IGCSE COMPUTER SCIENCE UNIT 2
(DATA AND ENCRYPTION) TEST
QUESTIONS WITH COMPLETE
SOLUTIONS
Causes and Effects of Transmission Errors: - Answer-Electrical interference
Power surges
Synchronisation issues
Wear and tear on the cable or connectors
Data can be lost
Data can be gained
Data can be changed
What is parity check - Answer-- One bit is used as a parity bit; used to check for an error
- Even Parity: If the Number of 1s is odd, then the parity bit is set to 1. If there is an
even number of 1s, the parity bit will be 0
- If there is an error, the receiving device notifies the transmitting device, and the data is
resent
What is a parity block check - Answer-- In a parity block check, each byte has a parity
bit,
whilst an additional parity byte is sent at the end of
the block
- First identify the faulty byte, and then the faulty bit by consulting the Parity byte. Then,
through the row and column, find the offending bit and correct it.
What is checksum - Answer-- It is important to check that a file received has no errors
introduced
- The file is run through an algorithm on the transmitting side that produces a checksum
which is sent to the receiving computer
- The receiving computer also calculates the checksum, and compares with the sent
checksum
What is echo check - Answer-1. Data transmitted to the receiver
2. Same data is transmitted (echoed) back to the transmitter
3. Transmitter compares the data with the original. It it doesn't match, the data is
transmitted again.
Describe how a check digit works, include examples - Answer-- ISBN or barcodes
- A check digit is added to the end of a set of numbers to check for mistakes
(DATA AND ENCRYPTION) TEST
QUESTIONS WITH COMPLETE
SOLUTIONS
Causes and Effects of Transmission Errors: - Answer-Electrical interference
Power surges
Synchronisation issues
Wear and tear on the cable or connectors
Data can be lost
Data can be gained
Data can be changed
What is parity check - Answer-- One bit is used as a parity bit; used to check for an error
- Even Parity: If the Number of 1s is odd, then the parity bit is set to 1. If there is an
even number of 1s, the parity bit will be 0
- If there is an error, the receiving device notifies the transmitting device, and the data is
resent
What is a parity block check - Answer-- In a parity block check, each byte has a parity
bit,
whilst an additional parity byte is sent at the end of
the block
- First identify the faulty byte, and then the faulty bit by consulting the Parity byte. Then,
through the row and column, find the offending bit and correct it.
What is checksum - Answer-- It is important to check that a file received has no errors
introduced
- The file is run through an algorithm on the transmitting side that produces a checksum
which is sent to the receiving computer
- The receiving computer also calculates the checksum, and compares with the sent
checksum
What is echo check - Answer-1. Data transmitted to the receiver
2. Same data is transmitted (echoed) back to the transmitter
3. Transmitter compares the data with the original. It it doesn't match, the data is
transmitted again.
Describe how a check digit works, include examples - Answer-- ISBN or barcodes
- A check digit is added to the end of a set of numbers to check for mistakes
