Persistence in computer science refers to the characteristic of state that outlives the process that created it. Without this capability, state would only exist in RAM, and would be lost when this RAM loses power, such as a computer shutdown.

Cobalt currently uses binary persistence for saving and restoring islands (pools of data and state). 

The xml format was specifically built by Qwaq to handle the problems with loading/saving spaces and their tframes. The old approach that persisted  whole islands using ImageSegments works for syncing and crash protection, but fails on the othe major use case, which is loading a space from a *template* or into existing spaces. Biggest problem with image segments is they gove you a space with the the same unique identifiers. This causes conflicts as the rest of the system assumes that you only have one island running at a time with a given island ID. There is also the potential for conflicts in the ID's assigned to frames inside the island, though that is less likely to be an issue right now (probably will be later).