Advanced level 2025 South West Regional Mock computer science 2
Advanced level 2025 South West Regional Mock computer science 2
(i) A computer uses two bytes to store a number as shown below.
(a) Convert Byte 1 and Byte 2 into decimal if each byte represents a one’s complement integer value?
(3 marks)
(b) Convert the bit pattern above into decimal if it represents a floating-point number with Byte 1 as the
mantissa and Byte 2 as the exponent, both in two’s complement. (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)
(ii) (a) A programmer has written a code snippet that includes the instruction below. In this context, Rx
denotes a processor register and #n denotes a denary number.
LOAD R0, #100
Explain the term addressing mode and then identify the addressing mode used in this instruction.
(2 marks)
(b) Write an assembly language code snippet to execute the expression “C = A + B” using two-address
instructions only. (4 marks)
(c) Suggest two possible advantages of programming in assembly language rather than in high-level
language. (2 marks)
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2. (i) (a) Describe two characteristics of solid-state storage that make them more suitable for laptop computers
than magnetic storage. (4 marks)
(b) How many times greater is the capacity of a 17 GB double-sided DVD than that of a 700 MB CD?
(2 marks)
(ii) (a) Construct a truth table for the Boolean expression ̅ ̅ ̅. (4 marks)
(b) From the truth table in (a) above or otherwise, show that A . (3 marks
