RAM drive
A RAM disk is a segment of active computer memory, RAM, which is being used as if it were a disk drive. Access times are greatly improved and durability of data through power loss is completely absent. RAM disks are great places to store temporary data or to hold uncompressed programs for short periods.
A proper disk cache in the operating system will usually obviate the performance motivation for a RAM disk; a disk cache fulfills a similar role (fast access to data that is notionally stored on a disk) without the various penalties (data loss in the event of power loss, static partitioning, etc.). RAM disks are, however, indispensable in situations in which a physical disk is not available.
Another way to use RAM to store files is the temporary filesystem. The difference between temporary filesystem and a RAM disk is that the RAM disk (/dev/ram0 etc.) is fixed-sized and acts like a disk partition, whereas the temporary filesystem (/dev/shm; in Source Mage GNU/Linux also /tmp) grows and shrinks to fit the files put on it.