Advanced level 2024 South regional mock computer science 2
Advanced level 2024 South regional mock computer science 2
1. i) a) Perform the following operation using 8-bit 2’s complement arithmetic
(3 Marks)
b) Consider the figure below. The half adder (HA) and Half subtractor (HS) are
represented using block diagrams. Write the simplified Boolean expressions for
DIFFERENCE and BORROW outputs in the figure below. (4 Marks)
.
ii) a) Determine the number of address lines and the number of bytes that can be
stored in the specified memory 4G x 64 (2 Marks)
b) Explain briefly why the DRAM loses its content if not constantly refreshed. (2 Marks)
iii) a) Describe three characteristics of a CPU that can affect the overall
performance of a computer. (3 Marks)
b) A computer has 32-bit instructions and 12-bit addresses. If there are already
250 two-address instructions, how many one-address instructions can be
formulated? (3 Marks)
2. i) The machine instruction cycle is the process by which a program instruction is fetched,
decoded, executed and the results are stored.
a) Explain the fetch phase of the machine instruction cycle using the register
transfer notation. (3 Marks)
b) Describe the roles played by different buses in the machine instruction cycle. (3 Marks)
ii) a) A digital circuit receives a 4-bit input, , , , ) and produces
2-bit output, , ) indicating the most significant bit of the input that is TRUE.
For example, if the input is 0010, the output Y should be 01 that is is 0 and is 1.
Ignore the case where all the inputs are FALSE.
Give a simplified Boolean equation for each output. (4 Marks)
b) An instruction is stored at location 300 with its address field at location 301.
The address field has the value 400. A processor register R1 contains the number 200.
Evaluate the effective address if the addressing mode of the instruction is direct;
immediate; relative; register indirect; and index with R1 as the index register. (5 Marks)
iii) Describe the stored program concept in Von-Neumann machine architecture (2 Marks)
3. i) Memory management is one of the functions of an operating system. Part of a computer’s
memory is represented below.
The operating system divides the memory into equally sized chunks.
a) State the name of the type of memory management used. (1 Mark)
b) The operating system needs to load program C into memory but there is not enough space.
Describe how the operating system would use virtual memory to load program C. (3 Marks)
c) State one disadvantage of using this type of memory management.
BY AHMED FALLY
