Because they are made of normal RAM, RAM disks lose their contents once the computer is turned off. To use a RAM disk, therefore, you need to copy files from a real hard disk at the beginning of the session and then copy the files back to the hard disk before you turn the computer off. Note that if there is a power failure, you will lose whatever data is on the RAM disk. (Some RAM disks come with a battery backup to make them more stable.)

A RAM disk is also called a virtual disk or a RAM drive.

Driving for Performance: RAMDrive and SMARTDrive
Paper containing information on DOS RAM drive performance and configuration.