📚 Year 9 WJEC Computer Science: Unit Test Mock Exam Walkthrough | Year 9 WJEC 计算机：单元测试模拟卷解析
This walkthrough covers the key topics you might face in a Year 9 WJEC Computer Science unit test. By reviewing each question type and its solution, you will strengthen your understanding of hardware, data representation, algorithms, programming basics and more. The explanations are designed to help you avoid common mistakes and build confidence for your actual exam.
本解析涵盖了 Year 9 WJEC 计算机科学单元测试中可能出现的关键主题。通过回顾每类题型及其解答，你将加深对硬件、数据表示、算法、程序设计基础等内容的理解。这些讲解旨在帮助你避免常见错误，并为正式考试树立信心。
1. Computer Hardware Fundamentals | 计算机硬件基础
A typical question asks you to identify the main functions of the central processing unit (CPU). The CPU is often called the ‘brain’ of the computer because it carries out the fetch–decode–execute cycle. It fetches instructions from memory, decodes them to understand what action is needed, and then executes them. The CPU contains the arithmetic logic unit (ALU) for calculations and logical operations, the control unit (CU) that directs data flow, and registers that hold small amounts of data temporarily.
常见题目要求你说明中央处理器（CPU）的主要功能。CPU 常被称为计算机的 ‘大脑’，因为它执行取指–译码–执行周期。它从内存中取出指令，进行译码以理解需要执行什么操作，然后执行这些指令。CPU 内部包含进行算术和逻辑运算的算术逻辑单元（ALU）、指挥数据流的控制单元（CU）以及临时存放少量数据的寄存器。
For example, you might be asked: ‘Explain the role of the ALU.’ A good answer would state that the ALU performs arithmetic operations (like addition and subtraction) and logical operations (such as AND, OR, NOT). It receives data from the registers and sends the result back to memory or to an output device.
例如，你可能被问到：’解释 ALU 的作用。’ 一份好的答案会说明 ALU 执行算术运算（如加法和减法）和逻辑运算（如与、或、非）。它从寄存器接收数据，并将结果送回内存或输出设备。
2. Input and Output Devices | 输入与输出设备
Questions on peripheral devices test your ability to distinguish between input and output. An input device sends data to the computer; an output device receives data from the computer. Common mistakes include confusing a touchscreen (which is both an input and output device) or categorising a speaker as input.
关于外围设备的题目考察你区分输入与输出的能力。输入设备将数据发送给计算机；输出设备从计算机接收数据。常见错误包括混淆触摸屏（它既是输入设备也是输出设备）或将扬声器归类为输入设备。
A mock question might ask: ‘Give two examples of input devices and explain their use.’ Good answers include: a keyboard (used to enter text and commands) and a microphone (used to capture audio). Another variant could ask you to name an output device used for displaying visual information—the monitor. You should also be able to explain why a printer is an output device because it receives processed data and produces a physical copy.
模拟题可能会问：’举出两个输入设备的例子并说明其用途。’ 好的答案包括：键盘（用于输入文本和命令）和麦克风（用于采集音频）。另一种形式可能要求你说出一种用于显示视觉信息的输出设备——显示器。你还应该能够解释为什么打印机是输出设备，因为它接收处理后的数据并生成物理副本。
3. Primary and Secondary Storage | 主存储与辅助存储
You need to know the difference between RAM and ROM. RAM (Random Access Memory) is volatile, meaning it loses its data when the power is turned off; it holds the programs and data currently in use. ROM (Read Only Memory) is non-volatile and stores the boot-up instructions (firmware) that do not change. A test might include a table where you fill in whether a given statement applies to RAM, ROM, or both.
你需要了解 RAM 和 ROM 的区别。RAM（随机存取存储器）是易失性的，意味着断电时数据会丢失；它保存当前正在使用的程序和数据。ROM（只读存储器）是非易失性的，存储不会改变的引导指令（固件）。考试中可能会出现一个表格，要求你填写某个说法适用于 RAM、ROM 还是两者。
Secondary storage devices are non‑volatile and include magnetic (hard disk), solid‑state (SSD, USB flash drive) and optical (CD, DVD). A classic question compares magnetic and solid‑state storage: magnetic drives have moving parts, can be slower and are easily damaged by movement, whereas SSDs have no moving parts, are faster, but often cost more per gigabyte. You may also be asked to justify the choice of storage for backing up a school network—capacity and reliability are key factors.
辅助存储设备是非易失性的，包括磁介质（硬盘）、固态介质（SSD、U盘）和光学介质（CD、DVD）。一道经典题目会比较磁介质和固态存储：磁介质驱动器有活动部件，速度较慢且容易因移动而损坏，而固态硬盘没有活动部件、速度更快，但每 GB 的成本通常更高。你也可能被问到为学校网络备份选择存储介质的理由——容量和可靠性是关键因素。
4. Binary and Denary Conversion | 二进制与十进制转换
Understanding binary is essential. You will often be asked to convert an 8‑bit binary number to denary (base 10) or vice versa. For example, convert the binary number 01101001 to denary. The place values from left to right are 128, 64, 32, 16, 8, 4, 2, 1. The number 01101001 has ones at the 64, 32, 8, and 1 positions: 64 + 32 + 8 + 1 = 105. So the denary value is 105.
理解二进制是基础。你经常会被要求将一个 8 位二进制数转换为十进制，或反过来。例如，将二进制数 01101001 转换为十进制。从右向左的位值依次是 128、64、32、16、8、4、2、1。数字 01101001 在 64、32、8 和 1 的位置上有1：64 + 32 + 8 + 1 = 105。因此十进制值是 105。
To convert from denary to binary, use repeated division by 2. For instance, convert 78 to binary. 78 ÷ 2 = 39 remainder 0; 39 ÷ 2 = 19 remainder 1; 19 ÷ 2 = 9 remainder 1; 9 ÷ 2 = 4 remainder 1; 4 ÷ 2 = 2 remainder 0; 2 ÷ 2 = 1 remainder 0; 1 ÷ 2 = 0 remainder 1. Reading the remainders from bottom to top gives 1001110, but as an 8‑bit byte you pad with a leading zero: 01001110.
从十进制转换为二进制，使用除 2 取余法。例如，将 78 转换为二进制。78 ÷ 2 = 39 余 0；39 ÷ 2 = 19 余 1；19 ÷ 2 = 9 余 1；9 ÷ 2 = 4 余 1；4 ÷ 2 = 2 余 0；2 ÷ 2 = 1 余 0；1 ÷ 2 = 0 余 1。从下往上读取余数得到 1001110，但作为 8 位字节，前面补零得到 01001110。
5. Binary Addition | 二进制加法
Binary addition follows simple rules: 0 + 0 = 0; 0 + 1 = 1; 1 + 0 = 1; 1 + 1 = 0, carry 1 to the next column; 1 + 1 + 1 (carry in) = 1, carry 1. A common exam task gives two binary numbers and asks for the sum. Example: Add 0101 (5) and 0011 (3).
二进制加法遵循简单规则：0 + 0 = 0；0 + 1 = 1；1 + 0 = 1；1 + 1 = 0，并向下一位进 1；1 + 1 + 1（进位）= 1，并进 1。常见的考试任务是给出两个二进制数并求和。例如：计算 0101（5）与 0011（3）的和。
0101
+ 0011
——
1000
The result is 1000, which is 8 in denary. If there is a carry beyond the leftmost column into a ninth bit, this is called an overflow, and the answer may not fit in 8 bits. You might be asked to recognise an overflow situation and explain why it occurs.
结果为 1000，即十进制中的 8。如果最左边的一列产生进位到第9位，这称为溢出，答案可能无法容纳在 8 位内。你可能会被要求识别溢出情况并解释原因。
6. Logic Gates and Truth Tables | 逻辑门与真值表
Logic gates form the building blocks of digital circuits. Year 9 WJEC typically covers AND, OR and NOT gates. An AND gate outputs 1 only if both inputs are 1. An OR gate outputs 1 if at least one input is 1. A NOT gate simply inverts the input.
逻辑门构成数字电路的基本构件。Year 9 WJEC 通常涵盖与门（AND）、或门（OR）和非门（NOT）。与门仅在两个输入都为 1 时输出 1。或门在至少一个输入为 1 时输出 1。非门直接反转输入。
You should be able to draw truth tables and complete missing values. For a two‑input AND gate:
| Input A | Input B | Output |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
Be ready to combine gates. For instance, the expression NOT (A AND B) is a NAND gate. Its truth table is the exact inverse of AND. Questions may also ask you to identify a logic gate from a diagram or to write a Boolean expression.
准备好组合逻辑门。例如，表达式 NOT (A AND B) 是与非门。其真值表恰为与门的反转。题目也可能要求你从电路图中识别逻辑门或写出布尔表达式。
7. Algorithms and Flowchart Symbols | 算法与流程图符号
An algorithm is a step‑by‑step set of instructions to solve a problem. You need to know standard flowchart symbols: oval for start/stop, parallelogram for input/output, rectangle for a process, diamond for a decision, and arrows for flow direction. A typical question might ask you to draw a flowchart for making a cup of tea or to interpret a given flowchart and state the final output.
算法是解决一个问题的一组逐步指令。你需要了解标准流程图符号：椭圆形表示开始/结束，平行四边形表示输入/输出，矩形表示处理步骤，菱形表示判断，箭头表示流程方向。典型题目可能会要求你绘制一个泡茶的流程图，或者解读给定的流程图并给出最终输出。
For example, a flowchart might start with inputting a number N. A decision diamond then checks if N > 10. If yes, it outputs ‘High’, otherwise it outputs ‘Low’. You should trace through with an example value and give the expected output. You might also need to spot an error in a flowchart, such as a missing stop symbol or an infinite loop where the decision never changes the flow to an exit.
例如，某个流程图以输入数字 N 开始。一个判断菱形检查 N 是否大于 10。如果是，输出 ‘High’，否则输出 ‘Low’。你应该用示例值进行追踪并给出预期输出。你可能还需要找出流程图中的错误，例如缺少停止符号，或者判断永远无法使流程进入出口而导致的无限循环。
8. Introduction to Python Programming | Python 程序设计入门
WJEC often introduces basic Python in Year 9. You can expect a question asking you to write a short program using input(), print(), variables, and conditional statements. For instance: ‘Write a program that asks for the user’s age and prints “You can vote” if the age is 18 or over, otherwise prints “Too young to vote”.’ A model solution looks like:
WJEC 通常在 Year 9 引入基础 Python。题目可能会要求你使用 input()、print()、变量和条件语句编写一个简短程序。例如：’编写一个程序，询问用户的年龄，如果年龄在 18 岁或以上，打印 “You can vote”，否则打印 “Too young to vote”。’ 参考解法如下：
age = int(input(“Enter your age: “))
if age >= 18:
print(“You can vote”)
else:
print(“Too young to vote”)
Pay attention to indentation—Python uses indentation to define code blocks. A missing colon or incorrect indentation will generate a syntax error. You should also know how to convert input (which is always a string) into an integer using int() or a float using float() when numerical comparisons are needed.
注意缩进——Python 使用缩进来定义代码块。缺少冒号或缩进错误会产生语法错误。你还应该知道，当需要进行数值比较时，如何使用 int() 将输入（始终是字符串）转换为整数，或使用 float() 转换为浮点数。
9. Data Types, Variables and Operators | 数据类型、变量与运算符
Understanding data types helps you debug programs. Python’s basic data types include integer (int), float, string (str) and Boolean (bool). A variable is a named storage location; its type is determined by the value you assign. For example, after score = 42, score is an int. After name = “Alice”, name is a str.
理解数据类型有助于你调试程序。Python 的基本数据类型包括整数（int）、浮点数（float）、字符串（str）和布尔值（bool）。变量是一个命名的存储位置；其类型由你赋给的值决定。例如，执行 score = 42 后，score 是整型。执行 name = “Alice” 后，name 是字符串型。
Arithmetic operators are used for calculations: + (addition), – (subtraction), * (multiplication), / (division), // (integer division), % (modulus) and ** (exponentiation). A typical question might ask for the result of 15 % 4 (remainder of 15 ÷ 4), which is 3. You could also see a question about operator precedence, for instance 2 + 3 * 4 evaluates to 14, not 20, because multiplication has higher precedence.
算术运算符用于计算：+（加）、-（减）、*（乘）、/（除）、//（整除）、%（取模）和**（乘方）。典型题目可能会问 15 % 4 的结果（15 ÷ 4 的余数），答案是 3。你还可能遇到关于运算符优先级的问题，例如 2 + 3 * 4 的结果是 14 而不是 20，因为乘法的优先级更高。
10. Internet, Networks and Cybersecurity | 互联网、网络与网络安全
Network basics include understanding the difference between a LAN (Local Area Network) and a WAN (Wide Area Network). A LAN covers a small geographical area, like a school building, while a WAN connects networks across cities or countries. You should know that network hardware includes switches, routers, and network interface cards. A router directs data packets between different networks, often connecting a home network to the Internet.
网络基础知识包括理解 LAN（局域网）和 WAN（广域网）的区别。LAN 覆盖较小的地理区域，如学校大楼，而 WAN 连接跨越城市或国家的网络。你应该知道网络硬件包括交换机、路由器和网络接口卡。路由器在不同网络之间导引数据包，通常将家庭网络连接到互联网。
Cybersecurity questions often focus on threats like malware, phishing, and brute‑force attacks. Malware is malicious software that can damage or disrupt systems; phishing tricks users into revealing personal information by pretending to be a trustworthy entity. A strong password uses a mix of upper‑ and lower‑case letters, numbers and symbols. You might be asked to explain two ways to protect against phishing: being suspicious of unexpected emails and checking the sender’s address carefully.
网络安全题目通常关注恶意软件（malware）、网络钓鱼（phishing）和暴力攻击（brute‑force attacks）等威胁。恶意软件是可以破坏或扰乱系统的恶意的软件；网络钓鱼通过伪装成可信实体，诱骗用户泄露个人信息。一个强密码应包含大小写字母、数字和符号的组合。你可能会被要求解释两种防范网络钓鱼的方法：对意外邮件保持警惕，并仔细检查发件人地址。
11. Computational Thinking and Decomposition | 计算思维与问题分解
Computational thinking involves breaking down a complex problem into smaller, more manageable parts—this is called decomposition. Another element is pattern recognition: spotting similarities between problems to reuse solutions. Abstraction involves focusing on the important information only, ignoring irrelevant detail. A typical question gives a scenario, like planning a school trip, and asks you to explain how decomposition could help. You might state that the problem can be split into transport, cost, permissions, and scheduling, making it easier to solve each part.
计算思维包括将一个复杂问题拆分成更小、更易于处理的部分——这称为分解。另一个要素是模式识别：发现不同问题之间的相似处，以便重用解决方案。抽象则是指只关注重要信息，忽略不必要的细节。典型题目会给出一个场景，如策划学校旅行，并询问分解如何帮助解决。你可能会说明问题可以拆分为交通、费用、许可和日程安排等部分，从而使每个部分更容易解决。
Be prepared to apply computational thinking to a simple programming task. For instance, designing a program to convert miles to kilometres requires you to identify the input (miles), the process (multiply by 1.609), and the output (kilometres). This step‑by‑step plan is an algorithm developed through decomposition.
准备好将计算思维应用于简单的编程任务。例如，设计一个将英里转换为公里的程序，需要你识别输入（英里）、处理（乘以 1.609）和输出（公里）。这个逐步计划就是通过分解开发出的算法。
12. Reviewing Common Mistakes and Exam Tips | 回顾常见错误与考试技巧
Many marks are lost by not reading the question carefully. For example, a question that says ‘State and explain two reasons…’ expects a statement and then an explanation for each. Only giving the reasons without explanation limits your marks. Another frequent error is confusing memory units: remember that 1 byte = 8 bits, 1 kilobyte ≈ 1000 bytes, and the unit for a character is typically 1 byte (in ASCII).
很多失分是由于没有仔细审题。例如，一道题说 ‘陈述并解释两个原因……’，就需要先给出陈述，然后各自加以解释。只给出原因而不作解释会限制你的得分。另一个常见错误是混淆存储单位：记住 1 字节 = 8 位，1 千字节 ≈ 1000 字节，一个字符通常占 1 字节（在 ASCII 码中）。
When writing code in a paper‑based exam, always double‑check your syntax. A missing parenthesis or colon can make the whole answer incorrect. Similarly, in binary calculations, neatly align columns to avoid misreading place values. If you finish early, use spare time to check logic gates truth tables and to trace your flowcharts once more with different data.
在笔试中书写代码时，务必仔细检查语法。少一个括号或冒号可能导致整个答案错误。同样，在进行二进制计算时，对齐数位能避免位值读错。如果你提前完成，用剩余时间检查逻辑门真值表，并用不同数据再追踪一次流程图。
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