Building Windows 8: Fast boot times with "hybrid boot"

In today's installment on the Building Windows 8 blog, Microsoft described the new "hybrid" boot mode that will be included in Windows 8. According to Microsoft's claims, the new algorithm will result in 30 to 70% faster boot times compared to a traditional "cold" boot in Windows 7.

The need for a clever way to speed up cold boot times was made evident by telemetry data from Windows 7, which demonstrates the large percentile of Windows 7 users that insist on shutting down their machines:

Clearly there were users who preferred shutting down to minimize energy consumption that is required for sleep modes. On the other hand, there are also users that prefer an almost "instant-on" resuming experience that sleep offers. And finally, there are the small number of users in-between who enjoy both with hibernation.

However, hibernation requires a large amount of hard disk space that scales according to the amount of RAM a user has installed on their computer. In addition, some users would also prefer a clean start to their current working sessions upon a login.

The new Windows 8 "hybrid boot" takes advantage of both shutting down and resuming from a hibernation file. Microsoft describes the Windows 7 shutdown process as follows:

  1. The user initiates a shutdown by selecting “shut down” from the Start menu, or by pressing the power button; or an application initiates shutdown by calling an API such as ExitWindowsEx() or InitiateShutdown().
  2. Windows broadcasts messages to running applications, giving them a chance to save data and settings. Applications can also request a little extra time to finish what they’re doing.
  3. Windows closes the user sessions for each logged on user.
  4. Windows sends messages to services notifying them that a shutdown has begun, and subsequently shuts them down. It shuts down ordered services that have a dependency serially, and the rest in parallel. If a service doesn’t respond, it is shut down forcefully. ‪‬
  5. Windows broadcasts messages to devices, signaling them to shut down. ‪‬
  6. Windows closes the system session (also known as “session 0”).
  7. Windows flushes any pending data to the system drive to ensure it is saved completely.
  8. Windows sends a signal via the ACPI interface to the system to power down the PC.

The new "hybrid boot" only goes as far as terminating user sessions, and opts to hibernate the kernel and device driver data for the next boot. The boot technology works hand in hand with EFI technology, which works hand in hand with Windows to enable fast boot. EFI replaces the aging BIOS that is on most current PC's, and Windows 8 fully supports the technology.

It should be noted that a "clean" shutdown will still be offered as a UI-configurable option, or by invoking "shutdown /s /full /t 0" from the command line in Windows 8. Rebooting the system will also trigger a clean shutdown to accommodate installers that reboot the system due to a driver or system file change.

So how do these changes stack up across many existing Windows 7 PCs? The changes are universally positive:

An example is seen in an impressive video posted by a Microsoft program manager. The laptop shown in the video is using EFI boot technology:

These impressive results will be made clear to developers and enthusiasts alike in the upcoming BUILD Conference in Anaheim, which kicks off next Tuesday the 13th. Neowin will be providing live coverage of the four-day event.

Image Credit: Building Windows 8 blog; stock photo from sxc.hu

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