Check Digits (Cambridge (CIE) O Level Computer Science)
Revision Note
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Check Digits
What is a check digit?
A check digit is used to determine if data has been corrupted but does not reveal where
Data is sent in blocks and an additional check digit value is added at the end of the block
Check Digits are custom, user-created algorithms that perform mathematical calculations on data
Examples of where check digits can be used include:
ISBN book numbers
Barcodes
ISBN book numbers
Each book has a unique ISBN number that identifies the book
A standard ISBN number may be ten digits, for example, 965-448-765-9
The check digit value is the final digit (9 in this example).
This number is chosen specifically so that when the algorithm is completed the result is a whole number (an integer) with no remainder parts
A check digit algorithm is performed on the ISBN number and if the result is a whole number then the ISBN is valid
Barcodes
Barcodes consist of black and white lines which can be scanned using barcode scanners
Barcode scanners shine a laser on the black and white lines which reflect light into the scanner
The scanner reads the distance between these lines as numbers and can identify the item
Barcodes also use a set of digits to uniquely identify each item
The final digit on a barcode is usually the check digit, this can be used to validate and authenticate an item
Worked Example
Check digit algorithms are used to determine whether an error has occurred in transmitted data.
State the names of two examples of a check digit algorithm.
[2]
Answer
ISBN [1]
Barcode [1]
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