This CRC.COM program for MSDOS determines the two byte CRC or Cyclic Redundancy Check of a file or program. It is a benchmark for the integrity of the file or program's contents down to the last bit. Whereas a checksum, the old standby in error detection from the early days of computing, could be confounded by two or any even number of bits being wrong in equal valued places, sometimes typical with memory defects, the cyclic redundancy check is a polynomial series result that is billions of times less likely to be incorrect about a file's integrity. It is used thus: CRC FILENAME.EXT and this results in a two byte hexadecimal number. That the number is hexadecimal and you don't know hexadecimal is unimportant, as long as the two bytes are the same as the last time you ran this program on the file or program in question. It also serves as a benchmark for virtually any type of viral infestation, although it doesn't report this to you, merely the fact that an incorrect copy of the program is present, if the bytes fail to match previous values or a value given for that file in its documentation for a two byte CRC. There are three and more byte CRC's, but this is for user edification and is by no means shabby for the size of the files it can handle safely. Note that only one in 65536 files might have a CRC of the same value, and it wouldn't likely resemble your program under scrutiny!
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