OS News reports Microsoft has given Windows 8 a faster bootup time by hibernating the kernel session rather than closing it when shutting down the system:
In Windows 8, things are done differently. All user-related stuff is still properly shutdown like before, but everything related to the kernel goes into hibernation. "Now here's the key difference for Windows 8: as in Windows 7, we close the user sessions, but instead of closing the kernel session, we hibernate it," Aul explains, "Compared to a full hibernate, which includes a lot of memory pages in use by apps, session 0 hibernation data is much smaller, which takes substantially less time to write to disk."
It also takes substantially less time to boot. "It's faster because resuming the hibernated system session is comparatively less work than doing a full system initialization, but it's also faster because we added a new multi-phase resume capability, which is able to use all of the cores in a multi-core system in parallel, to split the work of reading from the hiberfile and decompressing the contents," Aul adds, "For those of you who prefer hibernating, this also results in faster resumes from hibernate as well."