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

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2024). The mark or mark type is shown in brackets.

1. [4] 5(a) 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
2. [3] 5(b)(i) • Bits are sent one at a time • Bits are sent down a single wire • Data is sent in one direction only
3. [3] 5(b)(ii) 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
4. [2] 5(b)(iii) 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