Checksum - what is it? how to compare? what software?

how do you read checksum? what am i comparing the values given by checksum to?

The checksum is for fw its makes sure your loading right fw on right drive if the checksum does not match the fw wont load. Many dvd drive comanys do this so you wont flash one model drive to another. a good example of this is 822 > 830, or 800 > 822 . the checksum wont let this happen even though the hardware is pretty much identical, in the case of 800 and 822, and 430 i think had little different PUH but the fw would still work, mostly on 822