Monday, August 2, 2010


PARITY BIT is a bit that is added to ensure that the number of bits is even or odd.
There are 2 types of parity bits:

1. Even parity bit

2. Odd parity bit


 In the even parity  if in a data for e.g.  no of bit 8 ,the no of  occurence of 1's is odd no of times, then we add 1 to it making entire set of bit even and making overall bit =9
e.g. 10001001 (1 occuring 3 times)
    110001001 (even parity)

and if the occurence of 1's is even no of times then we add a zero to make it even.
e.g  10001101 (1 occuring 4 times)
    010001101 (even parity)


In the odd parity , if data bit consists of odd no of 1's  we add a zero to it to make it odd.
e.g. 10001001(1 occuring 3 times)
    010001001 (odd parity)

similarly if data bit consists of even no of 1's we add a 1 to make it odd.
e.g. 10001101(1 occuring 4 times)
    110001101 (odd parity)

Even parity is a special case of a cyclic redundancy check (CRC), where the 1-bit CRC is generated by the polynomial x+1.

If the parity bit is present but not used, it may be referred to as mark parity (when the parity bit is always 1) or space parity (the bit is always 0).

(i hope you like the post. suggestions to improve and include more content clearly is welcomed)


  1. Thank you for writing the post.

    This comment is in general for all of you to consider while writing a post. Once you have finished writing, read through your post 1-2 times and make sure of the following:

    1. The language makes sense (for example, in this post - "if in a data for e.g. no of bit 8 ,the no of occurence of 1's is odd no of times", you probably wanted to say "a data with 8 number of bits and 1 occurring odd number of times" but your language was very confusing and hard to understand in the first read.

    2. Do not just introduce terms since it makes the post confusing (for example here you mentioned about CRC being generated by a polynomial). But this does not add any value and instead confuses the reader. You could have completely skipped the CRC part in this post if you think it would have been confusing. Similarly, the introduction of mark and space parity without the mention of where specifically it is used is confusing.

    3. I like that this post is short - someone else has also commented this thing on another post. Please make sure that whatever information you are passing is not too much overload and can not be specified in shorter text.

    Broadly, just dont rush to publish your post. A good post takes a lot of time and should go through a lot of self iterations.

    I hope this is some constructive feedback that others will also use while writing their posts.

  2. Nice work.

    Could you please explain a bit more about what exactly is 'Parity Bit' and why is it used?
    Secondly, you mentioned "In the even parity if in a data for e.g. no of bit 8 ,the no of occurrence of 1's is odd no of times, then we add 1 to it making entire set of bit even" . How is the entire bit set becoming even? Same for the other courses.
    Thirdly could you please elaborate a bit upon 'Cyclic Redundancy Check' , 'Mark Parity' and 'Space Parity'?

    I hope you don't mind my comments. :)

  3. @Amarjeet sir,your suggestions are very helpful,I hope all of us will keep that in mind.Thank u.
    @Akshay,Could u please also explain what is parity and why do we need it?..

  4. thank you amarjeet sir and others
    .i will surely take care of your suggestions and try to improve upon it..

  5. The examples were helpful. So thanks for that. :)
    But I have a few doubts.

    "the 1-bit CRC is generated by the polynomial x+1." - where does this polynomial come from?

    "If the parity bit is present but not used" - By the parity bit being used, do you mean that some error present during transmission was corrected with the help of the bit? And why is it called "mark parity" and "space parity" only when it's not used?