Puppy Linux is a small, but full-featured Linux distribution. Puppy boots into a ramdisk and loads into RAM.

Puppy Linux is a small, but full-featured linux distribution. Puppy boots into a ramdisk and loads into RAM. Puppy Linux can boot off a flash card or any USB memory device, CDROM, Zip disk or LS/120/240 Superdisk, floppy disks, internal hard drive.
Website: http://puppylinux.org
Distrowatch: http://distrowatch.com/table.php?distribution=puppy
Wikipedia: http://en.wikipedia.org/wiki/Puppy_Linux