. Without an OS, a computer would be little more than a collection of inert electronic circuits.

操作系统是一种底层的系统软件，它控制硬件，并为应用软件提供运行平台。它像是物理部件与用户或程序之间的一座桥梁，将复杂的硬件细节隐藏在一个统一的接口后面。没有操作系统，电脑只不过是一堆静止的电子电路。

The OS is stored in non‑volatile storage (usually an SSD or HDD) and loaded into RAM during the boot process. Once running, it stays in memory and manages everything from keyboard presses to network packets, ensuring that programs do not interfere with each other and that the machine remains stable and responsive.

操作系统存放在非易失性存储器（通常是固态硬盘或机械硬盘）中，在启动过程中被加载到内存里。一旦运行，它就驻留在内存中，管理者从键盘按键到网络数据包的一切，确保各程序互不干扰，整台机器保持稳定并迅速响应。

2. Core Functions of an Operating System | 操作系统的核心功能

WJEC expects you to be familiar with the fundamental jobs an OS performs. These can be summarised as managing memory, processes, files, input/output and user interfaces, as well as providing security and utility services. Together, these functions give the user the illusion that they have the machine all to themselves, even when dozens of background tasks are running.

WJEC 要求你熟悉操作系统完成的基本工作。这些工作可以概括为管理内存、进程、文件、输入输出和用户界面，以及提供安全与实用程序服务。这些功能组合在一起，给用户一种整台机器都在为自己独立服务的错觉，即便后台同时运行着数十个任务。

Memory management – allocating RAM to programs and freeing it when no longer needed.
Process management – deciding which program gets CPU time and for how long.
File management – organising, naming and protecting data on storage devices.
I/O management – handling communication with keyboards, mice, printers and network cards.
User interface – providing a means for humans to interact with the machine.
Security and protection – controlling access and preventing unauthorised actions.

内存管理 – 给程序分配内存，用完后回收。
进程管理 – 决定哪个程序获得 CPU 时间以及多长时间。
文件管理 – 在存储设备上组织、命名和保护数据。
输入输出管理 – 控制与键盘、鼠标、打印机、网卡等设备的通信。
用户界面 – 提供人机交互的途径。
安全与保护 – 控制访问，阻止未授权的操作。

3. User Interfaces: GUI, CLI and Menu‑Based | 用户界面：图形、命令行与菜单式

The OS must present a way for users to give commands and receive feedback. The three main types tested by WJEC are Graphical User Interface (GUI), Command Line Interface (CLI) and menu‑based interfaces. Each has strengths and weaknesses, and the choice often depends on the device and the user’s expertise.

操作系统必须提供一种让用户下达命令并接收反馈的途径。WJEC 考试涉及的三种主要类型是图形用户界面（GUI）、命令行界面（CLI）和菜单式界面。每种都有其优缺点，选择通常取决于设备和用户的专业程度。

Interface	Features	Typical Use
GUI	Windows, icons, menus, pointer (WIMP); visually intuitive; requires more RAM and CPU	Personal computers, smartphones
CLI	Text‑based commands; steep learning curve; very fast for experts; uses fewer resources	Servers, routers, developer tools
Menu‑based	Limited lists of options; simple to use but restrictive	ATMs, ticket machines

A GUI is the most common interface for everyday users. It represents files and actions as visual objects, reducing the need to memorise commands. However, it consumes significant system resources. In contrast, a CLI gives precise control and is typically preferred by system administrators for tasks like batch processing or network diagnostics. Menu‑driven interfaces offer a fixed set of options, ideal for public kiosks where user error must be minimised.

GUI 是日常用户最常见的界面。它用视觉对象表示文件和操作，降低了记忆命令的需求，但会消耗大量系统资源。相反，CLI 提供精确控制，系统管理员在进行批处理或网络诊断时通常更喜欢它。菜单驱动的界面提供固定选项，非常适合公共自助机，能最大限度地减少用户错误。

4. Memory Management | 内存管理

The OS is responsible for organising main memory (RAM) so that multiple programs can reside there without corrupting each other. It keeps track of which parts of memory are in use and which are free, allocating space when a program launches and reclaiming it when the program closes. This prevents memory leaks and fragmentation.

操作系统负责组织主存储器（RAM），让多个程序能同时驻留其中而不相互干扰。它会追踪哪些内存区域已被占用、哪些空闲，当程序启动时分配空间，程序关闭时回收，以此防止内存泄漏和碎片化。

Modern operating systems often use paging to divide physical memory into fixed‑sized blocks called frames, while splitting running programs into pages of the same size. A page table maps each logical page to a physical frame, allowing programs to be loaded into non‑contiguous RAM locations. This eliminates the need for the entire program to sit in one continuous block and makes multitasking more efficient.

现代操作系统常使用分页技术，把物理内存分成固定大小的块（称为“帧”），同时把运行的程序也分成同样大小的页。页表将每一逻辑页映射到物理帧，这样程序可以装入不连续的内存位置，从而避免了整个程序必须占据一整块连续空间，让多任务处理更高效。

Number of frames = Total physical memory ÷ Page size

帧数 = 总物理内存 ÷ 页大小

When RAM runs out, the OS can use a section of the hard drive as virtual memory. Pages that are not currently needed are swapped out to disk, freeing up RAM for active processes. However, excessive swapping leads to disk thrashing, which dramatically slows down the system because hard drives are much slower than RAM.

当内存不足时，操作系统可以把硬盘的一部分当作虚拟内存使用。暂时不需要的页被换出到磁盘，为活跃进程腾出内存空间。但过度的交换会导致磁盘颠簸，从而使系统急剧变慢，因为硬盘的速度远慢于内存。

5. Process Management and Multitasking | 进程管理与多任务

A process is a program in execution. The OS must decide which process runs on the CPU at any given moment. It maintains a ready queue of processes waiting for processor time and uses a scheduler to allocate CPU bursts according to certain rules. The aim is to keep the CPU busy while giving every process a fair share and maintaining quick response times for user interactions.

进程是正在运行的程序。操作系统必须决定哪一个进程在任一时刻获得 CPU 使用权。它维护着一个就绪队列，里面是等待处理器时间的进程，并使用调度器按规则分配 CPU 时间片。目标是让 CPU 保持忙碌，给予每个进程公平的份额，同时保证用户交互的快速响应。

There are two key types of multitasking: cooperative and pre‑emptive. In cooperative multitasking, a running program voluntarily releases the CPU; this was used in early desktop operating systems but was risky because a single misbehaving program could halt the whole machine. Modern OS use pre‑emptive multitasking, where the OS forcibly interrupts a process after a fixed time slice, ensuring that no single task monopolises the processor. The context switch – saving the state of the current process and loading the state of the next – happens so quickly that the user sees seamless parallelism.

多任务有两种关键类型：协作式和抢占式。协作式多任务需要运行的程序主动让出 CPU，早期桌面操作系统曾用过这种方式，但风险很大，因为一个出错的程序就能让整台机器停止。现代操作系统采用抢占式多任务，操作系统会在固定时间片后强制中断当前进程，从而确保没有单一任务可以独占处理器。上下文切换——保存当前进程的状态并加载下一个进程的状态——发生得非常快，以致用户看到的仿佛是完美并行的。

CPU time per process ≈ Time slice × (1 / Number of ready processes)

每进程 CPU 时间 ≈ 时间片 × (1 / 就绪进程数量)

6. File Management | 文件管理

The file management system organises data on storage media so that users and applications can store, retrieve and modify information efficiently. The OS creates a hierarchical directory structure (folders) and maintains metadata such as file name, size, type, location and access rights. Files are stored in blocks on a disk, and a file allocation table (FAT) or equivalent index keeps track of which blocks belong to which file.

文件管理系统负责在存储介质上组织数据，让用户和应用能高效地保存、检索和修改信息。操作系统创建层次化的目录结构（文件夹），并维护文件名、大小、类型、位置和访问权限等元数据。文件以块的形式存储在磁盘上，而文件分配表（FAT）或类似的索引会记录哪些块属于哪个文件。

Common operations include creating, deleting, opening, closing, reading, writing and renaming files. The OS also handles access controls, ensuring that only authorised users can read or modify certain files, and manages file locks to prevent conflicts when two users try to edit the same document simultaneously on a network.

常见操作包括创建、删除、打开、关闭、读、写和重命名文件。操作系统还处理访问控制，确保只有授权用户才能读取或修改特定文件，并管理文件锁，以防止网络上两个用户同时编辑同一个文档时发生冲突。

File extensions (e.g., .txt, .jpg, .exe) help the OS identify which application should be used to open a file by default. However, the extension is simply part of the file name and does not guarantee the file’s actual content; security tools often inspect file headers for more reliable identification.

文件扩展名（如 .txt、.jpg、.exe）帮助操作系统识别默认用哪个应用程序打开文件。但扩展名只是文件名的一部分，并不能保证文件的实际内容；安全工具通常会检查文件头以获取更可靠的识别。

7. Input and Output Management | 输入输出管理

Peripheral devices operate at different speeds and use different data formats, so the OS employs device drivers to translate generic I/O requests into device‑specific commands. The driver provides a uniform interface: an application simply issues a print command, and the OS and driver work together to format the document for the specific printer model connected to the computer.

外围设备以不同速度运行，使用不同的数据格式，因此操作系统使用设备驱动程序将通用的输入输出请求转换成特定于设备的命令。驱动程序提供了一个统一接口：应用程序只需发出打印命令，操作系统和驱动程序就会一起将文档格式化成适合连接的具体打印机型号的形式。

Buffering and spooling are two essential techniques. A buffer is a temporary memory area that stores data while it is being transferred between two devices (e.g., keyboard buffer holds keystrokes until the CPU is ready to process them). Spooling stores the entire data stream on a fast medium like a hard drive before sending it to a slower device; a print spooler queues multiple documents, letting the user continue working while the printer slowly handles each job.

缓冲和假脱机是两项关键技术。缓冲是临时存储区，存放两个设备之间正在传输的数据（例如，键盘缓冲会在 CPU 准备好处理之前保存击键）。假脱机则把整个数据流先存储在硬盘等快速介质上，再发送给慢速设备；打印假脱机程序将多个文档排成队列，让用户可以继续工作，而打印机则慢条斯理地处理每个任务。

8. Utility Software and System Security | 实用软件与系统安全

While the OS kernel provides core services, a full operating system includes utility programs that keep the computer running efficiently. Examples include disk defragmentation, backup, compression, encryption and antivirus tools. Defragmentation rearranges fragmented files into contiguous blocks, which speeds up access on mechanical hard drives (but is unnecessary for SSDs). Encryption utilities scramble data so that it can only be read with the correct key.

虽然操作系统内核提供核心服务，但一个完整的操作系统还包含让计算机高效运行的实用程序。例如磁盘碎片整理、备份、压缩、加密和防病毒工具。碎片整理将零散的文件重新排列成连续的块，从而加快机械硬盘的访问速度（但对固态硬盘无必要）。加密工具则把数据打乱，只有用正确的密钥才能读取。

Security is a cross‑cutting responsibility. The OS authenticates users via passwords, biometrics or multi‑factor systems, then applies access rights to files and processes. Firewalls (often built into the OS) monitor network traffic, and user account control limits the ability of unauthorised programs to make system‑level changes. Keeping the OS and utilities updated with security patches is one of the most effective ways to defend against malware.

安全是一个贯穿各层面的责任。操作系统通过密码、生物识别或多因素系统验证用户身份，然后将访问权限应用于文件和进程。防火墙（常内建于操作系统）监控网络流量，用户账户控制则限制未授权程序进行系统级更改的能力。让操作系统和实用程序保持最新的安全补丁，是防御恶意软件最有效的方式之一。

9. Types of Operating Systems | 操作系统的类型

Different computing contexts demand different operating systems. WJEC expects you to recognise the main categories and their purposes.

不同的计算场景需要不同的操作系统。WJEC 要求你认识以下主要类别及其用途。

Desktop / laptop OS – Windows, macOS, Linux. Designed for single‑user multitasking with full GUI support and extensive hardware compatibility.
Mobile OS – Android, iOS. Optimised for touch input, power efficiency and app ecosystems; use sandboxing to isolate apps for security.
Server OS – Windows Server, Linux distributions. Prioritise stability, uptime, network services and the ability to handle many simultaneous connections.
Real‑time OS (RTOS) – Used in embedded systems like car engine controllers, medical devices and robotics. Guarantee a response within a strict time frame; safety‑critical systems cannot afford unpredictable delays.
Distributed OS – Manages a group of independent computers and makes them appear as a single system, often seen in cloud computing and large‑scale data processing.

桌面/笔记本操作系统 – Windows、macOS、Linux。面向单用户多任务，支持完整 GUI 并具备广泛的硬件兼容性。
移动操作系统 – 安卓、iOS。针对触控输入、功耗效率和应用生态进行优化；使用沙箱隔离应用以增强安全性。
服务器操作系统 – Windows Server、Linux 发行版。优先考虑稳定性、正常运行时间、网络服务以及处理大量并发连接的能力。
实时操作系统 (RTOS) – 用于汽车引擎控制器、医疗设备和机器人等嵌入式系统。保证在严格的时间范围内做出响应；安全关键系统不允许出现不可预测的延迟。
分布式操作系统 – 管理一组独立的计算机，使它们看起来像一个系统，常用于云计算和大规模数据处理。

10. The Boot Process and Interrupts | 启动过程与中断

When a computer is first powered on, the CPU loads a small fixed program from ROM called the BIOS (or UEFI firmware). The BIOS performs a Power‑On Self‑Test (POST) to check essential hardware like memory and keyboard. It then locates the boot loader on the designated boot device – usually the first sector of the hard drive – and hands over control. The boot loader pulls the operating system kernel from disk into RAM, and the OS takes over from there, loading drivers, services and, finally, the user interface.

电脑刚接通电源时，CPU 会从 ROM 加载一个叫做 BIOS（或 UEFI 固件）的小型固定程序。BIOS 执行开机自检（POST），检查内存和键盘等关键硬件。然后它在指定启动设备上（通常是硬盘的第一个扇区）找到引导加载程序，并将控制权交出。引导加载程序把操作系统内核从磁盘拉进内存，操作系统从此接管，依次加载驱动程序、服务，最后加载用户界面。

Interrupts are signals sent by hardware or software to gain the CPU’s attention. When an interrupt occurs, the OS temporarily suspends the current process, saves its state, and runs an Interrupt Service Routine (ISR) specific to that interrupt. This mechanism allows the CPU to react promptly to events like a mouse click, a timer tick (essential for pre‑emptive scheduling) or a network packet arrival, without wasting time continuously checking each device (polling).

中断是硬件或软件发送的信号，用于获取 CPU 的关注。中断发生时，操作系统暂时挂起当前进程，保存其状态，然后运行针对该中断的中断服务程序（ISR）。这种机制让 CPU 能立即响应诸如鼠标点击、定时器滴答（抢占式调度所必需）或网络数据包到达等事件，而无需浪费时间不断查询每个设备（轮询）。

Interrupts have priorities. A high‑priority interrupt (like a power failure warning) can pre‑empt a lower‑priority one. The OS stacks interrupts, ensuring that once the ISR finishes, the processor returns to the exact point where it was interrupted. This invisible dance is what makes a computer feel responsive.

中断具有优先级。高优先级中断（如电源故障警告）可以抢占低优先级中断。操作系统会将中断堆叠起来，确保中断服务程序结束后，处理器能回到被中断的精确位置。这一无形的舞蹈正是让电脑感觉反应灵敏的原因。

11. Key Terminology and Exam Tips | 关键术语与应试技巧

WJEC questions often mix multiple concepts into a single scenario. Below is a concise glossary of terms you must be able to define, compare and apply in context.

WJEC 的试题经常把多个概念融进一个情景里。下表是你必须能够在上下文中定义、比较和应用的关键术语简明词汇表。

Term	Definition	中文对照
Kernel	Core component of the OS that controls hardware at the lowest level	内核
Shell	The interface (CLI or GUI) through which a user communicates with the kernel	外壳
Paging	Dividing memory into fixed‑sized blocks to allow non‑contiguous allocation	分页
Swapping	Moving entire processes or pages between RAM and secondary storage	交换
Scheduler	OS component that decides which process runs next on the CPU	调度器
Driver	Software that translates OS commands into hardware‑specific instructions	驱动程序
ISR	Interrupt Service Routine; code that handles a specific interrupt	中断服务程序
Virtual memory	Using part of the hard disk as an extension of RAM	虚拟内存

When tackling an exam question, first identify which OS function is being tested – is it memory, processes, security or interfacing? Then structure your answer around key vocabulary and a clear sequence of cause and effect. Practice applying concepts to real‑world examples, such as explaining why a phone with limited RAM uses an RTOS‑like scheduler for touch responsiveness, or why a bank’s mainframe uses a server OS with high‑priority interrupt handling for transaction integrity.

做考试题目时，先识别题目测试的是哪一个操作系统功能——是内存、进程、安全还是接口？然后围绕关键术语和清晰的因果关系组织你的答案。练习将概念应用到现实世界的例子中，比如解释为什么内存有限的手机为了触摸响应而采用类似RTOS的调度器，或者为什么银行的大型机会使用具有高优先级中断处理的服务器操作系统来保障交易完整性。

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IGCSE WJEC Computer Science: Operating Systems | IGCSE WJEC计算机：操作系统