I wanted to take the backup from my old hard disk

Hi Friends,
I got a new dell XPS 420 Desktop in that I have 1 hard desk I can connect 2 drives in that desktop. Now I wanted to take the backup from my old hard disk. Can I connect it to the additional slit available if yes, what drive it shows?
At present I have 2 partitions C & D. I don’t want to lose the data can anyone help with this.
Thanks in advance.
