Sorry so what exactly is wallet.dat? is that the wallet that each altcoin have developed for their own coin? and you keep in of desktop?
All bitcoin base altcoins have their own wallet.dat file which stores addresses together with the amount of coins you own, if you're using windows it can be found in the following directory to be exact.
C:\Users\*Your Computer Name*\AppData\Roaming\*Altcoin Name*