Epson Progression U12 - Manual (Page 108)

Note
If you are removing one hard disk drive and leaving one in
your computer, be sure to set the jumpers on the remaining
drive to indicate that you have only one hard disk drive.
Where to Go Next
If you are installing your first hard disk drive (i.e., there is no
other hard disk in your computer), you should install it in the
internal drive bay. Go to page 4-16.
If you are installing your second hard disk drive, you can
install it in the external or internal drive bay (although you may
want to reserve the slots in the external drive bay for diskette
drives or other accessible devices). To install a hard disk drive
in the internal bay, go to page 4-16. To install it in the external
bay, see the following section.
To remove a hard disk drive from the external bay, go to
page 4-14. To remove a drive from the internal bay, go to
page 4-25.
Installing and Removing Drives 4-5