I'm guessing the system must effectively "checkpoint" your work regularly and sync to disk to avoid partially saving a state and corrupting the data.

This isn't terribly different from working on a memory mapped file except that it also saves the ephemeral state of the running program so it can be restored. But I still don't understand how it's not going to be horribly slow when you start your program and the first thing it does is allocate 4GB of memory for its workspace. Synching all of that data to disk is a massive undertaking, and this isn't an uncommon use case, people start virtual machines all of the time.

And paging is slow as balls. That's what this whole article is about, modern machines are unusable when they start paging.