Checking hashsum

Why do you to check hashsum?

It's a short representation of file content. The main thing about that - it's short and can be easily compared. If 2 files have the same hash, it means they are the same. If they have different hash - they are different.

It becomes useful when you downloaded file and want to make sure it's the right thing. For example SHA-1 of orginal 0.99 UFO:TTS binary is ea288af818533c2ff193fdb2a0df5d84c63b34c7. It means if you have the same - you can be sure that it hasn't been modified.

How to calculate it?

On Linux it's better to use sha1sum tool.

On Windows you have you can select some user friendly tool that shows hashes in file properties (like this). If you don't want to install anything, you can go with hardcore option - tool that should be run from command prompt (like this).