To quote from the PCSTATS website "One thing that is immediately noticed upon opening up the Dimension 2400 is that it lacks much future expansion room. Specifically, there is no place to add an extra hard disk, unless you were to jury-rig one onto the spare 5.25" drive bay" . I would therefore suggest that you opt for an external hard drive connected with a usb port. While they may not be as fast as internal drives they can be far more useful in that you can transfer the drive to just about any computer very easily. You can get these drives from many places and prices and sizes vary, choose the largest you can afford. You can also buy external hard drive enclosures that you add your own drive to, this can work out cheaper if you happen to have an old internal drive going spare.