O-LevelComputer ScienceData Representation2210/12 · May/June 2025 · Q113 Marks
A computer stores data temporarily in random access memory (RAM).
- (a)RAM is one example of primary storage. Give one other example of primary storage.[1]
- (b)Give one reason why data is only stored temporarily in the RAM.[1]
- (c)The denary numbers 19 and 230 are converted to binary numbers to be stored in the RAM. Convert the two denary numbers to binary numbers. 19 230 Working space[2]
- (d)The hexadecimal numbers 35 and 8AD are converted to binary numbers to be stored in the RAM. Convert the two hexadecimal numbers to binary numbers. 35 8AD Working space[2]
- (e)The 8-bit binary numbers 01100101 and 01110000 are stored in RAM. The binary numbers are added together. Add the two binary numbers using binary addition. Give your answer in binary. You must show all your working. + 01100101 01110000[3]
- (f)An overflow occurs when two other 8-bit binary numbers are added together. Explain why the overflow error occurs.[2]
- (g)The negative denary number –22 is stored in RAM. Negative denary numbers can be represented as binary using two's complement. Give the two's complement 8-bit binary integer that would be stored for the denary number -22. You must show all your working. Working space Two's complement 8-bit binary integer[2]
Mark scheme
Marking points from the official mark scheme (May/June 2025). The mark or mark type is shown in brackets.
- [1] Any one from: • ROM • Cache
- [1] Any one from: • It is volatile storage // Data is lost when the power is turned off. • It needs to be regularly replaced by other data // The data regularly changes // Data needs to be constantly updated
- [2] • 10011 • 11100110
- [2] • 0011 0101 • 1000 1010 1101
- [3] One mark for each correct nibble (MAX 2) One mark for a correct method of working e.g. showing carries. + 11 01100101 01110000 11010101
- [2] Any two from: • The result is greater than 255 // The result is too large. • Cannot be stored in 8 bits // Cannot be stored in the number of bits available for the register
- [2] One mark for a correct working method e.g. flip and add One mark for correct answer 11101010
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