tim@minn-ua.UUCP (Tim Giebelhaus) (02/29/84)
I am posting a question for a friend. There is supposed to be a Cyclical Redundancy Check formula. I don't know if it supposed to check statisticaly from a series of points or if it is to check the higher orders of the function. Anyway, if you have any information about this formula or something resembling it, could you please send me some mail about it.
jones@fortune.UUCP (03/15/84)
#R:minn-ua:-101900:fortune:8600014:000:1036
fortune!jones Mar 14 18:57:00 1984
Cyclical Redundancy Check (CRC - also referred to as Cyclical
Redundancy Code) is a enhanced method of parity checking data.
It is typically found in tape and disk magnetic storage devices.
Essentially, the data stream is divided by a selected polynomial
and the remainder is appended to the data block. When reading
the data the data stream is divided (the divide is performed by
an exclusive-or and shift) by the same polynomial. In a binary
system, feeding in the remainder, in addition to the data, zeroes
the result. Therefore, if the result is nonzero, then the data
is in error. Clearly, a multibit failure which matches the
generator polynomial would not be caught. However a cleverly
selected polynomial will catch burst errors of up to 3/4 the
length of the generator polynomial. Floppy disks use a 16 bit
CRC for data fields of up to 1 Kbytes.
Dan Jones
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