📚 Year 8 SQA Computing Science: Key Concepts Revision Guide | Year 8 SQA 计算机科学：核心知识点梳理
Welcome to your Year 8 SQA Computing Science revision guide. This article covers the essential topics you will meet in the Scottish broad general education curriculum: , including how computers represent data using binary, the internal hardware of a computer, memory, software, algorithms and programming basics in with Scratch and Python, testing and debugging, networks, and online safety. Each section pairs a short explanation with a worked example or table, so you can revise quickly and then test yourself against the checklist at the end.
欢迎阅读 Year 8 SQA 计算机科学复习指南。本文涵盖苏格兰基础教育阶段计算机科学课程的核心主题：计算机如何用二进制表示数据、计算机内部硬件、内存、软件、算法以及 Scratch 和 Python 编程基础、测试与调试、网络与网络安全。每一节都配有简短讲解和示例或表格，便于你快速复习，最后可用文末的复习清单进行自测。
1. Number Systems and Binary | 数字系统与二进制
Computers process data using the binary number system, which is base-2. Unlike the decimal system (base-10) that uses the digits 0-9, binary uses only two digits: 0 and 1. Each of these digits is called a 'bit', which is short for binary digit. Eight bits together make one byte, and four bits are sometimes called a nibble. Every piece of data inside a computer - a number, a letter, a photo, a sound - is stored as a pattern of bits.
计算机使用二进制（基数为 2）的数制处理数据。与使用 0-9 十个数字的十进制（基数为 10）不同，二进制只使用两个数字：0 和 1。每一位数字称为一个位（bit），即 binary digit 的缩写。八位组成一个字节（byte），四位有时称为半字节（nibble）。计算机内部的每一种数据——数字、字母、照片、声音——都以位模式存储。
The value of a binary digit depends on its position, just as in decimal. Moving one place to the left doubles the value of the column, so the place values are 128, 64, 32, 16, 8, 4, 2 and 1 for an 8-bit number.
与十进制一样，二进制位的值取决于它所处的位置。每向左移动一位，该列的权值就翻倍，因此 8 位数的位权依次是 128、64、32、16、8、4、2、1。
1×2³ + 0×2² + 1×2¹ + 1×2⁰ = 8 + 0 + 2 + 1 = 11
rs, then read them from bottom to top. For example, 45 ÷ 2 = 22 remainder 1, 22 ÷ 2 = 11 remainder 0, 11 ÷ 2 = 5 remainder 1, 5 ÷ 2 = 2 remainder 1, 2 ÷ 2 = 1 remainder 0, 1 ÷ 2 = 0 remainder 1 - reading upwards gives 101101₂.
因此，二进制数 1011₂ 等于十进制数 11。若要从十进制转换为二进制，可反复除以 2 并记录余数，再从下往上读取。例如：45 ÷ 2 = 22 余 1，22 ÷ 2 = 11 余 0，11 ÷ 2 = 5 余 1，5 ÷ 2 = 2 余 1，2 ÷ 2 = 1 余 0，1 ÷ 2 = 0 余 1，自下而上读取得到 101101₂。
| Bit Position | 2⁷ | 2⁶ | 2⁵ | 2⁴ | 2³ | 2² | 2¹ | 2⁰ |
| Place value | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
| 1011₂ | 0 | 0 | 0 | 0 | 1 | 0 | 1 | 1 |
ert fluently at Year 8, but you should recognise the idea that different number bases are simply different ways of writing the same value.
十六进制（基数为 16）有时被用作简写，因为每一位十六进制数恰好对应四位二进制：1011 1101₂ = BD₁₆。Year 8 阶段不要求熟练换算，但应理解不同进制只是同一个数值的不同写法。
2. Data Representation: Text, Images, Sound and Video | 数据表示：文本、图像、声音与视频
All data must be converted into binary before a computer can store or process it. Text is represented using a character set. ASCII uses 7 or 8 bits per character, which is enough for English letters, digits and punctuation. Unicode uses more bits and can represent characters from every writing system, including Chinese characters and emoji.
计算机在存储或处理任何数据之前，都必须先把它转换为二进制。文本使用字符集表示：ASCII 每个字符用 7 位或 8 位，足以表示英文字母、数字和标点；Unicode 使用更多位，可以表示世界上各种书写系统的字符，包括汉字和表情符号。
A bitmap image is stored as a grid of pixels. Each pixel has a binary code for its colour. The number of pixels across and down is the resolution, and the number of bits used per pixel is the colour depth. A higher resolution and a larger colour depth give a sharper image but produce a much bigger file.
位图图像以像素网格存储，每个像素的颜色用一个二进制编码表示。横向和纵向的像素数量称为分辨率，每个像素使用的位数称为色彩深度。分辨率越高、色彩深度越大，图像越清晰，但文件也大得多。
Image file size (bits) = width × height × colour depth
Sound is an analogue wave, so it must be sampled to become digital. The sample rate is how many times per second the wave is measured, and the bit depth is how precisely each measurement is recorded. A higher sample rate and bit depth give better quality but a larger file. Video is simply a sequence of still images called frames played fast enough to look continuous.
声音是模拟波形，必须经过采样才能数字化。采样率是每秒测量波形的次数，位深是每次测量的精度。采样率和位深越高，音质越好，文件也越大。视频则是一系列静止画面（帧）以足够快的速度播放，从而看起来是连续的。
| Unit | Size | Typical example |
| 1 bit | a single 0 or 1 | one switch on or off |
| 1 byte | 8 bits | one ASCII character |
| 1 kilobyte (KB) | 1024 bytes | a short text file |
| 1 megabyte (MB) | 1024 KB | a high-quality photo |
| 1 gigabyte (GB) | 1024 MB | a short video clip |
3. Computer Hardware: Input, Output, Processing and Storage | 计算机硬件：输入、输出、处理与存储
Hardware means the physical parts of a computer system that you can touch. It is usually grouped into four categories: input devices, output devices, processing devices and storage devices. A keyboard, mouse, microphone, webcam, touchscreen and scanner are input devices - they send data into the system. A monitor, printer, speaker, projector and headphones are output devices - they present the results of processing.
硬件是指计算机系统中可以触摸到的物理部件，通常分为四类：输入设备、输出设备、处理设备和存储设备。键盘、鼠标、麦克风、摄像头、触摸屏、扫描仪属于输入设备，把数据送入系统；显示器、打印机、音箱、投影仪、耳机属于输出设备，用来呈现处理结果。
The processor, or CPU (central processing unit), is the 'brain' of the computer. It contains the control unit, which fetches and decodes instructions and controls the flow of data, and the arithmetic logic unit (ALU), which carries out calculations and comparisons. The CPU repeats the fetch-decode-execute cycle many millions of times per second. Its speed is measured in hertz, usually gigahertz (GHz), and the number of cores tells you how many instructions it can work on at once.
处理器即 CPU（中央处理器），是计算机的"大脑"。它包含控制单元（负责取指令、译码并控制数据流动）和算术逻辑单元 ALU（执行运算和比较）。CPU 每秒重复"取指—译码—执行"周期数百万次。其速度以赫兹为单位，通常用吉赫兹（GHz）表示；核心数量表示它可以同时处理多少条指令。
Storage keeps data permanently, even when the power is switched off. Magnetic storage such as a hard disk drive (HDD) is cheap and holds a lot of data but has moving parts. Solid state storage (SSD, USB flash drive, SD card) is faster and more robust but usually costs more per gigabyte. Optical storage such as CD, DVD and Blu-ray uses a laser to read the disc.
存储设备即使在断电后也能永久保存数据。磁存储如硬盘（HDD）价格便宜、容量大，但有机械活动部件；固态存储（SSD、U 盘、SD 卡）速度更快、更耐用，但每 GB 价格通常更高；光盘存储如 CD、DVD、蓝光则使用激光读取数据。
4. Memory: RAM, ROM and Cache | 内存：RAM、ROM 与缓存
Memory is where programs and data are held while the computer is working. RAM (random access memory) is volatile, which means its contents are lost when the power goes off. It stores the operating system, the programs currently running and the data being used. Having more RAM allows more programs to run at once without slowing down.
内存是计算机工作时存放程序和数据的地方。RAM（随机存取存储器）是易失性的，断电后内容会丢失。它存放操作系统、当前运行的程序以及正在使用的数据。RAM 越大，可以同时运行的程序就越多而不至于变慢。
ROM (read-only memory) is non-volatile and normally read-only, so its contents stay even without power. It holds the bootstrap loader and the start-up instructions (the BIOS or UEFI firmware) that tell the computer how to begin loading the operating system. Cache is a small amount of very fast memory inside or close to the CPU that stores frequently used instructions to speed up processing.
ROM（只读存储器）是非易失性的，通常只能读取，断电后内容仍保留。它存放引导加载程序和启动指令（BIOS 或 UEFI 固件），告诉计算机如何开始加载操作系统。缓存（cache）是位于 CPU 内部或附近的一小块高速存储器，用于存放常用指令，从而加快处理速度。
If RAM becomes full, the operating system can move data to a section of the hard drive called virtual memory. This prevents programs from crashing, but it is much slower than RAM because data must be read from the disk.
如果 RAM 被占满，操作系统可以把数据转移到硬盘上称为虚拟内存的区域。这可以避免程序崩溃，但由于要从磁盘读取数据，速度比 RAM 慢得多。
5. Software: System and Application Software | 软件：系统软件与应用软件
Software is the set of programs and instructions that tell the hardware what to do. It is divided into two main types. System software runs the computer itself and includes the operating system and utility programs. Application software helps the user carry out a specific task, such as writing a document, editing a photo, browsing the web or playing a game.
软件是告诉硬件该做什么的程序和指令集合，主要分为两类。系统软件负责运行计算机本身，包括操作系统和实用工具程序；应用软件帮助用户完成特定任务，例如写文档、修图、上网或玩游戏。
The operating system performs several essential jobs: managing memory and storage, scheduling the processor, controlling input and output devices, providing a user interface, managing user accounts and permissions, and handling files. Examples you may have used include Windows, macOS, Linux, iOS and Android.
操作系统承担多项关键任务：管理内存和存储、调度处理器、控制输入输出设备、提供用户界面、管理用户账户与权限以及处理文件。你可能用过的例子包括 Windows、macOS、Linux、iOS 和 Android。
Software can also be described by its licence. Proprietary software is owned by a company and you usually pay for it and cannot see or change the source code. Open source software makes the source code available so anyone can study, modify and improve it. Freeware is free to use but the source code stays closed, while utility software such as antivirus tools, disk defragmenters and backup tools helps keep the system healthy.
软件还可以按授权方式分类。专有软件的源码归公司所有，通常需要付费，且不能查看或修改源代码；开源软件公开源代码，任何人都可以研究、修改和改进；免费软件可以免费使用，但源代码不公开；杀毒工具、磁盘碎片整理和备份工具等实用程序则用于维护系统健康。
6. Algorithms and Computational Thinking | 算法与计算思维
An algorithm is a step-by-step set of instructions for solving a problem or completing a task. Computational thinking is the set of skills used to design algorithms, and it has four main parts: decomposition (breaking a big problem into smaller ones), pattern recognition (spotting similarities between problems), abstraction (removing unnecessary detail) and algorithm design (writing the steps in order).
算法是解决问题或完成任务的一步步指令。计算思维是设计算法时使用的技能，包含四个主要方面：分解（把大问题拆成小问题）、模式识别（发现问题之间的相似之处）、抽象（去掉不必要的细节）以及算法设计（按顺序写出步骤）。
Algorithms can be written as pseudocode, which looks like a simplified programming language but has no strict rules, or as a flowchart using standard symbols. A terminator (oval) starts and ends the program, a process (rectangle) carries out an action, an input/output (parallelogram) reads or displays data, and a decision (diamond) asks a question with yes/no answers.
算法可以用伪代码书写，它像简化版的编程语言但规则不严格；也可以用流程图表示，使用标准图形：起止框（椭圆）表示开始和结束，处理框（矩形）表示执行动作，输入输出框（平行四边形）表示读取或显示数据，判断框（菱形）表示带"是/否"答案的问题。
Every program is built from three control structures. Sequence means instructions run one after another. Selection means the program chooses between different paths using if, then and else. Iteration means instructions repeat, either a fixed number of times or while a condition is true.
任何程序都由三种控制结构组成：顺序结构表示指令依次执行；选择结构表示程序用 if、then、else 在不同路径间做出选择；循环结构表示指令重复执行，可以固定次数重复，也可以在条件为真时重复。
7. Programming with Scratch | 使用 Scratch 编程
Scratch is a block-based programming language, which means you drag and snap coloured blocks together instead of typing code. This makes it ideal for learning the logic of programming without worrying about spelling mistakes. The main parts of the screen are the stage, where the program runs, the sprite list of characters and objects, and the block palette organised into categories.
Scratch 是一种积木式编程语言，你只需拖拽并拼合彩色积木，而无需输入代码。这使它非常适合在不受拼写错误干扰的情况下学习编程逻辑。界面主要由舞台（程序运行的地方）、角色列表（人物和对象）以及按类别排列的积木区组成。
The block categories you must know are Motion, Looks, Sound, Events, Control, Sensing, Operators, Variables and My Blocks. Events blocks such as 'when green flag clicked' start a script, Control blocks such as 'repeat', 'forever' and 'if...then...else' handle iteration and selection, and Operators blocks handle arithmetic and comparison.
必须掌握的积木类别有：运动、外观、声音、事件、控制、侦测、运算、变量和自制积木。事件类积木如"当绿旗被点击"用于启动脚本；控制类积木如"重复执行""一直重复""如果……那么……否则"处理循环与选择；运算类积木处理算术和比较。
A simple useful script is a seconds converter. Ask the user for a number of seconds, then use the operators to divide by 60 to find minutes and use 'mod' or subtraction to find the remaining seconds, and say the result. Variables store values that can change, such as score or lives, while lists store many values in order. The 'broadcast' block sends a message that starts scripts in other sprites, which is how you make parts of a game work together.
一个简单实用的脚本是"秒数换算器"：询问用户秒数，用运算积木除以 60 求出分钟，再用取余或减法求出剩余秒数，最后说出结果。变量存放可以改变的值，如分数或生命值；列表按顺序存放多个值。"广播"积木可以发送消息并启动其他角色的脚本，这正是让游戏的各个部分协同工作的方式。
8. Programming with Python | 使用 Python 编程
Python is a text-based programming language. Unlike Scratch, you type the code, so correct spelling, punctuation and indentation matter. A first program uses print() to display output and input() to read data from the user. Remember that input() always returns a string, so you must convert it with int() or float() before doing arithmetic.
Python 是一种文本式编程语言。与 Scratch 不同，你需要自己输入代码，因此拼写、标点和缩进都非常重要。第一个程序通常使用 print() 输出内容，用 input() 读取用户输入。要记住 input() 返回的总是字符串，因此做算术运算前必须用 int() 或 float() 进行转换。
age = int(input("Enter your age: ")) → print("Next year you will be", age + 1)
Selection in Python uses if, elif and else, and the condition line always ends with a colon. Iteration uses for loops when you know how many times to repeat, and while loops when you repeat until a condition changes. Indentation of four spaces shows which lines belong inside the loop or the if block.
Python 中的选择结构使用 if、elif 和 else，条件行末尾必须加冒号。循环结构中，for 循环用于已知重复次数的情况，while 循环用于重复直到条件改变的情况。四个空格的缩进表示哪些语句属于循环体或 if 语句块。
| Concept | Python example | Purpose |
| Output | print("Hello") | displays text on screen |
| Variable | score = 0 | stores a value with a name |
| Selection | if score > 10: | chooses between paths |
| Iteration | for i in range(5): | repeats code five times |
| List | names = ["Ava", "Ben"] | stores several items in order |
| Function | def area(w, h): | reusable block of code |
Python is also excellent for working with strings and lists. You can find the length of a string with len(), join strings with
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