IGCSE Computer Science Paper 1 Word Scramble: 2.2 Methods of Error Detection (Modules 179–188)
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Word scramble
Unscramble the letters and write each key term on the line.
1
KECCH ITGID
The last digit of a bar code number, worked out from the other digits. The scanner recalculates it and rejects a misread if the digits do not match, so the item must be scanned again.
2
HECKC TDIIG TIITALNIOM
A wrong number can still pass the check digit test, and a valid number may belong to the wrong item. The check digit tests the digits only, not what they mean.
3
RAQ
Automatic repeat query: the receiver checks data for errors and replies. If the data is bad or no reply arrives, the sender automatically resends it until it is received correctly.
4
IMTUOET
The set time a sender waits for an acknowledgement after sending data. If none arrives in time, it assumes the data was lost and resends it.
5
QRA TILSIM
ARQ resends data when a separate check finds an error, so it misses errors that check misses, and a noisy link causes many resends that slow the transfer.
6
RRORE NETECDOTI TEHDMO
Parity, parity block, checksum and echo check find errors in transmission; a check digit finds them at data entry; ARQ asks for a resend. Each sends different extra data.
Answer Key
IGCSE Computer Science Paper 1 · Modules 179–188
1KECCH ITGID → check digit — The last digit of a bar code number, worked out from the other digits. The scanner recalculates it and rejects a misread if the digits do not match, so the item must be scanned again.
2HECKC TDIIG TIITALNIOM → check digit limitation — A wrong number can still pass the check digit test, and a valid number may belong to the wrong item. The check digit tests the digits only, not what they mean.
3RAQ → ARQ — Automatic repeat query: the receiver checks data for errors and replies. If the data is bad or no reply arrives, the sender automatically resends it until it is received correctly.
4IMTUOET → timeout — The set time a sender waits for an acknowledgement after sending data. If none arrives in time, it assumes the data was lost and resends it.
5QRA TILSIM → ARQ limits — ARQ resends data when a separate check finds an error, so it misses errors that check misses, and a noisy link causes many resends that slow the transfer.
6RRORE NETECDOTI TEHDMO → error detection method — Parity, parity block, checksum and echo check find errors in transmission; a check digit finds them at data entry; ARQ asks for a resend. Each sends different extra data.