IGCSE Computer Science Paper 1 Definitions Worksheet: 2.2 Methods of Error Detection (Modules 155–164)
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Key terms
Write what each term means, in your own words.
1
even parity
2
odd parity
3
count the 1s
4
parity check
5
even number of bits change
6
parity byte
7
parity block check
8
parity block
9
failed row and column
10
four-corner error
Answer Key
IGCSE Computer Science Paper 1 · Modules 155–164 · Student wording will vary for definitions
1even 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.
2odd 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.
3count 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).
4parity 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.
5even number of bits change — A single parity check misses an error when an even number of bits change, because the count of 1s keeps the same parity. It also cannot show which bit is wrong.
6parity 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.
7parity 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.
8parity 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.
9failed 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.
10four-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.