dev.

I just noticed one nifty feature of my MacBook Pro: “automatic” deep sleep.
When you close the lid of your MB(P) and the white light on the front begins to flash slowly, it has suspended. As soon as you open it, it will wake up and fetch its session data from ram. That takes just a few seconds, and then you are good to go.
But what happens if the Mac loses power while suspended? All data stored in ram would be lost, and a normal reboot would be required. So a “suspend to disk” seems to be a better choice – but a wake-up would be pretty much slower.
Mac OS X is pretty clever: it seems to go for “suspend to ram” by default, but persists your session to disk as well. So you get a fallback (“wake from disk”) whenever the Mac has been suspended, but “wake from ram” failed.