5.5 Information coding systems Flashcards
How do computers represent characters?
Information coding systems
What does ASCII stand for?
American standard code for information interchange
How many bits does ASCII use and how many characters can it represent?
7 bits
128 different characters
Why was unicode introduced
Due to the internet being more widely used there was a requirement for a coding system that could represent characters other than the latin alphabet.
Why is unicode better than ASCII
It can represent much more characters
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.
Describe how a parity bit works and what it is used for?
A single bit is added to transmission
Used to check for errors in transmitted data
Two types of parity: odd and even
Number of ones adds to make odd/even number
When data received a parity check is carried out.
If the parity is incorrect data is requested to be retransmitted
What is the main issue of parity bits?
If an even number of bits are changed during transmission error is not detected
Describe how majority voting works?
Each bit of the data is transmitted multiple times.
When received, the most commonly occurring value is taken to be correct
There’s no need for retransmission like when using a parity bit
Majority voting can correct errors when multiple bits change
What is the main disadvantage of majority voting?
the volume of data being transmitted is increased with the repetition of bits. increasing transmission time
Describe how checksums work?
A value is appended to the transmitted data
This value is determined by the data itself
Once received, the recipient removes the checksum
A check is carried out to ensure that the checksum matches the transmitted data
If the two do not match, the recipient cannot correct the error itself
In this situation, the recipient asks the sender to retransmit the data
Describe what a check digits is?
A check digit is a type of checksum
A single digit is added to the transmitted data
The single digit is calculated from the other digits
