Year 9 WJEC Computer Science: Unit Test Mock Paper Analysis | WJEC 九年级计算机科学单元测试模拟卷解析

📚 Year 9 WJEC Computer Science: Unit Test Mock Paper Analysis | WJEC 九年级计算机科学单元测试模拟卷解析

Mock examinations are an essential part of preparing for the WJEC Computer Science assessments in Year 9. This analysis walks through a typical unit test paper, explaining key concepts and common pitfalls in both English and Chinese to boost your understanding and confidence.

模拟考试是准备WJEC九年级计算机科学评估的重要组成部分。本文解析一张典型的单元测试卷，用中英文解释关键概念和常见错误，以加深你的理解并提升自信。

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1. Binary to Denary Conversion | 二进制转十进制

Question: Convert the binary number 101101 into denary (decimal). [2 marks]

For 101101, we have 1×2⁵ + 0×2⁴ + 1×2³ + 1×2² + 0×2¹ + 1×2⁰ = 32 + 0 + 8 + 4 + 0 + 1 = 45.

在二进制中，每一位代表2的幂，从最右边的2⁰开始。对于101101，计算为1×2⁵ + 0×2⁴ + 1×2³ + 1×2² + 0×2¹ + 1×2⁰ = 32 + 0 + 8 + 4 + 0 + 1 = 45。

Always check your place values: 32, 16, 8, 4, 2, 1. A common mistake is forgetting that the rightmost bit is the least significant bit (2⁰), not 2¹.

请务必核对位权值：32, 16, 8, 4, 2, 1。常见错误是忘记最右边的位是最低有效位(2⁰)，而不是2¹。

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2. Data Storage Units | 数据存储单位

Question: How many bytes are there in 3 Kilobytes (KB)? [1 mark]

ecause digital systems are based on powers of two. Therefore 3 KB = 3 × 1024 = 3072 bytes.

计算机中的千字节(KB)通常为1024字节，因为数字系统基于2的幂。因此3 KB = 3 × 1024 = 3072字节。

Remember the ascending order: bit, nibble (4 bits), byte (8 bits), kilobyte (1024 bytes), megabyte, gigabyte, etc. In exams, always use 1024 as the multiplier, not 1000, unless explicitly told otherwise.

记住递增顺序：位、半字节(4位)、字节(8位)、千字节(1024字节)、兆字节、吉字节等。考试中始终以1024为乘数，除非题目明确说明用1000。

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3. CPU Components | 中央处理器组件

Question: Name two main components of the CPU and briefly describe their functions. [4 marks]

Control Unit (CU) directs the flow of data and instructions, fetches and decodes instructions, and controls other parts of the CPU like the ALU and registers. Arithmetic Logic Unit (ALU) performs all arithmetic calculations (addition, subtraction) and logical operations (AND, OR, NOT).

控制单元(CU)指导数据和指令的流动，提取并解码指令，并控制CPU的其他部分如ALU和寄存器。算术逻辑单元(ALU)执行所有算术计算（加、减）和逻辑操作（与、或、非）。

Many students confuse the CU with the ALU. A helpful tip: CU is the 'manager' that coordinates, ALU is the 'worker' that does calculations. Also acceptable is mentioning registers such as the Program Counter (PC) or Accumulator.

许多学生混淆CU和ALU。一个提示：CU是协调的“经理”，ALU是计算的“工人”。提及程序计数器(PC)或累加器等寄存器也是可接受的答案。

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4. Logic Gates and Truth Tables | 逻辑门与真值表

Question: Complete the truth table for a 2-input OR gate. [3 marks]

A	B	Output (A OR B)
0	0	0
0	1	1
1	0	1
1	1	1

An OR gate gives output 1 when at least one of its inputs is 1. Only when both inputs are 0 does the output become 0. This is the logical sum operation, symbolised as A + B in boolean algebra.

当至少一个输入为1时，或门输出1。只有两个输入均为0时，输出才为0。这是逻辑和运算，在布尔代数中用A + B表示。

table for AND, OR and NOT. Remember: AND = both inputs must be 1; NOT = inverts the input.

考试中可能会要求你绘制门符号或完成与门、或门和非门的真值表。记住：与门要求两个输入均为1；非门将输入取反。

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5. Flowchart Interpretation | 流程图解读

Question: A flowchart takes an input number, doubles it repeatedly while the number is less than or equal to 100, then outputs the final number. If the input is 7, what is the output? [2 marks]

28 × 2 = 56, 56 × 2 = 112. Now 112 is greater than 100, so the loop stops. Output is 112.

从7开始：7 × 2 = 14, 14 × 2 = 28, 28 × 2 = 56, 56 × 2 = 112。此时112 > 100，循环停止。输出为112。

Flowcharts use diamond shapes for decisions and rectangles for processes. This tests understanding of condition-controlled iteration. Trace table practice helps avoid off-by-one errors.

流程图用菱形表示判断，矩形表示处理。这考查对条件控制迭代的理解。通过追踪表练习有助于避免差一错误。

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6. Programming Basics: IF Statements and Loops | 编程基础：条件语句与循环

Question: Write pseudocode to output all even numbers from 2 to 20 inclusive. [4 marks]

A clean solution uses a FOR loop: FOR i ← 2 TO 20 STEP 2; OUTPUT i; NEXT i. The STEP 2 ensures only even numbers are printed without needing an IF condition.

一种清晰的方案使用FOR循环：FOR i ← 2 TO 20 STEP 2; 输出 i; NEXT i。STEP 2确保只打印偶数，无需IF条件。

An alternative WHILE loop: number ← 2; WHILE number ≤ 20 DO OUTPUT number; number ← orrectly. Remember pseudocode does not have strict syntax, but it must be logically clear.

另一种WHILE循环：number ← 2; 当

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