| Candidates should be able to: | Notes and guidance |
|---|---|
| 1 (a) Understand the role of the central processing unit (CPU) in a computer | • The CPU processes instructions and data that are input into the computer so that the result can be output |
| (b) Understand what is meant by a microprocessor | • A microprocessor is a type of integrated circuit on a single chip |
| 2 (a) Understand the purpose of the components in a CPU, in a computer that has a Von Neumann architecture | • Including: – units: arithmetic logic unit (ALU) and control unit (CU) – registers: program counter (PC), memory address register (MAR), memory data register (MDR), current instruction register (CIR) and accumulator (ACC) – buses: address bus, data bus and control bus |
| (b) Describe the process of the fetch–decode–execute (FDE) cycle, including the role of each component in the process | • How instructions and data are fetched from random access memory (RAM) into the CPU, how they are processed using each component and how they are then executed • Storing data and addresses into specific registers • Using buses to transmit data, addresses and signals • Using units to fetch, decode and execute data and instructions |
| 3 Understand what is meant by a core, cache and clock in a CPU and explain how they can affect the performance of a CPU | • The number of cores, size of the cache and speed of the clock can affect the performance of a CPU |
| 4 Understand the purpose and use of an instruction set for a CPU | • An instruction set is a list of all the commands that can be processed by a CPU, and the commands are machine code |
| 5 Describe the purpose and characteristics of an embedded system and identify devices in which they are commonly used | • An embedded system is used to perform a dedicated functions. For example in, domestic appliances, cars, security systems, lighting systems or vending machines. This is different to a general purpose computer that is used to perform many different functions. For example in, a personal computer (PC) or a laptop |
硬件
IGCSE 计算机科学 · 第 3 主题
3.1
计算机体系结构
大纲
来源:剑桥国际大纲
中央处理器(central processing unit,CPU)是计算机处理数据并执行指令(instructions)的部分。它通过重复一个周期、每秒数百万次来运行程序。
Parts of the CPU
| 部分 | 它做什么 |
|---|---|
| 算术逻辑单元(arithmetic logic unit,ALU) | 做计算(加、减)和逻辑操作(比较) |
| 控制单元(control unit,CU) | 发送控制信号以管理所有部分并告诉它们做什么 |
| 寄存器(registers) | 非常小、非常快的存储,一次容纳一份数据 |
各部分由总线(buses,携带信息的成组导线)连接:
- 地址总线(address bus)携带内存地址(一个方向);
- 数据总线(data bus)携带数据和指令(两个方向);
- 控制总线(control bus)携带控制信号。
Special registers
这些寄存器在取指-执行周期期间被使用。
| 寄存器 | 目的 |
|---|---|
| 程序计数器(program counter,PC) | 容纳下一条指令的地址 |
| 内存地址寄存器(memory address register,MAR) | 容纳要读取或写入的地址 |
| 内存数据寄存器(memory data register,MDR) | 容纳刚取的数据或指令 |
| 当前指令寄存器(current instruction register,CIR) | 容纳现在正被执行的指令 |
| 累加器(accumulator,ACC) | 容纳 ALU 计算的结果 |
The fetch–execute cycle
取指执行周期(fetch–execute cycle)有三个阶段,一遍又一遍地重复:
- 取指——指令从内存(memory)被复制进 CPU(用 PC、MAR 和 MDR)。PC 随即增加 1。
- 译码——控制单元算出指令的意思。
- 执行——指令被执行(ALU 可能做一个计算,结果去累加器)。
Cache memory
高速缓存(cache)是 CPU 内部或靠近它的少量非常快的内存。它存储 CPU 常用的数据和指令。CPU 从高速缓存读取比从主存快得多,所以计算机运行得更快。
What affects CPU performance
| 特性 | 效果 |
|---|---|
| 核心(cores)的数目 | 每个核心能自己运行指令,所以更多的核心能同时做更多的工作 |
| 高速缓存大小 | 一个更大的高速缓存为 CPU 容纳更多准备好的数据,所以它等得更少 |
| 时钟速度(clock speed) | 每秒的周期数;一个更高的时钟速度每秒运行更多的指令 |
例题。 两台电脑除以下不同外完全相同:A 是 3.0 GHz 单核 CPU,带 2 MB 缓存;B 是 2.4 GHz 四核 CPU,带 8 MB 缓存。哪一台更适合视频剪辑?为什么?视频剪辑可以拆成许多能同时进行的任务,所以 B 的四个核心可以并行处理多路数据,而 A 一次只能处理一路。B 更大的缓存也把更多常用数据留在离 CPU 很近的地方,所以它需要从 RAM 取数的次数更少。尽管 A 的主频更高,B 仍是更好的选择。不要只凭主频作答:要把核心数、缓存和主频放在一起权衡,并把每一项都联系到具体要做的工作。
Embedded systems
一个嵌入式系统(embedded system)是建在一个更大的设备内部做一件固定工作的一台小计算机。它专门用于那个任务,通常小而低成本,而且没有通用操作系统。例子:一台洗衣机、一个微波炉、一个机顶盒。
探索
The fetch-execute cycle
Tap round the loop the CPU repeats billions of times a second — fetch the instruction, decode what it means, execute it, then do it all again.
词汇表
训练
| 英文 | 中文 | 拼音 |
|---|---|---|
| central processing unit | 中央处理器 | zhōng yāng chǔ lǐ qì |
| instructions | 指令 | zhǐ lìng |
| arithmetic logic unit | 算术逻辑单元 | suàn shù luó jí dān yuán |
| control unit | 控制单元 | kòng zhì dān yuán |
| registers | 寄存器 | jì cún qì |
| buses | 总线 | zǒng xiàn |
| address bus | 地址总线 | dì zhǐ zǒng xiàn |
| data bus | 数据总线 | shù jù zǒng xiàn |
| control bus | 控制总线 | kòng zhì zǒng xiàn |
| program counter | 程序计数器 | chéng xù jì shù qì |
| memory address register | 内存地址寄存器 | nèi cún dì zhǐ jì cún qì |
| memory data register | 内存数据寄存器 | nèi cún shù jù jì cún qì |
| current instruction register | 当前指令寄存器 | dāng qián zhǐ lìng jì cún qì |
| accumulator | 累加器 | lěi jiā qì |
| fetch–execute cycle | 取指执行周期 | qǔ zhǐ zhí xíng zhōu qī |
| Cache | 高速缓存 | gāo sù huǎn cún |
| cores | 核心 | hé xīn |
| clock speed | 时钟速度 | shí zhōng sù dù |
| embedded system | 嵌入式系统 | qiàn rù shì xì tǒng |
| memory | 内存 | nèi cún |
3.2
输入与输出设备
大纲
| Candidates should be able to: | Notes and guidance |
|---|---|
| 1 Understand what is meant by an input device and why it is required | • Including: – barcode scanner – digital camera – keyboard – microphone – optical mouse – QR code scanner – touch screen (resistive, capacitive and infra-red) – two-dimensional (2D) and three-dimensional (3D) scanners |
| 2 Understand what is meant by an output device and why it is required | • Including: – actuator – digital light processing (DLP) projector – inkjet printer – laser printer – light emitting diode (LED) screen – liquid crystal display (LCD) projector – liquid crystal display (LCD) screen – speaker – 3D printer |
| 3 (a) Understand what is meant by a sensor and the purposes of sensors | • Limited to: – acoustic – accelerometer – flow – gas – humidity – infra-red – level – light – magnetic field – moisture – pH – pressure – proximity – temperature |
| (b) Identify the type of data captured by each sensor and understand when each sensor would be used, including selecting the most suitable sensor for a given context |
来源:剑桥国际大纲
一个输入设备把数据发送进计算机。
| 设备 | 它如何工作 |
|---|---|
| 条形码扫描器(barcode scanner) | 向条照光并读取反射回来的图案 |
| 二维码扫描器(QR code scanner) | 一个摄像头读取黑白块的一个方形图案 |
| 键盘 | 按一个键发送那个字符的一个代码 |
| 光电鼠标(optical mouse) | 一个光和一个传感器跟踪跨一个表面的移动 |
| 麦克风 | 把声波变成一个电信号 |
| 数码相机 | 一个镜头把光聚焦到一个记录像素的传感器上 |
| 传感器(sensors) | 测量一个物理量(如温度或光)并把它作为数据发送 |
| 触摸屏(touch screen) | 检测你的手指触碰屏幕的地方 |
一个触摸屏能以三种方式工作:
- 电阻式(resistive)——两层在你触碰的地方被压在一起;
- 电容式(capacitive)——它感知你手指的微小电荷;
- 红外线(infrared)——你的手指打破一个光束的网格。
探索
Device and storage lab
Classify computing examples by what job they do in a system.
词汇表
训练
| 英文 | 中文 | 拼音 |
|---|---|---|
| barcode scanner | 条形码扫描器 | tiáo xíng mǎ sǎo miáo qì |
| QR code scanner | 二维码扫描器 | èr wéi mǎ sǎo miáo qì |
| sensors | 传感器 | chuán gǎn qì |
| touch screen | 触摸屏 | chù mō píng |
| resistive | 电阻式 | diàn zǔ shì |
| capacitive | 电容式 | diàn róng shì |
| infrared | 红外线 | hóng wài xiàn |
| optical mouse | 光电鼠标 | guāng diàn shǔ biāo |
3.2
输出设备
一个输出设备把数据从计算机发送出到用户。
| 设备 | 它如何工作 |
|---|---|
| 执行器(actuator) | 把一个电信号变成运动(例如一个马达或阀门) |
| LCD/LED 屏幕 | 用一个微小彩色点的网格显示图像 |
| 投影仪(projector) | 把一个放大的图像照到一面墙或屏幕上 |
| 喷墨打印机(inkjet printer) | 向纸喷微小的墨滴 |
| 激光打印机(laser printer) | 用一个激光和被热固定到纸上的粉末(碳粉) |
| 3D 打印机 | 一层一层地构建一个固体物体 |
| 扬声器(speaker) | 把一个电信号变成声音 |
词汇表
训练
| 英文 | 中文 | 拼音 |
|---|---|---|
| actuator | 执行器 | zhí xíng qì |
| projector | 投影仪 | tóu yǐng yí |
| inkjet printer | 喷墨打印机 | pēn mò dǎ yìn jī |
| laser printer | 激光打印机 | jī guāng dǎ yìn jī |
| speaker | 扬声器 | yáng shēng qì |
3.3
数据存储
大纲
| Candidates should be able to: | Notes and guidance |
|---|---|
| 1 Understand what is meant by primary storage | • Primary storage is directly accessed by the CPU • Including the role of: – random access memory (RAM) – read only memory (ROM) • Including why a computer needs both RAM and ROM, and the difference between them |
| 2 Understand what is meant by secondary storage | • Secondary storage is not directly accessed by the CPU and is necessary for more permanent storage of data |
| 3 Describe the operation of magnetic, optical and solid-state (flash memory) storage and give examples of each | • Magnetic storage uses platters which are divided into tracks and sectors. Data is read and written using electromagnets. Including hard disk drive (HDD) • Optical storage uses lasers to create and read pits and lands. Including: CD, DVD and Blu-ray • Solid-state (flash memory) uses NAND or NOR technology. Transistors are used as control gates and floating gates. Including: solid-state drive (SSD), SD card and USB drive |
| 4 Describe what is meant by virtual memory, how it is created and used and why it is necessary | • Pages of data are transferred between RAM and virtual memory when needed |
| 5 Understand what is meant by cloud storage | • Cloud storage can be accessed remotely in comparison to storing data locally |
| 6 Explain the advantages and disadvantages of storing data on the cloud in comparison to storing it locally | • Physical servers and storage are needed to store data in cloud storage |
来源:剑桥国际大纲
主存储器(primary storage)是 CPU 能直接使用的内存。有两种。
| RAM | ROM | |
|---|---|---|
| 全名 | 随机存取存储器(random access memory) | 只读存储器(read only memory) |
| 读/写 | 读和写 | 只读 |
| 没有电时保留数据? | 否——它是易失性(volatile)的 | 是——它是非易失性(non-volatile)的 |
| 容纳 | 现在使用中的程序和数据 | 启动指令(如何引导计算机) |
两者都需要:ROM 告诉计算机如何启动,然后 RAM 容纳你运行的程序。
词汇表
训练
| 英文 | 中文 | 拼音 |
|---|---|---|
| Primary storage | 主存储器 | zhǔ cún chǔ qì |
| random access memory | 随机存取存储器 | suí jī cún qǔ cún chǔ qì |
| read only memory | 只读存储器 | zhī dú cún chǔ qì |
| volatile | 易失性 | yì shī xìng |
| non-volatile | 非易失性 | fēi yì shī xìng |
3.3
辅助存储
辅助存储器(secondary storage)永久地保留数据,即使电关了。它是非易失性的,被用于长期存储。有三种类型。
| 类型 | 它如何存储数据 | 例子 |
|---|---|---|
| 磁存储(magnetic storage) | 数据作为旋转磁盘上被磁化的斑点存储 | 硬盘驱动器(HDD)、磁带 |
| 光存储(optical storage) | 数据作为被一个激光读取的标记存储 | CD、DVD、蓝光 |
| 固态存储(solid state storage) | 数据存储在闪存(flash memory)中,没有移动部件 | SSD、USB 闪存盘、存储卡 |
探索
Device and storage lab
Classify computing examples by what job they do in a system.
词汇表
训练
| 英文 | 中文 | 拼音 |
|---|---|---|
| Secondary storage | 辅助存储器 | fǔ zhù cún chǔ qì |
| magnetic storage | 磁存储 | cí cún chǔ |
| optical storage | 光存储 | guāng cún chǔ |
| solid state storage | 固态存储 | gù tài cún chǔ |
| flash memory | 闪存 | shǎn cún |
3.3
虚拟内存
当 RAM 变满时,计算机能把辅助存储的一部分用作额外的、假装的 RAM。这叫虚拟内存(virtual memory)。
现在不需要的数据被从 RAM 移出到磁盘上,这为其他程序在 RAM 中腾出空间。这让你运行比单独的 RAM 能容纳的更多的程序。它更慢,因为辅助存储比 RAM 慢得多。
词汇表
训练
| 英文 | 中文 | 拼音 |
|---|---|---|
| virtual memory | 虚拟内存 | xū nǐ nèi cún |
3.3
数据存储
大纲
| Candidates should be able to: | Notes and guidance |
|---|---|
| 1 Understand what is meant by primary storage | • Primary storage is directly accessed by the CPU • Including the role of: – random access memory (RAM) – read only memory (ROM) • Including why a computer needs both RAM and ROM, and the difference between them |
| 2 Understand what is meant by secondary storage | • Secondary storage is not directly accessed by the CPU and is necessary for more permanent storage of data |
| 3 Describe the operation of magnetic, optical and solid-state (flash memory) storage and give examples of each | • Magnetic storage uses platters which are divided into tracks and sectors. Data is read and written using electromagnets. Including hard disk drive (HDD) • Optical storage uses lasers to create and read pits and lands. Including: CD, DVD and Blu-ray • Solid-state (flash memory) uses NAND or NOR technology. Transistors are used as control gates and floating gates. Including: solid-state drive (SSD), SD card and USB drive |
| 4 Describe what is meant by virtual memory, how it is created and used and why it is necessary | • Pages of data are transferred between RAM and virtual memory when needed |
| 5 Understand what is meant by cloud storage | • Cloud storage can be accessed remotely in comparison to storing data locally |
| 6 Explain the advantages and disadvantages of storing data on the cloud in comparison to storing it locally | • Physical servers and storage are needed to store data in cloud storage |
来源:剑桥国际大纲
云存储(cloud storage)把你的数据保存在通过互联网访问的远程物理服务器上,而不是在你自己的设备上。
- 优点:从任何地方任何设备访问它;没有本地存储硬件要购买或维护;容易分享文件和自动备份。
- 缺点:需要一个可用的互联网连接;持续的订阅成本;安全和隐私取决于提供商;你依赖那个提供商保持可用和在营。
词汇表
训练
| 英文 | 中文 | 拼音 |
|---|---|---|
| Cloud storage | 云存储 | yún cún chǔ |
3.4
网络硬件
大纲
| Candidates should be able to: | Notes and guidance |
|---|---|
| 1 Understand that a computer needs a network interface card (NIC) to access a network | |
| 2 Understand what is meant by, and the purpose of, a media access control (MAC) address, including its structure | • A network interface card is given a MAC address at the point of manufacture • MAC addresses are usually written as hexadecimal • MAC addresses are created using the manufacturer code and the serial code |
| 3 (a) Understand what is meant by, and the purpose of, an internet protocol (IP) address (b) Understand that there are different types of IP address | • An IP address is allocated by the network and it can be static or dynamic • Including the characteristics of, and differences between, IPv4 and IPv6 |
| 4 Describe the role of a router in a network | • A router sends data to a specific destination on a network • A router can assign IP addresses • A router can connect a local network to the internet |
来源:剑桥国际大纲
Network interface card (NIC)
一个网络接口卡(network interface card,NIC)是让一个设备加入一个网络并发送和接收数据的硬件。每个 NIC 有一个内建的 MAC 地址。
MAC address and IP address
- 一个 MAC 地址(media access control 介质访问控制 地址)是一个识别一个物理设备的数。制造商设定它,而它通常不改变。它用十六进制书写。
- 一个 IP 地址(internet protocol 网际协议 地址)是一个识别一个网络上的一个设备的数。它由网络给出并能改变。
所以一个 MAC 地址随设备,而一个 IP 地址取决于设备正在使用的网络。
IP 地址有两个版本。IPv4 是 32 位的,写成四个 0–255 的十进制数(例如 192.168.0.1);较新的 IPv6 是 128 位的,写成用冒号分隔的八组十六进制数,提供多得多的地址。一个地址还要么是静态(static)的(固定、手动设置、从不改变),要么是动态(dynamic)的(每次设备连接时由路由器/网络分发,所以能改变)。
Router
一个路由器(router)把不同的网络连接在一起——例如,你的家庭网络连到互联网。它读每个数据包中的 IP 地址并把它转发向正确的网络。
探索
Network route lab
Follow data from a device through network hardware and protocols.
词汇表
训练
| 英文 | 中文 | 拼音 |
|---|---|---|
| network interface card | 网络接口卡 | wǎng luò jiē kǒu kǎ |
| static | 静态 | jìng tài |
| dynamic | 动态 | dòng tài |
| router | 路由器 | lù yóu qì |
| fetch-execute cycle | 取指执行周期 | qǔ zhǐ zhí xíng zhōu qī |
| media access control | 介质访问控制 | jiè zhì fǎng wèn kòng zhì |
| internet protocol | 网际协议 | wǎng jì xié yì |
3.4
考试技巧
- 学习取指-译码-执行周期和特殊寄存器:程序计数器容纳下一条指令的地址,MAR/MDR 携带地址/数据,而累加器容纳 ALU 的结果。
- CPU 性能随更多的核心、一个更大的高速缓存和一个更高的时钟速度改善。
- RAM 是易失性的(它在没有电时失去它的数据)并容纳使用中的程序;ROM 是非易失性的且只读(启动指令)。
- 匹配辅助存储类型:磁(HDD、磁带)、光(CD/DVD,被一个激光读取)、固态(SSD、USB、闪存——没有移动部件)。
- 一个 MAC 地址识别物理设备且通常不改变;一个 IP 地址由网络给出并能改变。
本主题的互动课程
逐步学习,并即时检测练习。