A RAM drive is a partition set up in RAM, which acts like a regular drive. If you have a gig of RAM, and you set up a 600MB RAM drive, then you essentially have 400MB of RAM available to the system. The upside to a RAM drive is obviously speed - file transfers go at the speed of your memory bus - in most modern cases, that would be measured in gigabytes per second. The downside to a RAM drive is that it is volatile, meaning when you shut your computer off, everything that was on that drive is gone. There are some RAM drive apps that do auto backup/restore though.