Advanced level 2025 South regional mock computer science 2
Advanced level 2025 South regional mock computer science 2
1- An 8bits single core computer has a RAM size of 32 KB with no cache
memory and a 16bit address bus.
| i) ii) |
Calculate the maximum size of the main memory ““ Explain each of the four characteristic highlighted in the problem specification above and explain how it can affect the computer performance. |
[1mark] |
| [2marks x 4 = 8marks] | ||
| iii) | The integer -79 is to be stored in that system. |
a) Give its sign magnitude representation. [2marks]
b) Give its one’s complement representation. [2marks]
c) Give its two’s complement representation. [2marks]
d) Why is the two’s complement preferable over the sign magnitude
and the one’s complement? [2marks]
2- i) Peter is a founder of the IT hardware solution company. He has recently employed John
and Gerard. For security purpose, he intends to build an automatic system to control
the main gate of the enterprise as followed:
– The gate opens when Peter is present at the gate alone
– The gate opens when Peter and one employee only are all present at the gate at the same time
– The gate remains locked otherwise
Draw the truth table for such a system using the following input and output variables
– S= the state of the gate
– P=Peter is present at the gate
– J= John is present at the gate
– G= Gerard is present at the gate [4marks]
ii) Given the following truth table below where A, B and C are input variables
and S the output signal
| A | B | C | S |
| 0 | 0 | 0 | 0 |
| 0 | 0 | 1 | 1 |
| 0 | 1 | 0 | 0 |
| 0 | 1 | 1 | 1 |
| 1 | 0 | 0 | 0 |
| 1 | 0 | 1 | 1 |
| 1 | 1 | 0 | 1 |
| 1 | 1 | 1 | 0 |
a) Write the Boolean expression of S as a sum of products. [2marks]
b) Draw the Karnaugh map table of output signal S. [2marks]
c) Use the karnaugh map to simplify the Boolean expression
| of the output S. iii) A 16 bit computer uses the floating point representation for real numbers as followed: |
[2marks] |
– One sign bit
– six bits exponent in excess notation
– Nine bit mantissa
a) Write the number -53.025 in the normalized binary floating
| point format. b) Determine the exponent in excess notation. |
[3marks] [2marks] |
c) Determine the mantissa. [2marks]
