"Defendants consider it [main memory] to mean "working memory"....or the flash totally replacing RAM.

Plaintiff considers the flash to be "storage memory"....with RAM resource in front of it."

Exactly, and that's why the phrase itself is the problem. The whole idea behind claim construction is to make sure that the claims are construed in such a way that the court can make an informed, just decision. And in order to do that the terminology must be clear and unambiguous.