Computer Science · Oct / Nov 2024 · Paper 12 · Question 5

0478

As printed in the paper

The question as text

A barcode scanning system uses a check digit to check for errors in data on input.

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

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5(a)[4]
Any four from:
A check digit is calculated from/using the barcode data
… using an algorithm // by example e.g. Modulo 11
… and added to the barcode
When/after the barcode is scanned the check digit is recalculated …
… using the same algorithm
If the check digits do not match an error has occurred when scanning the barcode // If the check digits match no error has occurred when scanning the barcode
5(b)(i)[3]
Bits are sent one at a time
Bits are sent down a single wire
Data is sent in one direction only
5(b)(ii)[3]
Any three from:
The stock control system may be a long distance away
… parallel should not be used in long distance transmission // Serial is more reliable for long distance transmission
The data does not need to be sent quickly
… the increased speed of parallel is not needed
… as only small amounts of data need to be sent
The bits are sent/arrived in order
… the data will not be skewed // the data could be skewed if parallel was used
… there will be no data collisions
There will be less interference/crosstalk (due to single wire)
… there will be fewer errors in the data
No need for a reply/response from stock control system
… half-duplex/full-duplex is not necessary as only one way transmission needed
5(b)(iii)[2]
Any two from:
(Odd/even) Parity check // Parity byte check // parity block check
Checksum
Echo check
(Positive/negative) ARQ // Automatic repeat query // Automatic repeat request

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