5.5 Information coding systems Flashcards
How do computers represent characters?
Information coding systems are used to match characters to character codes.
Why was Unicode introduced?
As the internet became widely used throughout the world, there was a requirement for an information coding system that could represent new characters. Unicode was introduced in 1991 to allow the representation of a wider variety of alphabets by computers. The standard uses 8 to 48 bits per character.
What is the purpose of error check methods in data transfer?
When data is transferred between computers there is a chance of errors that can cause the data to change during transmission which can have bad consequences. To reduce the chances of incorrect data being used, there has been a development of error checking methods.
Describe how a parity bit works?
A parity bit is added to a transmision and it can be used to check for errors in transmitted data. Its value is calculated based on the transmitted data itself. The parity bit can have 2 forms - Even parity and odd parity. The value of the parity bit is chosen as to make the total number of 1s even or odd depending if the parity bit is decided to be odd or even.
What is the main issue of parity bits?
Whether using odd or even parity if an even number of bits is changed during transmission the error is not detected.
Describe how majority voting works?
When using majority voting each bit of the data is transmitted multiple times. When the data is received the most commonly occurring value is taken to be correct.
What is the main disadvantage of majority voting?
The primary disadvantage is the that the volume of data being transmitted is increased with the repletion of bits.
Describe how checksums work?
Checksums involve adding the value, determined by the data itself to the transmitted data. An algorithm is used to determine the value of a checksum based on the data being transmitted. The modulo function is commonly used. Once received the recipient can remove the checksum and apply the same algorithm as was used when sending the data to ensure that the checksum matches the transmitted data. If the two do not match the recipient cannot correct the error itself so must request that the sender retransmits the data.
Describe how check digits work?
A check digit is a type of checksum in which only a single digit is added to the transmitted data. This reduces the number of different algorithms that could be used to calculate the value of the check digit and so it reduces the variety of errors that the method can detect.
