As an evolutionary update, Windows 8.1 adds numerous subtle changes to Windows 8, as well as a few major changes. So let's step through the list.

Lock screen

Starting with the lock screen, which is the first thing you see when you turn on your new PC or device, Microsoft has made a personal experience even more personal. So where you could previously customize this screen with a single photo, you can now configure a slide show consisting of photos on your PC/device or in SkyDrive. You can also access the PC/device camera, and a new "slide to shut down" feature (on modern devices only) directly from the lock screen. Yep. It works just like the lock screen on your phone.

Take a look at Hands-On with Windows 8.1: Lock Screen for more information about this feature.

Start screen

The Start screen has been overhauled fairly dramatically. There are now more tile sizes, including new Large and Small sizes (in addition to Wide and Medium), giving you more options for configuring the look and feel of this critical interface.

Tile customization is now more error-proof, with the Start screen supporting a new Customize mode so you don't inadvertently move, delete or resize a tile with an errant swipe or mouse movement.

You have more choices for background patterns, called tattoos, including some nifty animated options. And instead of a limited step of accent and background color options, you can choose from a basically infinite selection of both.

You can also choose to use the same background photo or image as your desktop, which dramatically eases the transition between that interface and the Start screen. Find out how to make this work in Hands-On with Windows 8.1: Use Desktop Wallpaper on the Start Screen.

(And be sure to check out Hands-On with Windows 8.1: Start Screen for a further discussion of this important new interface.)

The Apps view is the yin to the Start screen's yang: Where the latter is a highly customized jumping off point for your computing activities, the former is a dumping ground for all of the apps (and desktop applications that are installed on your PC/device. This interface looks and works much as it did in Windows 8, except that it's now more discoverable—a little down arrow appears if you move the mouse around, indicating that something is there—and you can sort the display by name, date installed, most frequently used or category.

Read Hands-On with Windows 8.1: Apps View for more information.

New UI and capabilities

Aside from concerns about Microsoft combining the Windows desktop with a new mobile environment in Windows 8, one of the big complaints about the initial release of that OS was that the mobile environment, Metro, was so functionally immature. So it shouldn't be surprising that Microsoft worked to fix these issues, and you can see improvements throughout the system.

The biggest change, in many ways, is a simple enough addition: The Metro-based PC Settings interface is now far more complete, and includes most of the commonly needed settings, whereas you had to fall back on the desktop-based Control Panel previously. On the downside, the newly hierarchical structure of PC Settings is often tough to navigate, and it's sometimes not clear where you're supposed to go. For example, you add new devices through PC & Devices, Devices. Unless they're Bluetooth devices: Those are added in PC & Devices, Bluetooth.

Possibly the silliest feature in Windows 8, Snap has been improved enough to be actually useful, a welcome change. Now, instead of forcing a strange 320 pixel ghetto on the side of the screen, Snap can be used in more granular increments, including a nice 50-50 split that is often automatically invoked; for example, when you open an attachment from Mail. But if you have enough onscreen real estate, you're not even limited to two side-by-side apps. You could have three or more.

And speaking of silly, Windows 8.1 actually includes honest-to-goodness help in the form of pop-up tips—comically large and impossible to miss—and a new Help & Tips app that has some nice visual walkthroughs. Very much needed, and something Windows 8 should have had a year ago. Find out more in Hands-On with Windows 8.1: Help + Tips.

Windows 8.1 also addresses another strange omission in Windows 8: It is configured, by default, to automatically update apps in the background, so everything is always up to date. This applies only to Metro apps, of course, but it's a welcome improvement.

As I noted in Hands-On with Windows 8.1: Touch Keyboard, Windows 8.1 also nicely improves the touch keyboard, which works on the desktop too, for the first time. And I spelled out some other nice changes in other articles: Full support for portrait mode (Hands-On with Windows 8.1: Portrait Mode), micro-SD, SD, and other portable storage devices (Hands-On with Windows 8.1: SD Support), and a nice new set of utility-like Metro apps (Hands-On with Windows 8.1: New Utility Apps) that furthers the maturity of that environment.

There are also new inconsistencies. Some apps continue to use partially or completely hidden app bar UIs, so you need to know to swipe from the top or bottom edge of the screen (or right-click, or type WINKEY + Z) to find and access them. Some apps provide a thin strip of an app bar as a hint that more commands are available. And some apps now just leave up the app bar, visible all the time. I realize that different apps have different needs. But I find this disparity confusing, and I suspect other users will too.

Smart Search

The new Bing-infused Smart Search functionality in Windows 8.1 is arguably this system's biggest feature. But part of the reason that it's such a big deal is that it steps away from the central functionality in Search for Windows 8. Confused? Don't be: Microsoft made the same mistakes previously in Windows Phone 8 a fact the Windows team simply ignored. So here we are.

To recap, Search in Windows 8 was a system-wide feature where you could filter a search query between apps, settings, and files. But you could also recast a search to any compatible app, which was most of them. So you could search for a term like Paris and Windows would look for an app named Paris. You could change the target of the search to other choices, including settings and files, but also individual apps. Filter to Xbox Music and it would look for music that matched that term. Filter to Photos and it would find your personal photos from Paris.

This type of centralized search functionality is an example of what I call demo-ware. That is, it looks great up on stage in a public demo. But it falls apart in real life, especially the searching within apps bit. Turns out most users don't think that way or wish to use search like that. If they want to find a song called Paris, they will load the Music first. And when they're looking for their photos, they open Photos first.

As noted previously, Microsoft made this same mistake in Windows Phone years earlier and then fixed it, again years earlier, in a subsequent release of that OS. So I was amused to see Microsoft make the same mistake in Windows 8. And now that they're fixing it in Windows 8.1, I'm not surprised. Just stupefied they ever did it in the first place.

The replacement for centralized search, by the way, is app-based search. That is, the built-in Metro apps now include their own search functionality—again, just like what happened earlier in Windows Phone—and unlike the Search charm, these UIs are generally visible and discoverable.

With that bit of order restored, the system-wide Search charm could have continued on as a way for users to find apps, settings and files, and I don't think many people would have complained. But give Microsoft some credit: It turns out they had a grander vision for this functionality. And in Windows 8.1, the firm has integrated Bing search directly into Search, providing users with a single UI for searching both their local system and the web.

Now, this functionality may eventually prove to be as useless as centralized search, and if you don't like it, heads-up, you can disable it. But the results are often very nice. Consider the Paris example from above. When I search for this term on my own PCs, I see the following.

What you see here are results that contain my own documents, music and photos. A weather report, which links to the Weather app. A way to visit Paris in Maps. A way to find out more about Paris in the Travel app. And then beautifully presented web results, including photos, useful web results, and Windows Store apps.

If you don't want or need this kind of presentation, you can filter the search up front to display only settings, files, web images or web photos. But I'm curious to see whether people like the new search.

In the meantime, check out Hands-On with Windows 8.1: Smart Search for a closer look at this interesting new feature.

Desktop

Desktop users have not been forgotten.

First, and most prominently, the Start button is back where it belongs on the left side of the taskbar. Check out Hands-On with Windows 8.1: Start Button for more info.

Those with less than positive thoughts about Metro can also optionally fully or partially disable some Metro features such as the Switcher, Charms, and even the Start screen: Instead of navigating to the Start screen, you can go to the more Start menu-like Apps view when you click the Start button. Yes, it's still a full-screen experience. But you can configure it to display desktop applications first. It's not horrible.

Best of all, you can even boot directly into the desktop now. Check out Hands-On with Windows 8.1: Boot to Desktop for the details.

Microsoft claims to have solved the problem with using the Windows desktop on very high DPI screens: It supports the ability to scale the display automatically and to handle different screens differently; that is, you can configure the tiny screen on a Surface Pro to 125 or 150 percent scaling, but configure a larger attached screen to 100 percent scaling. I wrote about this capability in Hands-On with Windows 8.1: Desktop Display Scaling, but the truth is that this is one area where I'm not seeing the results I expect. Clearly, it's supposed to work properly, so I will keep trying.

File Explorer has been upgraded in ways both useful and troubling. In the useful department, File Explorer now presents a simpler new default view, called This PC, in place of the older Computer and My Computer views. (See Hands-On with Windows 8.1: This PC for more information.) And you can see the beginnings of a drive letter-free future here, too: Certain device types, like phones and other digital devices are no longer displayed with drive letters.

But there are some troubling changes happening, too. The libraries system from previous Windows version is being deemphasized, and no longer appears by default in File Explorer; indeed, you really have to hunt to find these virtual locations. But libraries are curiously used by many Metro apps to populate the content they display; for example, the Photos app uses your Photos library almost exclusively.

Finally, there have even been small and useful changes to what I call the Power user menu, which is available from both the desktop and Metro: See Hands-On with Windows 8.1: Power User Menu for what's new.

SkyDrive

SkyDrive is now more deeply integrated into the operating system, for example, and where Windows 8 provided a certain measure of settings sync between PCs and devices and required you to find and install a desktop application to sync SkyDrive-based documents between the cloud and your PCs and devices, Windows 8.1 goes further: There are far more settings that can sync—including, optionally, Start screen layouts and tiles—and document sync is built right-in.

As I wrote in Hands-On with Windows 8.1: SkyDrive Integration, this functionality is one of the biggest changes in Windows 8.1. It's worth knowing about.

There is also a separate SkyDrive mobile app, as before, but with two key differences. You can use this app to navigate both your local PC/device—called This PC—and SkyDrive, so it's sort of a file explorer app too. And because document sync is built right-in now, you can use this app to mark folders or files for offline use. (You can do this from File Explorer in the desktop too.)

In Hands-On with Windows 8.1: SkyDrive App, I take a closer look at this newly updated app.