Can I install one game from a DVD in multiple computers?

[Jeremy]

Suppose I buy an original PC game DVD like Assassin's Creed 3 from the store and install it on my home computer and play it online. After that, I can take that DVD to my friend's house and install it on his computer and play online from there? I think it's not possible to play it from both computers at the same time but can I play it from one computer one at a time? Also, another question. After I install the game using the DVD, do I need to have the DVD inserted in order to play the game or can I take out the DVD after installation?
Can you elaborate on what you mean by the memory being different?
As I've mentioned, I'm talking about original copy of a game, not pirated ones. I need the original in order to play online/multiplayer.
I can't find any keygens anywhere that doesn't have surveys.

 

[MonkeydeLuffy]

Most games, especially newer ones require CD-keys (which prevent you playing online from multiple systems using the same key). Also I'd say more games than not do require the disc to play. To get around these things, at least one person will need to find a CD-key-generator specific to your game so you can use different keys to play at the same time. Then whoever doesn't have the disc would need a CD-crack (specific to the game) that would allow you to play without a disc.

Now, if it were a game like Starcraft II, you'd probably have a lot of difficulty playing that on multiple sytems, as the games are account-bound, and you can only get an account through purchasing the game. But something like Assassin's Creed 3 you should be able to find a key-gen and a crack online fairly easily. Though, I know with the Xbox 360 version you need a U-play account, but if you both have one it should be fine (if you both had Brotherhood you would have received one).