adding a second hard drive

Here's your Service Manual with directions for adding a drive. No caddy needed. It should fit into an empty bay that's the right size. If you bought a hard drive kit, everything you need is included. You need to format the drive according to the directions that came with the drive or check the drive manufacturer's web site.

Check the bay below the existing drive - you do need a mounting frame for a second drive, which may not be included with the system (if it's there you'll see it in the empty bay).  The drive must be mounted in this flexible plastic frame, as it slides into the case without the use of screws.  As I recall, the 3100 did not come with an empty frame, in which case you will need two things to mount the drive:  A SATA cable with at least one right-angle connector (you have very little clearance between the drive and the door to the case) and the plastic drive carrier.

This is the drive carrier:

http://www.txcesssurplus.com/servlet/the-6126/Dell-Dimension-Optiplex-Precision/Detail

Hi, thanks for your kind help,   regards macarra61

Hi, thank you for your kind help, i will get the two items that you said i will need. Regards macarra61