Persistent Storage notes
------------------------

Goals:
 1. Simplify using and programming the system
 2. Keep data committed do disk as much as possible, for reliability

"Test cases":
 1. Creating a new object: Create in RAM and mark "unsaved"

 2. Modifying an object: Mark "unsaved"

 3. Not enough RAM: Remove oldest "saved" object from RAM.
    Still not enough? Save oldest "unsaved" object and remove it from RAM.

 4. To access an object: Ask the Object Manager

 5. Object needed, but not in RAM? Load it.

