📚 Year 9 SQA Computing: Key Concepts Overview | Year 9 SQA 计算机：核心知识点梳理
This revision guide summarises all the core topics you need to master for Year 9 SQA Computing. We cover computer hardware, data representation, logic, networks, security, and programming fundamentals in clear bilingual explanations.
本复习指南汇总了 Year 9 SQA 计算机学科需要掌握的所有核心主题。我们以清晰的中英双语解释涵盖计算机硬件、数据表示、逻辑、网络、安全和编程基础。
1. Computer System Fundamentals | 计算机系统基础
A computer system is made up of hardware and software working together. Hardware includes physical parts such as the CPU, RAM, hard drive, and input/output devices. Software consists of the programs and applications that tell the hardware what to do.
计算机系统由硬件和软件协同工作组成。硬件包括 CPU、内存、硬盘以及输入/输出设备等物理部件。软件则是由程序和应用程序组成，它们指示硬件执行相应的操作。
The central processing unit (CPU) executes instructions using a fetch–decode–execute cycle. It contains the control unit (CU) to manage data flow and the arithmetic logic unit (ALU) to perform calculations.
中央处理器 (CPU) 通过“取指–译码–执行”周期来执行指令。它包含控制单元 (CU) 以管理数据流，以及算术逻辑单元 (ALU) 来执行计算。
The motherboard connects all components and allows communication between them. Power supply, cooling fans, and expansion slots are also essential parts of a computer's hardware.
主板连接所有组件并允许它们之间进行通信。电源、散热风扇和扩展插槽也是计算机硬件的重要部分。
2. Data Representation: Binary Numbers | 数据表示：二进制数
Computers use binary (base-2) because they rely on two states: on (1) and off (0). Every number, character, image, or sound is ultimately stored as sequences of 0s and 1s.
计算机使用二进制（基数为 2），因为它们只依赖于两种状态：开（1）和关（0）。每个数字、字符、图像或声音最终都以 0 和 1 的序列存储。
To convert a binary number to decimal, multiply each bit by its place value (powers of 2) and sum the results. For example, the binary number 1011₂ equals:
要将二进制数转换为十进制，将每位乘以其位值（2 的幂）并求和。例如，二进制数 1011₂ 等于：
1011₂ = (1×2³) + (0×2²) + (1×2¹) + (1×2⁰) = 8 + 0 + 2 + 1 = 11₁₀
The leftmost bit in a binary number is the most significant bit (MSB), and the rightmost is the least significant bit (LSB). Adding leading zeros does not change the value.
二进制数中最左边的位是最高有效位 (MSB)，最右边的位是最低有效位 (LSB)。添加前导零不会改变数值。
s a shorthand for binary. One hex digit represents four binary digits (a nibble). Digits 0–9 and letters A–F are used, where A=10, B=11, ..., F=15.
十六进制（基数为 16）常被用作二进制的简写。一个十六进制数字表示四个二进制位（半个字节）。使用数字 0–9 和字母 A–F，其中 A=10、B=11……F=15。
3. Data Representation: Text, Images & Sound | 数据表示：文本、图像与声音
Text is stored using character sets such as ASCII and Unicode. ASCII uses 7 or 8 bits to represent 128 or 256 characters. Unicode extends this to represent thousands of characters from different languages, using up to 32 bits per character.
文本使用字符集（如 ASCII 和 Unicode）存储。ASCII 使用 7 或 8 位来表示 128 或 256 个字符。Unicode 将其扩展，可表示来自不同语言的数千个字符，每个字符最多使用 32 位。
Images are represented as a grid of pixels, with each pixel assigned a binary colour value. In a black-and-white image, one bit per pixel (0 for black, 1 for white) may be sufficient. Colour images use more bits per pixel to encode RGB values. Resolution and colour depth determine the file size.
图像表示为像素网格，每个像素被赋予一个二进制颜色值。在黑白图像中，每个像素 1 位（0 表示黑色，1 表示白色）可能就足够了。彩色图像使用更多位来编码 RGB 值。分辨率和颜色深度决定了文件大小。
Sound is captured by sampling the amplitude of a wave at regular intervals. The sample rate (measured in Hz) and bit depth affect the quality and size of the digital audio file. Higher sample rate and bit depth give better quality but larger files.
声音通过定期对波形振幅进行采样来捕获。采样率（以 Hz 为单位）和位深影响数字音频文件的质量和大小。采样率和位深越高，质量越好，但文件也越大。
4. Logic Gates and Truth Tables | 逻辑门与真值表
Logic gates are the building blocks of digital circuits. The three basic gates are AND, OR, and NOT. Each gate takes one or more binary inputs and produces a single binary output.
逻辑门是数字电路的基本构建块。三种基本门是 AND、OR 和 NOT。每个门接收一个或多个二进制输入并产生单个二进制输出。
An AND gate outputs 1 only if all inputs are 1. An OR gate outputs 1 if at least one input is 1. A NOT gate (inverter) flips the input: 1 becomes 0, 0 becomes 1.
AND 门仅在所有输入均为 1 时才输出 1。OR 门只要至少有一个输入为 1 就输出 1。NOT 门（反相器）翻转输入：1 变为 0，0 变为 1。
Truth tables list every possible input combination and the corresponding output. Here is the truth table for a two-input AND gate:
真值表列出了每种可能的输入组合及其对应的输出。以下是二输入 AND 门的真值表：
| Input A | Input B | Output (A AND B) |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
Other common gates include NAND (NOT AND), NOR (NOT OR), and XOR (exclusive OR). XOR outputs 1 only when the inputs are different.
其他常见门包括 NAND（与非）、NOR（或非）和 XOR（异或）。XOR 仅在输入不同时输出 1。
5. Memory and Storage | 存储器与存储设备
Primary memory, also known as main memory, is directly accessible by the CPU. It includes RAM (Random Access Memory) and ROM (Read Only Memory). RAM is volatile – its contents are lost when the computer is turned off – while ROM is non-volatile and stores the boot instructions (BIOS/UEFI).
主存储器（也称内存）可直接由 CPU 访问。它包括 RAM（随机存取存储器）和 ROM（只读存储器）。RAM 是易失性的——计算机关闭后其中内容会丢失——而 ROM 是非易失性的，存储启动指令（BIOS/UEFI）。
Secondary storage holds data permanently. Common types include magnetic hard disk drives (HDD), solid-state drives (SSD), and optical discs (CD, DVD). USB flash drives and SD cards use flash memory, which is fast and durable.
辅助存储器永久保存数据。常见类型包括机械硬盘 (HDD)、固态硬盘 (SSD) 和光盘（CD、DVD）。U 盘和 SD 卡使用闪存，速度快且耐用。
Data storage units scale from bits to bytes, kilobytes, megabytes, gigabytes and beyond. The table below shows the relationship between these units:
数据存储单位从位到字节、千字节、兆字节、吉字节等逐级递进。下表显示了这些单位之间的关系：
| Unit | Equivalent |
|---|---|
| 1 bit | Smallest unit of data (0 or 1) |
| 1 byte (B) | 8 bits |
| 1 kilobyte (KB) | 1024 bytes |
| 1 megabyte (MB) | 1024 KB |
| 1 gigabyte (GB) | 1024 MB |
| 1 terabyte (TB) | 1024 GB |
6. Networks and the Internet | 网络与互联网
A computer network is a group of connected devices that can share resources and communicate. Networks can be classified by size: PAN (Personal Area Network), LAN (Local Area Network), and WAN (Wide Area Network). The internet is a global WAN connecting millions of networks.
计算机网络是一组可共享资源并通信的连接设备。网络可按规模分类：PAN（个人局域网）、LAN（局域网）和 WAN（广域网）。互联网是连接数百万网络的全球 WAN。
Common network hardware includes routers, switches, hubs, and modems. A router directs data packets between networks, while a switch connects devices within a LAN and forwards data to the correct destination.
常见的网络硬件包括路由器、交换机、集线器和调制解调器。路由器在网络间引导数据包，而交换机则在局域网内连接设备并将数据转发到正确的目的地。
Network topologies describe the physical or logical layout. The star topology connects all devices to a central switch; the bus topology uses a single backbone cable; a mesh topology has multiple redundant connections for reliability.
网络拓扑描述了物理或逻辑布局。星型拓扑将所有设备连接到一个中央交换机；总线拓扑使用单一主干电缆；网状拓扑拥有多条冗余连接以提高可靠性。
Protocols are sets of rules that govern data transmission. TCP/IP is the fundamental suite for the internet. HTTP/HTTPS is used for web pages, FTP for file transfers, and SMTP for email.
协议是管理数据传输的规则集。TCP/IP 是互联网的基础协议族。HTTP/HTTPS 用于网页浏览，FTP 用于文件传输，SMTP 用于电子邮件。
7. Cybersecurity and Safe Practices | 网络安全与安全实践
Cybersecurity protects systems, networks, and data from digital attacks. Common threats include malware (viruses, worms, ransomware), phishing, and brute-force attacks. Malware can damage files, steal data, or lock you out of your device.
网络安全旨在保护系统、网络和数据免受数字攻击。常见威胁包括恶意软件（病毒、蠕虫、勒索软件）、网络钓鱼和暴力破解攻击。恶意软件可能损坏文件、窃取数据或将你锁在设备之外。
Phishing involves tricking users into revealing sensitive information, often through fake emails or websites that look legitimate. Always check the sender's address and avoid clicking suspicious links.
网络钓鱼是通过欺骗手段诱使用户泄露敏感信息，往往通过看似合法的虚假邮件或网站实现。务必检查发件人地址，切勿点击可疑链接。
To stay safe, use strong passwords (a mix of letters, numbers and symbols), enable two-factor authentication, and keep software updated. Installing antivirus and firewall protection adds extra layers of defence.
为了保持安全，应使用强密码（字母、数字和符号的组合）、启用双因素认证并保持软件更新。安装防病毒软件和防火墙可以增加额外的防御层。
Ethical issues include respecting privacy, avoiding plagiarism, and understanding the impact of digital footprints. Always cite sources and obtain permission before using someone else's work.
伦理问题包括尊重隐私、避免剽窃，并了解数字足迹的影响。始终注明出处，并在使用他人作品前获得许可。
8. Programming Basics: Algorithms and Flowcharts | 编程基础：算法与流程图
An algorithm is a step-by-step procedure to solve a problem. It must be unambiguous, finite, and effective. Pseudocode is a way to describe algorithms using plain English combined with programming-like structures.
算法是解决问题的一步一步的过程。它必须明确、有限且有效。伪代码是一种使用简单英语结合类编程结构来描述算法的方法。
Flowcharts represent algorithms graphically using standard symbols: ovals for start/end, parallelograms for input/output, rectangles for processes, and diamonds for decisions. Arrows show the flow of control.
流程图使用标准符号以图形方式表示算法：椭圆形表示开始/结束，平行四边形表示输入/输出，矩形表示处理，菱形表示判断。箭头表示控制流程。
A simple algorithm to find the larger of two numbers could be expressed as:
一个找出两个数中较大值的简单算法可以表示为：
INPUT num1, num2
IF num1 > num2 THEN
OUTPUT num1
ELSE
OUTPUT num2
ENDIF
In a flowchart, this would involve an input symbol, a decision diamond comparing the two numbers, and output symbols following the True and False branches.
在流程图中，这将涉及一个输入符号、一个比较两个数字的决策菱形，以及沿着“真”和“假”分支的输出符号。
9. Programming Concepts: Variables, Data Types & Control Structures | 编程概念：变量、数据类型与控制结构
Variables are named storage locations in memory that hold values which can change during program execution. Common data types include integer, real (float), string, character, and Boolean.
变量是内存中命名的存储位置，保存可在程序执行期间更改的值。常见数据类型包括整型、实型（浮点型）、字符串、字符和布尔型。
Control structures determine the order in which statements are executed. Sequence runs one instruction after another. Selection (if-else) makes decisions based on conditions. Iteration (loops) repeats a block of code: FOR loops are used when the number of repetitions is known; WHILE loops repeat while a condition remains true.
控制结构决定语句的执行顺序。顺序结构按顺序执行每条指令。选择结构（if-else）根据条件做出决策。迭代结构（循环）重复执行代码块：FOR 循环用于已知重复次数的情况；WHILE 循环在条件为真时重复执行。
Indentation is crucial in languages like Python to define blocks of code. Clear, meaningful variable names and comments make code easier to read and debug.
在 Python 等语言中，缩进对于定义代码块至关重要。清晰、有意义的变量名和注释使代码更易于阅读和调试。
10. Sorting and Searching Algorithms | 排序与搜索算法
Algorithms are evaluated by their efficiency, often in terms of the number of comparisons or swaps required. Two fundamental types are sorting and searching.
算法通过其效率来评估，通常依据所需的比较次数或交换次数。两种基本类型是排序和搜索。
Bubble sort repeatedly steps through the list, comparing adjacent items and swapping them if they are in the wrong order. It is simple but inefficient for large lists. Here is a pseudocode outline:
冒泡排序重复遍历列表，比较相邻项并在顺序错误时交换它们。它很简单，但对于大型列表效率低下。以下是伪代码框架：
FOR i FROM 0 TO n-1
FOR j FROM 0 TO n-i-1
IF list[j] > list[j+1] THEN
SWAP list[j] and list[j+1]
ENDIF
ENDFOR
ENDFOR
Binary search is an efficient algorithm to find an item in a sorted list. It compares the target value to the middle element, discarding half of the list each time until the item is found or the search interval is empty.
二分搜索是一种在已排序列表中查找项目的高效算法。它将目标值与中间元素进行比较，每次丢弃一半列表，直到找到该项目或搜索区间为空。
Linear search simply checks each element one by one. It works on unsorted data but is slower for large datasets.
线性搜索只是逐个检查每个元素。它适用于未排序的数据，但对于大数据集来说速度较慢。
Understanding how these algorithms work helps you choose the right one for a given problem and write more efficient code.
理解这些算法的工作原理有助于你为特定问题选择合适的算法，并编写更高效的代码。
Published by TutorHao | Computing Revision Series | aleveler.com
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