External hard drive confusion

Hello! This may be a stupid question but i have to ask it...is it possible to save sessions to an external hard drive, open the file and make changes, save the changes all WITHOUT transferring the file to the system hard drive first? okay...if this is possible, then someone please help me select the proper hard drive! thank you for saving my sanity...

If I understand correctly, all you have to do is in the particular session aloocate all info to that external drive. All info from that point on should go there. I just bought an exteral firewire 120 gb 7200rpm. It works cool. durand

Thank you for responding. What drive did you buy? Are you able to open your sessions right from the new drive without copying them back to the system drive?