Are Mountain Dew and Vault the same thing?

They taste the same, I get them out machines right next to each other. They both cost the same. If one is out, I get the other without any hurt feelings. Mountain dew is a pepsi product, Vault is Coke. I have never heard a Vault commercial say the Words, "Do the Dew." a better question might be, "do they really have to abbreviate the Word mountain on the MTN DEW bottle?"