IGCSE Computer Science Paper 1 Word Scramble: 2.2 Methods of Error Detection (Modules 155–164)
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Word scramble
Unscramble the letters and write each key term on the line.
1
NEVE APIRYT
A parity bit is added so the total number of 1s in the byte, including the parity bit, is even. Odd count of 1s in the data gives parity bit 1; even count (even 0) gives 0.
2
DOD ITRYAP
A rule where the parity bit is set so the total number of 1s in the byte, including the parity bit, is odd. Even number of 1s in the data gives bit 1; odd number gives bit 0.
3
UCNTO HTE S1
______ in the 7 data bits, then set the leftmost parity bit to 0 or 1 so the total number of 1s in the whole 8-bit byte matches the agreed rule (even or odd).
4
APTYIR HKCCE
The receiver counts the 1s in the whole received byte, parity bit included. If the count breaks the agreed even or odd rule, an error has occurred and is detected.
5
IYATPR YTBE
An extra byte sent after a block of data bytes. Each of its bits is the parity bit for one column (bit position) taken down across all the data bytes in the block.
6
APYRTI LOBKC ECCKH
Checks a block of bytes in two directions: a parity bit on every byte (row) and a parity byte for the columns, so the wrong row and column pinpoint the error.
7
TRIPAY LKOBC
Each byte gets a row parity bit, then a final parity byte holds the parity bit for each column. The corner bit is the parity bit of the parity bits, so it checks in both directions.
8
AFILDE OWR DAN LCUMON
In a parity block, the row and the column that both fail their parity check cross at the bit that changed. Flip that bit to correct a single-bit error.
9
NRRF-CUOORE RERRO
Four flipped bits at the corners of a rectangle keep every row and column parity correct, so a parity block check misses the error. Only one error can be located reliably.
Answer Key
IGCSE Computer Science Paper 1 · Modules 155–164
1NEVE APIRYT → even parity — A parity bit is added so the total number of 1s in the byte, including the parity bit, is even. Odd count of 1s in the data gives parity bit 1; even count (even 0) gives 0.
2DOD ITRYAP → odd parity — A rule where the parity bit is set so the total number of 1s in the byte, including the parity bit, is odd. Even number of 1s in the data gives bit 1; odd number gives bit 0.
3UCNTO HTE S1 → count the 1s — Count the 1s in the 7 data bits, then set the leftmost parity bit to 0 or 1 so the total number of 1s in the whole 8-bit byte matches the agreed rule (even or odd).
4APTYIR HKCCE → parity check — The receiver counts the 1s in the whole received byte, parity bit included. If the count breaks the agreed even or odd rule, an error has occurred and is detected.
5IYATPR YTBE → parity byte — An extra byte sent after a block of data bytes. Each of its bits is the parity bit for one column (bit position) taken down across all the data bytes in the block.
6APYRTI LOBKC ECCKH → parity block check — Checks a block of bytes in two directions: a parity bit on every byte (row) and a parity byte for the columns, so the wrong row and column pinpoint the error.
7TRIPAY LKOBC → parity block — Each byte gets a row parity bit, then a final parity byte holds the parity bit for each column. The corner bit is the parity bit of the parity bits, so it checks in both directions.
8AFILDE OWR DAN LCUMON → failed row and column — In a parity block, the row and the column that both fail their parity check cross at the bit that changed. Flip that bit to correct a single-bit error.
9NRRF-CUOORE RERRO → four-corner error — Four flipped bits at the corners of a rectangle keep every row and column parity correct, so a parity block check misses the error. Only one error can be located reliably.