Did you know that an SSD-equipped Windows 8 PC can boot up in under seven seconds? Watch the video below if you don't believe it, Microsoft has really optimized the hell out of the startup operations of its next OS — although that has come at a somewhat amusing cost: you no longer get enough time to interrupt the boot process. The current ability to press F8 while your PC is powering up and the ever-familiar BIOS menu prompt of "Press F2 to enter setup" will both be missing from Windows 8 computers, simply because the hardware and software have advanced to such an extent as to leave users with too little time to access them.
Chris Clark, program manager at Microsoft's User Experience team, notes in a Building Windows 8 blog post that users are now left with a tiny 200ms window in which to signal to a booting PC that they want to interrupt what it's doing and make changes to its boot setup. A new solution is clearly needed and Microsoft's response has been trifold: firstly, all the various settings that may have been distributed across troubleshooting, developer, and startup menus are now being consolidated into one boot options group; secondly, that menu will appear automatically anytime something prevents Windows from booting up correctly; and thirdly, Microsoft is making it easy to access said repository of options by giving you multiple ways of bringing it up even when there's nothing wrong with the PC.
In short, while you'll lose the ability to alter boot and BIOS settings before the OS is up and running, you'll still be able to do so once you're inside it via the Advanced startup section of the General options menu, and if you can't reach that point, the bootup settings will automatically show up for you, recognizing that they're needed. Now if you want the long, fully detailed version, check out Chris' comprehensive writeup over on the MSDN blog.
One final note of import: all of the changes discussed by Chris Clark relate specifically to newer PCs with UEFI BIOS. As he notes, "legacy hardware that was made before Windows 8 will not have these new UEFI-provided menu features (booting to firmware settings and booting directly to a device). The firmware on these devices will continue to support this functionality from the POST screen as it did in the past."