Usually the configuration stays the same, though - why not a way for the user to indicate when it has? Hold down an awkward combination of three far-flung keys

Usually the configuration stays the same, though - why not a way for the user to indicate when it has? Hold down an awkward combination of three far-flung keys while booting, the BIOS wakes up and checks every device plugged into it, otherwise it just pulls it in from a cache. (And how much does the average computer's config change? How many users never change a single part of the hardware configuration of their computer for its entire lifetime? A hobbyist who built their own might swap out CPU/GPU/drive/ram/etc, but how many people upgrade their laptops in any way?) Get all that backup stuff spun up. Save the state of the entire computer the same way you're saving a hibernation snapshot. Next boot, just pull that snapshot up. Something makes that snapshot crash? Reset and run the slow boot, either because the system caught this, or because the user held down the "invalidate bootup snapshot" chord. Although realistically I never reboot my computer any more unless I'm doing an OS upgrade anyway. It's all just "sleep" and "wake up" nowadays for me, so I don't care if bootup adds a minute or two to the end of the half an hour or so my computer spent downloading the update and applying it. Maybe a cold boot just isn't worth optimizing any more.