To be pedantic you actually have space and hardware to mount two extra drives. One mounts over the existing drive, and assuming you don't want a second optical drive the other mounts under the CD/DVD. The wiring harnesses are already there waiting. It's the work of a few minutes (and there are Internet sites to show you exactly how). The only advantage of the external Firewire hard drive is that you can share it with other (non networked) computers. Mounting the drive internally will be faster. I would suggest you keep the existing 'system' drive as is and use your new drive for all media and virtual ram disk space. FWIW Perry ________________________________________ From: Michelle A) install it INTO my Sawtooth in the "second" drive available spot? (I didn't know there was such a spot/slot...) B) replace the current (27GB?) hard drive with this new, bigger drive of 120 GB C) put this new drive into a firewire enclosure (for about $50 more?), and use it as an "external" storage/drive IF I chose to do Option C, why would that (or would that) be faster than just buying an external firewire hard drive in the first place? I am not a technician in ANY way, but I did manage to follow the specific directions thus far to upgrade this computer. I primarily need the upgrades now to handle my work with Photoshop. Buying a new Mac is just not in the budget at this time.