Advanced level 2026 Centre mock computer science 2

I have extracted the text and data from your most recent image, which focuses on binary data representation (two’s complement and floating-point normalization) and assembly-level addressing modes.

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COMPUTER SCIENCE EXAMINATION SECTION

1. (i) A computer uses two bytes to store a number as shown below:

(Byte 1)

| 1 | 0 | 1 | 1 | 0 | 1 | 0 | 1 |

| :— | :— | :— | :— | :— | :— | :— | :— |

(Byte 2)

| 0 | 0 | 1 | 1 | 0 | 1 | 1 | 0 |

• (a) Convert Byte 1 and Byte 2 into decimal if each byte represents a two’s complement integer value. (3 marks)

• (b) Consider the second byte to be a floating point number with the first 5 MSB representing the Mantissa and the remaining 3 bits representing the exponent:

  • Give a reason why the floating point number is not NORMALIZED. (1 mark)

  • Normalize the floating point number and give its denary equivalent. (3 marks)

• (c) What effect will increasing the number of bits allocated to the mantissa have on the representation of real numbers? (1 mark)

• (d) What effect will decreasing the number of bits allocated to the exponent have on the representation of real numbers? (1 mark)

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(ii) The figure below shows the content of a memory and that of an Index Register R1. Consider the code snippet below and answer the questions that follow.

Memory Table:

| Address | Content |

| :— | :— |

| 800 | 900 |

| 900 | 1000 |

| 1000 | 500 |

| 1100 | 600 |

| 1600 | 700 |

Register R1: 800

Code Snippet:

1. LOAD 900 // Immediate addressing mode

2. ADD [800] // Direct Addressing mode

3. SUB [[900]] // Indirect Addressing mode

4. ADD [800 + R1] // Index Addressing mode

• (a) Define the following terms: Addressing mode and Instruction format. (2 marks)

• (b) Which instruction set architecture is used in the code snippet above? Describe the architecture. (2 marks)

• (c) Considering that the nature of the addressing mode described in the above code snippet is of obvious meaning, dry-run the code and determine the content of the accumulator after executing all the instructions. (4 marks)

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Would you like me to walk through the dry-run for the accumulator calculation in 1(ii)(c) or explain the rules for floating-point normalization in 1(i)(b)?