What is a ram disk and how does it work?

I have been using AMD's RamDisk on two of my workstations for the past several months. I love it. It creates a disk made up of some of your normally unused memory (in which you set it-I have mine at 16GB). Speeds are over 9000MBs on my system. I use the disk for storing whatever I am working on at the time (photos, videos). You can use it for other things to, like cache storage. You can try the "small" version of the software for free.