Unless you have to, it is many times advantageous to “warm boot�, or rather warm reboot, Windows. In a warm reboot, Windows restarts, but the computer doesn’t, skipping the whole pre-Windows boot screen/BIOS/startup sequence. You can easily specify a warm boot in both Windows XP and Windows Vista. Just hold down SHIFT on your keyboard before clicking “Restart� in Vista, or before clicking OK in the restart dialog in XP. Enjoy the extra 20 seconds!

Technically, the use of the term “warm boot� is a bit misused here, but the small amount of time saved by not re-running the BIOS can be worth it.

Microsoft, Windows XP, Windows Vista, Tips and Tricks, Knowledgebase

Source:? InsideMicrosoft