Can someone enlighten me on the wonders of "checksum"?

Someone told me that when Windows saves and closes a file
a checksum is calculated for that file. Then when the
file is reopened the checksum is recalculated and compared
to the original.

Does this really happen? If so, what would happen if the
checksums were different? What could cause this to
happen? TIA

"Hawk" <(E-Mail Removed)> wrote in message
news:56de01c3e522$474f8b70$(E-Mail Removed)...
> Can someone enlighten me on the wonders of "checksum"?
>
> Someone told me that when Windows saves and closes a file
> a checksum is calculated for that file. Then when the
> file is reopened the checksum is recalculated and compared
> to the original.
>
> Does this really happen? If so, what would happen if the
> checksums were different? What could cause this to
> happen? TIA

the only file checksum used by ms that i know of was an old msdos way of
checking the dos kernal executable. there were (and maybe still are) anti
virus programs that create checksums of files to detect changes... they left
little hidden files in all the directories of the system that had the
checksum signatures of the files in it. there is new stuff in the .net
framework that can compare hashes of files and encrypted signatures against
the file hash to validate executables.