How can I combine multiple hard drives in an operating system?

13 Dec 2011
13 Dec 2011 | |

How do I setup a computer I am building that will use two 40GB hard drives as if the two drives were one 80GB drive? Does the system ask which drive I wish to use for both the OS and susequent downloads? Every time? Can I make a choice so that drive “C” is primary and drive “X” is the secondary?