The Protected RAM Filesystem is a persistent, non-volatile RAM-based filesystem, with persistence meaning that the filesystem survives intact across a system reboot or power cycle.
The code for this was developed by Monta Vista. This technology is integrated in the CELF source trees (for versions 031030 through (at least) 040304), and is available by enabling the option "Persistent and Protected RAM file system support", in the "File systems" menu of kernel configuration. (The option is CONFIG_PRAM_FS).
/\ Note that the version of PRAMFS in the CELF source tree are likely out-of-date, as of April, 2004.
/\ Also, please note that Monta Vista has a patent pending on this code, but is licensing the patent freely for use in GPL software. The patent license is included in a comment at the top of every file in the pramfs system. For example, to see the license grant, look at the file fs/pramfs/balloc.c.