The last version of Android to be released, 4.1, code-named "Jelly Bean," was only an incremental bump over the major 4.0 release ("Ice Cream Sandwich"). But that little bump made a big difference. Android became more or less fully realized with Ice Cream Sandwich, but Jelly Bean brought a level of polish and maturity that the platform previously lacked.

The biggest improvement for the end-user experience was "Project Butter," the name given to a group of adjustments vastly upgrading Android's responsiveness to touch input. These included adding triple buffered graphics rendering and maximizing the CPU's clock speed briefly whenever the screen is touched (there were also a few other underlying architectural improvements). Taken together, the tweaks made overall performance much more consistent in Jelly Bean. Before, Android's interface was capable of smoothness on sufficiently fast hardware (see our Optimus G review for evidence of that), but Jelly Bean brought smoothness even to older hardware like the Motorola Xoom and first-generation Kindle Fire. Using Android finally felt as good as using iOS or Windows Phone.

Now, only four months after Android 4.1 was released into the wild, the mobile operating system is getting another incremental bump. Android 4.2 carries the same "Jelly Bean" code-name as 4.1. It doesn't bring any drastic changes to the operating system and, given its quick turnaround, no one really expected it to. However, it introduces enough new features to keep Android a healthy contender in the vicious smartphone and tablet markets.

Multiuser support

On tablets, Android 4.2's biggest innovation is multiuser support. These devices are often shared between family members, but a way to keep everyone's chocolate out of everyone else's peanut butter has been generally lacking among tablets since the iPad popularized the form factor 2010. With Android 4.2, different users will be able to configure their own home screens (along with backgrounds, apps, and widgets) and application settings. Finally, there's a way to allow children to play games on the tablet without accidentally erasing all of your work e-mail.

The feature will only be coming to tablets at this point, however—speculation on exactly why has ranged from the innocuous (tablets are more likely to be shared than smartphones) to the litigious (Nokia has its name on a patent that may prevent the feature's implementation on phones). Google informs us the feature will also be coming to 7-inch tablets, so the Nexus 7 should gain multiuser support as soon as its 4.2 update drops.

Currently, we have as many questions as you do about how Android's implementation works: what are its storage requirements? What are its memory usage requirements? Can apps be shared between accounts? Are usernames and passwords set locally, or can you sign in with Google accounts as in Chrome OS? What security measures prevent one user from getting notifications and other data intended for another user? Unfortunately, we don't have any answers at the moment, because the Android 4.2 build that enables multiuser support won't be delivered to Nexus 10 tablets before they begin shipping on November 13. At that point, we'll install the update and publish a follow-up report.

Notifications

Pull-down notification panels have almost always been a part of the Android package. Apple even took a page from Google's playbook by introducing pull-down notifications in its iOS 5 update. Notifications are the gateway to the Android brain, enabling users to keep an eye on what their handset is doing. They have proven to be an unobtrusive way of delivering essential information.

In Android 4.1, Google enhanced notifications panels by making more of them expandable and enabling users to work within them without having to click too many times. Users are no longer just checking to see that someone tweeted them. Instead, they can see exactly what was tweeted, and then reply by launching the Twitter application from the pull-down shade. Notifications aren’t deleted unless they’re swiped away or dealt with, so you don't have to worry about missing something.

Now in 4.2, Google has followed OEMs like Samsung and LG by including a Quick Settings menu. As the snappy name indicates, Quick Settings allows users instant access to the most frequently changed settings—brightness, connecting to Wi-Fi, checking data usage, displaying battery life, toggling Airplane mode or Bluetooth, and initiating the wireless display. (That last one is part of Android 4.2's Miracast feature, which you can read more about on page three.)

Google previously hid these settings behind another screen, requiring users to tap twice before they can get to it from the Notifications shade. The ability to adjust the screen brightness in a pinch will save a lot of eyes from blinding white screens, though we prefer the way manufacturers like Samsung and LG have kept settings part of the pull-down menu. Google still including the power control widget for users to affix to their Home screens if the double-tap or double-finger swipe is one too many actions.

Both the Notifications and Quick Settings panels are now also accessible from the lock screen of a phone or tablet without an unlock PIN or password. For security reasons, this is disabled on devices with passcodes however. It's a nice touch if you're not locking your screen, though you obviously run a huge risk of data theft when you use a phone or tablet without a password. We recommend that you ignore this feature entirely in favor of securing your data.

New 10-inch tablet user interface

Android 4.2, at least on the Nexus 10, formally retires the Android tablet UI originally introduced in Honeycomb (Android 3.0). This interface survived with few functional tweaks all the way up until Android 4.1, as we saw when we installed the first Jelly Bean update to a Motorola Xoom tablet.

This interface shared many features in common with the phone and 7-inch tablet UI on other Android devices, but it moved things around a bit. The navigation buttons were still stored at the bottom of the screen, but in the lower-left corner rather than in the center. Notifications were accessed by swiping up from the lower-right corner of the screen rather than down from the top. The application switcher appeared on the left side of the screen rather than taking up the whole thing. There were a few other changes, but these were the biggest—the end result was something with the same features as an Android phone, but requiring different actions to access common features.

The Nexus 7 made the jump to a more phone-like user interface, and the Nexus 10 follows suit. The new user interface makes some tweaks however, since widescreen tablets will most often be used in landscape mode. But the basics work just as they do on the Nexus 4 and Nexus 7: navigation buttons centered in the middle of the screen, a persistent row of applications just above that, and notifications at the top of the screen. There are still some differences between the 7-inch and 10-inch tablet interfaces, all of which are easier to show than to tell.

The notification center also acts slightly different on a 10-inch tablet than on a phone—the standard notification center is accessed by swiping down from the top on the left half of the screen, while the new quick settings menu is accessed by swiping down from the right half. On the Nexus 4 (and other Android phones, when and if they receive an Android 4.2 update), the quick settings menu is accessed via a button in the normal notification center or by swiping down from the top of the screen with two fingers.

The experience of actually using a 10-inch Android tablet doesn't change tremendously with the new UI. The persistent row of applications across the bottom of the screen slightly reduces the amount of vertical space available for widgets. This may be a worthwhile sacrifice to make—otherwise, applications look and run just as they did before.

Some may argue that the new UI isn't the best use of a 10-inch tablet's real estate, but this strikes us as a concession to usability and consistency on Android's part. The old 10-inch UI took familiar elements from the phone UI and put them in unfamiliar places. With the new UI, anyone who picks up and uses a Nexus 7 or a Nexus 4 will automatically be able to pick up and play with a Nexus 10 without needing a re-learn anything. This is a small but important step in selling Android users on the larger tablet. After all, an iPad looks and operates mostly like a blown-up version of the iPhone and iPod touch. In the long run, this certainly helped keep Apple consumers comfortable as they move between devices.

But the biggest question: will an Android 4.2 update to existing 10-inch tablets change the user interface to the new phone-style or allow partners to continue using the old UI to prevent user frustration? Having something you use every day suddenly change can be jarring. But even if it's no longer officially supported by Google, it's a fair bet third-party launchers will be able to re-enable it if you really prefer.