Advanced level 2025 Centre regional mock guide Computer Science 2
Advanced level 2025 Centre regional mock guide Computer Science 2
The system stores floating point numbers in normalized form using 2’s complement, with an
8-bit mantissa and a 4-bit exponent as follows.
Mantissa Exponent
(i) State the value of 1011 1110 0100 in denary if it represents a two’s complement floating point number. (2 marks)
(ii)This floating-point number is said to be normalised. How does the bit pattern indicate that this number is normalised?
(2 marks)
| (b) (i) How many 32K x 1 RAM chips are needed to provide a memory capacity of 256 K bytes? (ii) A computer memory is composed of 16 chips, each of size 4K x 8. |
(2 marks) |
How many memory locations are there in this memory? (2 marks)
How many address bits are needed to address this memory? (2 marks)
(c) IBM wants to build a computer chip that compares English Language words to see if they are the same. To begin with, they
would like to build a smaller one that bit-wise compares two characters. Each character is coded in 8 bits. The principle they
follow here is that in bit wise comparisons, a 1 (one) is generated if the two corresponding bits are the same otherwise a 0
(zero) is generated.
| (i) Give the truth table for the comparison of two bits. (ii) From the table generate a Boolean expression for the comparison of two bits x and y giving as result. |
(2 marks) (2 marks) |
| (iii) (iv) |
Draw a digital circuit diagram for this comparison with r as the output. What logic gate is been described here? |
(2 marks) (1 mark) |
2 (i) A computer design company has been asked to produce a design for an elementary computer to be used to teach
students about machine architecture, machine operations and the design of an instruction set. The current instruction register
has a length of 16 bits. The accumulator has a length of 16 bits. The size of each memory location is 16 bits. The current
instruction register is designed to hold one machine instruction at a time. A machine instruction is 16 bits in length. The most
significant eight bits of a machine instruction denote the machine operation. The least significant eight bits denote an operand
or an address of an operand. Main memory stores both instructions and data. The structure of a machine instruction is as
follows:
