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
- 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.
- [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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