O-LevelComputer ScienceData Transmission2210/12 · May/June 2018 · Q54 Marks

The three binary numbers in the registers X, Y and Z have been transmitted from one computer to another. Parity bit Register X 1 0 0 1 0 0 1 0 Register Y 1 1 1 0 0 1 1 1 Register Z 1 1 1 0 1 0 0 1 Only one binary number has been transmitted correctly. This is identified through the use of a parity bit. Identify which register contains the binary number that has been transmitted correctly. Explain the reason for your choice. The binary number that has been transmitted correctly is in Register Explanation

The three binary numbers in the registers X, Y and Z have been transmitted from one computer to another. Parity bit Register X 1 0 0 1 0 0 1 0 Register Y 1 1 1 0 0 1 1 1 Register Z 1 1 1 0 1 0 0 1 Only one binary number has been transmitted correctly. This is identified through the use of a parity bit. Identify which register contains the binary number that has been transmitted correctly. Explain the reason for your choice. The binary number that has been transmitted correctly is in Register Explanation[4]

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Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

[1] Register Y
[1] Count the number of 1/0 bits (in each byte/register)
[1] Two bytes/registers have an odd number of 1/0 bits // Two have odd parity
[1] Even parity must be the parity used
[1] One byte/register has an even number of 1/0 bits // One uses even parity
[1] The two with an odd number of one bits/odd parity are incorrect // Register X and Z should have even parity

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