checksum is used to make sure that all the data that was sent has arrived. it can be calculated by adding all the bits up in the data or all of the data blocks. this is then send afterwards and used to check if everything is there.
parity system uses an extra bit called a “parity bit” this insures that the number of 1s is always odd or even. this was decided by both sides before the data was sent
majoroty voing is when your bits are sent 3 times and the most common bit is used. 101100 is sent as 111000111111000000. it is recived as 110 000 110 111 001 000 which = 101100
they all do a simalar job. majoroty voting is very good but the data is sent 3 or more times. this is ineficsnt and slow. parity system doesnt check if everything is right but only that there are the correct number of 1s. checksum is good for very large pieces of data. this only valadates that the right value of data arrived and not if it is order.
ascii is used to represent characters using 7 bit binery. it can represent upto 128 characters. extended ascii ads an extra bit onto this allowing upto 256 characters. these are older and not used so much. they work on most devices but just dont have enough characters to make them usefull for anything other than plain text
unicode on the other hand is more used as it can represent more than 1.1 million characters. it uses ascii for the first few values doing british characters but also does over 30 other character sets. often using UTF-8 To ENCODE. it uses Hex numbers so uses the base 16 number set. the letter a lookes like this ~U+1F60A~
unicode is used almost everywhere. there is very few use cases to only use ascii other than if storage is limmated to below 64mb or less than 8mb ram. as ascii has such a low ammount of characters. unicode also does emojies so is all around better