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Computer Science · May / June 2021 · Paper 11 · Question 8

0478

As printed in the paper

The question as text

Four 7-bit binary values are transmitted from one computer to another. A parity bit is added to each binary value creating 8-bit binary values. All the binary values are transmitted and received correctly.

Read automatically from the paper; the printed page above is exact.

Show the answer and mark scheme

  • 8(a)[4]

    Odd
    Odd
    Even
    Even

  • 8(b)[1]

    Any one from:

    there is a transposition of bits
    it does not check the order of the bits (just the sum of 1s/0s)
    even number of bits change
    incorrect bits still add up to correct parity

  • 8(c)(i)[4]

    Four from:

    Multiple bits are sent at the same time
    Uses multiple wires
    Data is sent in both directions …
    … but only one direction at a time

  • 8(c)(ii)[2]

    Any two from:

    Bits may arrive skewed
    More expensive to setup/manufacture/purchase cable
    Limited distance
    More prone to interference/error
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