DDR3 RAM 6GB

Depends on the Module of DDR3 RAM that you choose If you have

1 Stick of 1GB you'll need 6 Sticks of the same to get 6GBof RAM on the Mobo, but that means you need 6 slots on the Mobo.

1 Stick of 2GB you'll need 3 Sticks for the same but that's not advisable if you have a 4 slot Mobo

1 Stick of 4GB well .... you'll need 1 and a Half stick..... lol again not advisable......

It's safer to go with 4Sticks each of 2GB and get that extra 2GB...... The more the better I guess if you need 6GB the leap to 8GB isn't very far ahead when it comes to RAM.....