I am sure that you have, without a doubt, noticed that rebooting takes much longer than starting up from a shut down.
When you "shut down" your PC, it saves a copy of they system state / driver state to the HDD, and boots from that, bypassing starting up all devices and reloading drivers from scratch.
I don't know all of the technical details, but you can probably do a search.
This causes some confusion when looking at the Task Manager. If you look in task manager, under CPU, it might show that the system has been up for 8 days, which is misleading. This shows that the PC really doesn't "shut down". Sure, the power is cut off, but it is a kind of immediate hibernation.
The system up time only resets to 0 when you do a reboot, because all system data is discarded and the system will boot up from scratch, hence taking longer to get to the start screen.
so I've got Intel Core 2 Duo @2.93 @2.13 GHz
8 GB of Ram
DDR2 Gigabyte Motherboard
2 HDDs each 500GB (internal) Serial ATA
and my full boot from the power button to the windows 8 desktop takes about 12~14 seconds.
Restarting takes 24~26 Seconds.
The Boot Animation takes 2.13 Seconds.
How come I've got this speed?
NOTE: my C:\ is on the 1st HDD , and is mirrored to the 2nd HDD.