Advanced level 2026 South West mock Computer science 2

I have extracted the text and data from your newest image, which covers Memory Hierarchy, Digital Logic (Full Adders), Data Representation, and Operating System Scheduling.

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COMPUTER SCIENCE EXAMINATION SECTION

1. (i)

• a) A particular computer has $2048 \text{ MB}$ of byte-addressable main memory. How many bus lines are required to uniquely address every location of this memory? (2 marks)

• b) How does cache memory improve CPU performance? (2 marks)

• c) Describe the memory hierarchy that might exist in a typical digital computer. (3 marks)

(ii)

• a) Construct a truth table for the addition of three binary digits A, B, and C. (4 marks)

• b) Write the Boolean expressions for the Sum and Carry outputs of a full adder. (3 marks)

• c) Draw a block diagram of a 3-bit parallel adder, using an appropriate combination of half-adders and full-adders. Clearly label all inputs, outputs, and carry connections. (3 marks)

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2. (i)

• a) Add $-50_{10}$ and $97_{10}$ in 8-bit two’s complement. (3 marks)

• b) Subtract $35_8$ from $24_8$ in 6-bit sign absolute. (3 marks)

• c) Convert the 8-bit signed two’s complement hexadecimal number $A7$ to decimal. (3 marks)

(ii)

• a) Briefly describe the function of each of the components of a machine instruction. (3 marks)

• b) Distinguish between immediate addressing and absolute addressing. (2 marks)

• c) For each of the following applications, identify the most appropriate addressing mode. Write only the number that corresponds to an application statement and then state the addressing mode. (3 marks)

Application	Addressing Mode
1. Used for dynamic data access such as linked lists
2. Used for fast arithmetic and logic operations
3. Used to access fixed memory locations such as global variables

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3. (i)

• a) Explain the term scheduling as used in operating systems. (1 mark)

• b) Describe two operating system components that are responsible for process scheduling. (4 marks)

• c) State three events that can cause a scheduling decision to take place. (3 marks)

(ii) Consider a set of process P1, P2, P3, and P4, with their respective arrival times and burst times given in the table below. In this system, context switch time is 1 millisecond.

Process ID	Arrival Time	Burst Time
P1	0	8
P2	3	5
P3	4	3
P4	5	2

• a) Explain what is meant by context switch time. (1 mark)

• b) Draw a Gantt chart for this system using Round Robin scheduling with a time quantum of $3 \text{ milliseconds}$. (3 marks)

• c) Calculate the average turnaround time, average waiting time, and percentage CPU utilization time for these processes. (5 marks)

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Would you like me to calculate the bus lines for the $2048 \text{ MB}$ memory or walk through the Round Robin Gantt chart for those four processes?