Can anyone help me understand how Parity Bit Check works? (1 Viewer)

[S4Saustralia]

Tell me if I am correct:

Parity bit check is the 8th bit within a byte. All other bytes are represented with an ascii character, but the 8th bit is used to check whether a byte has been successfully received by counting the number of 1's within the byte.

Eg: id the 8th bit knows there should be an odd number of 1's and has the 7 bits as 0101010 it will add another 0 and become 01010100?

However, what I dont understand is wont the 8th bit always add a 0 if correct? Eg: if he knows that there should be an even or odd amount of 1's, he will always add a 0 if he sees the correct amount..

Also, if the 8th bit does get the wrong number of 1's and has to add a 1, wont that corrupt the file by altering the data?

Sorry for all the questions, but my teacher really skimmed through it and the concept is fucking with me.

Thanks

 

[harrisony]

Tell me if I am correct:

Parity bit check is the 8th bit within a byte. All other bytes are represented with an ascii character, but the 8th bit is used to check whether a byte has been successfully received by counting the number of 1's within the byte.

Eg: id the 8th bit knows there should be an odd number of 1's and has the 7 bits as 0101010 it will add another 0 and become 01010100?

However, what I dont understand is wont the 8th bit always add a 0 if correct? Eg: if he knows that there should be an even or odd amount of 1's, he will always add a 0 if he sees the correct amount..

Also, if the 8th bit does get the wrong number of 1's and has to add a 1, wont that corrupt the file by altering the data?

Sorry for all the questions, but my teacher really skimmed through it and the concept is fucking with me.

Thanks

ASCII is a 7 bit code although when packed into a byte then the 8th bit is used as a parity bit. Although not all bytes include a parity (Unicode doesn't)

It depends if you're using an even or odd parity, if you're using an odd parity in your example then yes

I don't get what you mean
edit: ok, going to try and answer - both systems must use the same parity (even or odd), if they don't then you would have a big problem

As in if the computer counts 3 1's when it should have counted 2 1's?

 

[ohexploitable]

your

Ugh. You did it twice :-(

 

[harrisony]

Ugh. You did it twice :-(

oh shut up

 

[terminator69]

Parity bit check is the 8th bit within a byte. All other bytes are represented with an ascii character

That doesn't make any sense.

However, what I dont understand is wont the 8th bit always add a 0 if correct? Eg: if he knows that there should be an even or odd amount of 1's, he will always add a 0 if he sees the correct amount..

Why would it always add 0 if it can have an even number of 1s? And stop referring to code as "he".

Also, if the 8th bit does get the wrong number of 1's and has to add a 1, wont that corrupt the file by altering the data?

You're saying that the computer might not know how to add? That's not possible.

Ignoring the idea that computers forget how to make simple calculations, parity bit error detection is not very accurate anyway. If a bit is changed throughout transmission, it will corrupt the file and the byte will need to be resent. Although, it only has a 50% success rate so if two bits are corrupted in transmission (ie. 0 to 1 and 1 to 0), then the receiver will accept it as a successful transmission because all the 1s add up to the same odd or even parity, even though the byte is corrupted.