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O-LevelComputer ScienceData Transmission2210/12 · Oct/Nov 2022 · Q54 Marks

8 bytes of data are transmitted from one computer to another. Each byte of data has a parity bit. The data is also sent with a parity byte. Each bit in the parity byte allows a check to be performed on each column of bits. A parity check is performed on the data and an error is found in one bit. The table shows the data that was received. Parity bit | Bit 2 | Bit 3 | Bit 4 | Bit 5 | Bit 6 | Bit 7 | Bit 8 ---|---|---|---|---|---|---|--- Byte 1 | 0 | 1 | 0 | 1 | 0 | 0 | 1 | 1 Byte 2 | 1 | 0 | 0 | 1 | 1 | 1 | 1 | 1 Byte 3 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 0 Byte 4 | 1 | 1 | 0 | 1 | 0 | 1 | 0 | 1 Byte 5 | 1 | 0 | 0 | 0 | 1 | 1 | 1 | 0 Byte 6 | 1 | 1 | 1 | 0 | 1 | 0 | 1 | 1 Byte 7 | 1 | 1 | 0 | 0 | 1 | 1 | 0 | 0 Byte 8 | 1 | 1 | 1 | 1 | 0 | 0 | 1 | 1 Parity byte | 1 | 0 | 1 | 1 | 0 | 1 | 1 | 1 Identify which bit has an error by giving the Byte number and Bit number. Explain how you found the error. Byte number Bit number Explanation

  1. Identify which bit has an error by giving the Byte number and Bit number. Explain how you found the error. Byte number Bit number Explanation[4]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.

  1. [4] 5 One mark each for the correct byte and bit • Byte 4 • Bit 5 Any two from: • Counted all the 1s • An even parity has been used • Odd number of ones in that row (byte 4) and column (bit 5)

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About this question

Topic
Data Transmission, O-Level Computer Science (syllabus 2210). Structured question, 4 marks.
Source
O-Level Computer Science, Oct/Nov 2022 Paper 1 Variant 2, question 5.

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