Two Sata HDD's, how do I tell which one it will boot from?

My buddy has been using a 1TB HDD and it is almost full so he bought a second hard, a Sata 2tb hard drive. Right now he has the 1TB drive taken out of the pc, hooked up the 2TB hdd and is installing Windows on it right now.

Once he is done and the pc is booting Windows from the 2TB drive, he wants to hook the 1TB drive back up and it be the D: drive. How would we do this? What determines with Sata hard drives which one the pc will end up making the primary drive?

In the old days with IDE drives we could just set one to Master and one to slave. With Sata drives would we do the same thing, or what do we do so that the pc knows he wants to use the TB drive as the primary bootable Windows drive. Remember, the 1TB drive has Windows on it already, he wants to be able to boot up, copy off the stuff he wants off of it over to the 2TB drive, then format the 1TB drive.

All you should have to do is go into the bios and set the the 2TB drive as the boot drive/primary and the 1TB drive as secondary. From then on it should boot windows from the 2TB drive and you will be able to copy your files and format the 1TB drive.

Based on the serial # in the bios HDD priority menu.

When he went into the Boot Device Priority list it only listed the new 2TB drive which is what he wanted to boot off of anyways. Once he booted up into windows it then showed the other 1TB drive as the F: drive so everything worked out great.

Thanks for the info\responses. Much appreciated.