To create a "RAM based directory" is more of a task for an operating-system than a program. Really, you'd need to mount a new type of file-system (there may be support for some existing RAM-disk-based file-system in your OS or not).
in reply to in memory files in 5.6.1
What you have the option of doing inside your program is to not go to the file-system at all, which is what various perl constructs such as IO::Scalar and the similar builtin functionality in 5.8 do.
Not an editor command: Wq