A-LevelComputer ScienceData representation9618/12 · Oct/Nov 2021 · Q48 Marks

A register stores the following binary number: 1 1 0 0 1 1 0 1

(a)The binary value in the register represents an unsigned binary integer. Convert the unsigned binary integer into denary.[1]
(b)The binary value in the register represents a two's complement binary integer. Convert the two's complement binary integer into denary.[1]
(c)The binary value in the register represents a hexadecimal number. Convert the binary number into hexadecimal.[1]
(d)State why the value in the register cannot be interpreted as a Binary Coded Decimal (BCD).[1]
(e)(i)The binary contents of two registers are: Register 1 0 0 1 1 1 1 0 1 Register 2 0 0 1 0 1 1 0 1 Add the contents of Register 1 and Register 2. Show your working.[2]
(e)(ii)Subtract the contents of Register 2 from the contents of Register 1. Show your working.[2]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2021). The mark or mark type is shown in brackets.

[1] 205
[1] -51
[1] CD
[1] The denary value in each group of 4 bits is greater than 9 // the denary value in each nibble is greater than 9
[1] 1 mark for working, 1 mark for answer
[1] Correct working (showing carries)
[1] Correct answer: 0110 1010
[1] 1 mark for working, 1 mark for answer
[1] Correct working (converting Register 2 to two's complement and adding)
[1] Correct answer: 0001 0000

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