We started planning Windows 8 during the summer of 2009 (before Windows 7 shipped). From the start, our approach has been to reimagine Windows, and to be open to revisiting even the most basic elements of the user model, the platform and APIs, and the architectures we support. Our goal was a no compromise design.

This is an ambitious undertaking—it involves tools, APIs, languages, UI conventions, and even some of the most basic assumptions about a PC. For example, how do you isolate applications from each other, or prevent applications from stealing all your battery power? How can installing (and removing) apps be as quick and painless as changing the channel on the TV? How do you attract the broadest set of developers possible to a new platform? How do you build a touch-first interface with a unique point of view?

When we showed the first demos of Windows 8, we introduced our new Metro experience—fast and fluid, immersive, beautiful, and app-centric. We are certain that as we show you more in the coming months you will see just how deeply we have reimagined Windows. Metro style is much more than the visual design as we shall see.

the role of the Windows desktop is clear. It powers the hundreds of thousands of existing apps that people rely on today, a vast array of business software, and provides a level of precision and control that is essential for certain tasks. The things that people do today on PCs don’t suddenly go away just because there are new Metro style apps. The mechanisms that people rely on today (mice, physical keyboards, trackpads) don’t suddenly become less useful or “bad” just because touch is also provided as a first-class option. These tools are quite often the most ergonomic, fast, and powerful ways of getting many things done.

We knew as we designed the Windows 8 UI that you can’t just flip a bit overnight and turn all of that history into something new.

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You get a beautiful, fast and fluid, Metro style interface and a huge variety of new apps to use. These applications have new attributes (a platform) that go well beyond the graphical styling (much to come on this at Build). As we showed, you get an amazing touch experience, and also one that works with mouse, trackpad, and keyboard. And if you want to stay permanently immersed in that Metro world, you will never see the desktop—we won’t even load it (LITERALLY THE CODE WILL NOT BE LOADED) unless you explicitly choose to go there! This is Windows reimagined.

But if you do see value in the desktop experience—in precise control, in powerful windowing and file management, in compatibility with hundreds of thousands of existing programs and devices, in support of your business software, those capabilities are right at your fingertips as well. You don’t need to change to a different device if you want to edit photos or movies professionally, create documents for your job or school, manage a large corpus of media or data, or get done the infinite number of things people do with a PC today. And if you don’t want to do any of those “PC” things, then you don’t have to and you’re not paying for them in memory, battery life, or hardware requirements. If you do want or need this functionality, then you can switch to it with ease and fluidity because Windows is right there. Essentially, you can think of the Windows desktop as just another app.

Windows 8 brings together all the power and flexibility you have in your PC today with the ability to immerse yourself in a Metro style experience. You don’t have to compromise! You carry one device that does everything you want and need. You can connect that device to peripherals you want to use. You can use devices designed to dock to large screen displays and other peripherals. You can use convertible devices that can be both immersive tablets and flexible laptops.

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. 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. If you’re not familiar with hibernation, we’re effectively saving the system state and memory contents to a file on disk (hiberfil.sys) and then reading that back in on resume and restoring contents back to memory. Using this technique with boot gives us a significant advantage for boot times, since reading the hiberfile in and reinitializing drivers is much faster on most systems (30-70% faster on most systems we’ve tested).

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. For those of you who prefer hibernating, this also results in faster resumes from hibernate as well.

One thing you’ll notice in the video was how fast the POST handoff to Windows occurred. Systems that are built using Unified Extensible Firmware Interface (UEFI) are more likely to achieve very fast pre-boot times when compared to those with traditional BIOS. This isn’t because UEFI is inherently faster, but because UEFI writers starting from scratch are more able to optimize their implementation rather than building upon a BIOS implementation that may be many years old. The good news is that most system and motherboard manufacturers have begun to implement UEFI, so these kinds of fast startup times will be more prevalent for new systems.

Of course, there are times where you may want to perform a complete shutdown – for example, if you’re opening the system to add or change some hardware. We have an option in the UI to revert back to the Windows 7 shutdown/cold boot behavior, or since that’s likely a fairly infrequent thing, you can use the new /full switch on shutdown.exe. From a cmd prompt, run: shutdown /s /full / t 0 to invoke an immediate full shutdown. Also, choosing Restart from the UI will do a full shutdown, followed by a cold boot.

With the introduction of OS X Lion, Apple gave us a glimpse at what a post-PC operating system might look like, and now Microsoft's gone and pushed that idea to the limit. If Cupertino's latest was a tease, than Windows 8 is full frontal. And we have to admit, we like what we see. Sure this may not be the final build, or anywhere near it, but for whatever flaws it may have, the UI being offered in this developer preview is really something special. Time will tell if the "one ecosystem to rule them all" approach will catch on, but for now it's time to give props where props are due -- at least until we can get our hands on a final build.