Is there a RAM-resident FS in Berkeley distribution?

[Tom Chmara]

I've heard reference (no, I don't remember where) to a ram-resident
filesystem either distributed as part of the BSD O/S or built as
part of the installation procedure (in either case it's used to bring
BSD up, rather than as a permanent ramdisk).  I can't find any mention
of anything like this in the sources (4.2 or 4.3).  Could anyone help
me with a pointer?  Where am  I not looking?  Or is it possible that
I'm just cracking under the strain and nothing like this really exists?
I've found mention of the swap partition F/S, but I don't think that's
what I want.
	Thanks for your time...
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