Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is Parity Checking Useful?

  1. Dec 18, 2012 #1
    I don't understand how parity error detection is any use since if there are an even number of mistakes, the errors won't be detected.

    If there's more to it than this please let me know.
     
  2. jcsd
  3. Dec 18, 2012 #2

    jedishrfu

    Staff: Mentor

    Yes its useful. Its used everywhere sometimes on individual characters being transmitted. It works best if you have a very clean comm channel and single bit fails occur rarely. Detection means the receiver can request a retransmission of the character. If the line degrades a lot then you'll get a lot of parity checks in a transmission then you can terminate the transmission (even though you may have missed the even bit errors) forcing the transmittor to send everything again.

    For more comprehensive error checking and repair, other schemes will be used with the attendant hardware/software complexity that goes with them.
     
  4. Dec 18, 2012 #3

    jim hardy

    User Avatar
    Science Advisor
    Gold Member
    2016 Award

    Wow.

    Back in the days of teletype machines and punched paper tape,

    parity check could tell you quickly if an individual character(byte) was corrrupted.

    That was handy because you could stop partway through a file load and reload the tape. Also it gave you a clue where in the tape to look for your trouble. Teletype machines read about ten bytes/second, and a high speed reader could do aout 400. Obviously we didn't do multi-megabyte files on paper tape.

    Usually a "Checksum" on the whole file was done at end of read, which will detect an even # of bit errors. That was deadly - you didn't know where to look.

    I liked paper tape - a corrupted file you could hold up to the light and see every bit. With Scotch tape and a pocket knife one could fix a corrupt file.

    But back then 32K was a lot of memory.

    old jim
     
  5. Dec 18, 2012 #4
    If you just talking about single parity check, you catch 50% only. But you don't just use one time, like Jim said, you have check sum and other check at the same time. So if the data pass all the check, it is quite reliable.......notice "quite"? Nothing is absolute.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Is Parity Checking Useful?
  1. Circuit checking? (Replies: 8)

  2. Parity and CRC (Replies: 1)

Loading...