It was invented for Windows Phone 7 but will be the new look for Windows 8. The Metro user interface is radically different, with no windows, frames, menus, or other UI elements on the screen: just the content itself.
It's also promised to be gesture-oriented, though it will work with a mouse and keyboard as well.
Windows 8 is six to twelve months away, but this week Microsoft released a developer preview that shows off some of the forthcoming OS.
Much is still not working, and everything is subject to change, but here's PC Advisor sister site InfoWorld's first look at the new UI for Windows you may be using in 2012 or 2013.
See also: Microsoft Windows 8 review
Setting up Windows 8
When you run the Windows 8 installer, you get a preview of the spare Metro look and feel in the setup options that appear.
The use of large text and significant open space in the Metro UI – designed so that it works on the smaller screens of tablets – means you'll likely have to use several screens in Windows 8 where you might use just one in Windows 7 (or in Mac OS X or, ironically, in the clean but still denser UI of the iPad's iOS).
The welcome screen
Windows 8's welcome screen can be quite puzzling: What do you do, given its lack of buttons and menus? The answer is to roll up the screen to expose the login page, where you enter your Windows Live ID or other username and password. You can also shut down or restart Windows 8 from that login screen.
The Start screen
When you log into Windows 8, there's no longer a desktop. Instead, you get the Start screen that has tiles for Internet Explorer, Windows Explorer, and various apps and widgets you can pin to it. The idea is that the Start screen is your central dashboard for switching among tasks.
The Start screen is expandable, so you'll likely need to scroll horizontally to see more of your tiles. Like Mac OS X Lion, Windows 8 by default shows no scroll bar until you start moving your mouse. (If you have a touchscreen PC or tablet, you just swipe to scroll; there is no scroll bar on gesture-savvy devices.)
Customizing the Start screen
You can customize the Start screen by dragging tiles to whatever position you desire. You can also change the size of the tiles between square and rectangular using the application bar. The app bar is also where you remove (unpin) tiles and add new ones.
Introducing the app bar
The application bar contains the controls a developer wants users to have for the specific app. It is very similar to the set of options that developers provide to users via Android's Menu button.
The app bar is hidden by default. Press the Windows key to open it; if you have a touchscreen device, just swipe up from the bottom of the screen.
A related interface item is called the charm pane, which displays at the right side of the screen when a user swipes in from that side; it contains OS-wide features such as share and search.
The Metro UI tries to reduce interruptions to the user for specified applications (similar to what Apple has planned for iOS 5).
An example: Non-urgent notifications of new mail appear for a few seconds at the bottom right of the screen.
Applications also display notifications above the app bar, as shown here; these notifications too disappear after a few seconds if not opened by clicking or tapping.
Optimized for widgets
The Metro UI's spare, open look is optimal for widgets. Microsoft says more complex apps such as Office and Photoshop that make extensive use of floating panels, menu items, and ribbon bars should use such Windows 7-style UI elements instead.
You can think of Metro as the overlay UI, with the Windows 7 UI lurking underneath for use when needed on Intel x86-based devices.
What's unclear is how this will work on Intel x86-based tablets, where the highly dense Windows 7 interface is not likely to be easily interactive via touch.
Microsoft's own gesture gurus, for example, recommend that objects be between 7mm and 11mm in size, plus 2mm of space for effective touch usage (7mm results in a miss 1 percent of the time, whereas 11mm results in a miss 0.01 percent of the time).
That limits the number of buttons to between 16 and 24 horizontally – a fraction of what many apps now display.
(ARM-based devices can't run legacy Windows apps, so they'll have only Metro-style apps to worry about.)
Contextual menus remain
Right-clicking still opens a contextual menu in Windows 8, though as you can see from this screen, they're bigger and thus less likely to have as many options in them as "legacy" Windows applications.
The familiar Windows Explorer
The Windows Explorer (accessed from a tile on the Start screen) is the familiar one from Windows 7 – so far, it's not been Metroized.
Given what Microsoft has shown about Windows 8 file management, virtualization, and networking functions, they may well retain the Windows 7 look even in the final version of Windows 8.
But because ARM-based devices can't run Windows 7-and-earlier code, it's not clear how ARM-based devices will implement Windows Explorer.
Windows 8's control panels, accessed via the Start screen, have the same spare look as any other Metro element; be prepared to scroll down to see more options to configure and sideways to see the specific settings for a selected control panel. (You can also click the control panel name.)
When you select a control panel, the Metro UI slides the view to the right to display the specific options, as shown here for notifications.
Windows 8's settings for devices work just like control panels do, with the same spare interface.
Not all device settings are available through the Metro UI's controls. In that case, Windows 8 takes you to the Windows 7-style Device Manager, shown here.
The same is true for control panels: The standard Windows 7 UI is available for them as well, if your device runs on an Intel x86 chip.
Windows Explorer, reloaded
Explorer in Windows 8 sports a new look that includes the addition of the ribbon along the top. The purposes behind the new design, according to Microsoft, is to optimize file-management tasks by exposing more commands in logical groupings while bringing back some of the requested features from the Windows XP era.
A ribbon runs through it
Borrowing from Office 2010's design, Windows 8's ribbons are designed to expose the most frequently used commands for such tasks as file sharing, as well as to adjust the appearance of windows.
There are also dynamic ribbons for library tools, picture tools, and disk tools. Ribbon loathers, take heart: Ribbons can be hidden.
Put it on my Home tab
Windows 8's Home tab ribbon prominently presents all of the platform's core file management tasks, including Copy, Paste, Delete, Rename, Cut, and Properties.
Microsoft has taken pains to expose three popular yet sometimes overlooked features found in previous Windows iterations: Move To, Copy To, and Copy Path.
The latter is useful for pasting a file path into a file dialog or for sharing a link to file on a shared server.
Admin-friendlier File menu
The File menu provides quick access to opening new Explorer Windows, accessing shortcuts, and changing folder and search options.
Microsoft added a couple of nifty new commands to the menu: Open Command Prompt and Open Command Prompt as Administrator. Both launch a command prompt with the path set to the selected folder.
Detailed file copying
When copying or transferring files, Windows 8 users are presented with a single window that includes information about each process, including a throughput graph and estimates of how long the transfers will take.
Better conflict resolution
Windows 8, like previous versions of Windows, alerts users when they try to move files to a destination that contains the same type of files of the same names.
This time, though, Microsoft has made it easier for users to determine the differences between the conflicting files so that they can make a better-informed decision.
Boxes, little boxes
As an alternative to the traditional Windows Explorer UI, Windows 8 lets users opt for what Microsoft dubs a Metro-style UI.
Reminiscent of Windows Phone 7's interface, this interface is designed to let users take advantage of Windows 8's touchscreen capabilities for, say, forthcoming Windows 8 tablets.
Hyper-V turns 3
Windows 8 will come with Hyper-V 3.0 built-in, which could mean big things for Windows management. For example, users could run XP, Vista, Windows 7, supported Linux apps, and maybe even Windows Phone 7 apps in the same environment.
Also, third-party PC-management tools could take advantage of Hyper-V client systems for easier deployment, update, and repair of PCs.
VHDs made easy
Windows 8 brings improved support for virtualization. Among the added features: easier access to VHDs (virtual hard disks), à la Hyper-V and Virtual PC.
Windows provides a virtual drive letter pointing to the volume within a VHD. A user can work with the VHD as though it were any other file storage on his or her system.
Snappier ISO access
Windows 8 gives users the ability to directly use ISO files (or ISO images) without a physical CD-ROM or DVD drive. Rather, users can, on the fly, easily create "virtual" drives from which to access data.
The process entails choosing the ISO file, then double-clicking or clicking Mount. Windows creates a new drive letter for the virtual drive, from which the ISO file is accessible.
There's also the Eject command to make the drive disappear when you're done with the ISO file.