A simple error-detection scheme in which each transmitted message is accompanied by a numerical value based on the number of set bits in the message. The receiving station then applies the same formula to the message and checks to make sure the accompanying numerical value is the same. If not, the receiver can assume that the message has been garbled.
There are different hashes such as CRC/CRC32 (Cyclic redundancy check) and MD5. Using a program such as F-CRC Calculator can generate the CRC32/MD5 of a file. If two files are the same they will have the same hash(es). If one part of the file is changed (except the file name*) then the hash changes.
Use for Hash
One can use Beyond Compare to determine if two files are the same, it has a CRC compare mode (oposed to binary (Where it checks the file itself)), however, it does not give the CRC, it just calculates the CRC of both files and informs the user if it matches. Hash compare can beat Beyond Compare over a network as it's easier to generate the hash on the remote computer (Remote control, ex. VNC) and do the same locally and look if they numbers match than to have Beyond Compare read the file locally and then load the file over the network, by running apps like F-CRC Calculator over the network all the computing is done remotely this saving bandwidth.
Torrents store hash to help distribute the files.
External Link/See also
F-CRC Calculator
Hash Tab
Torrent
MD5 Page (So in Mac there is a command md5 to find the hash, shit I was looking for an app to calculate hash forever….
