Screenshot from Stephen Shankland/CNET

Google plans to release an early version of its upcoming Android operating system, Android L Preview, on Thursday.

The software will be available for those with Google Nexus 5 smartphones and Nexus 7 tablets, Android user-interface engineer Chet Haase told programmers Wednesday during a session on the new operating system at the Google I/O conference in San Francisco. It'll be available at the Android developer site, he said.

"That comes out tomorrow," Haase said. "Please get started developing today."

The Android operating system got its start on smartphones and spread to tablets. Now Google wants to see it in cars, smartwatches, TV set-top boxes, and electronic eyewear. To help the OS span all those use cases, Google announced a new .

Google has succeeded in many ways with Android. It's the top smartphone OS, and Google expects it to displace Apple's iPad to lead in tablets, too. The company also is trying to bring it to good $100 phones for developing markets. But the mobile market is about as competitive as they come, and Google isn't satisfied. The upcoming L version of Android embodies the company's ambitions to make the software look better, work better, attract more developers, and attract more users.

Google's preview approach with the L version is a marked contrast with its past approach, where it wouldn't release new versions of Android until it was done. Beta tests and preview versions are a good way to please enthusiasts. But more important, they let programmers adjust to changes faster so their apps are ready for the new look and features as soon as possible. That means the overall Android ecosystem could move faster.

So what's in the L Preview? Haase and another Android team programmer, Dan Sandler, detailed many of the changes. Here's a look:

Overhauled notifications

Google and Apple have gradually realized the lock screen shouldn't be wasted on mobile phones, and the L release vastly expands its utility -- within privacy constraints set by app developers and users who might not want to show personal data that's not protected by an unlocking authentication process.

Screenshot from Stephen Shankland/CNET

"In L, you hear your phone buzz, you take it out out, turn it on, and that's it," Sandler said. "It's completely glanceable."

Notifications take the form of cards, as on the current KitKat, but use a black-on-white theme instead of the KitKat's dark look. The notifications can combine more graphical elements so users can more quickly understand things like the combination of who contacted them and what means they used. And the notifications use the depth information of the material design, with features like shadows cast on what's underlying on the screen.

Android L Preview also attempts to sort cards more intelligently, based in part on cues app developers can supply. Google introduced a new template to make it easier to build media-controller cards, the sort of thing that lets users fast-forward and pause video and audio.

The new notification system also is used in Android Wear for smartwatches.

Screenshot from Stephen Shankland/CNET

Animations and depth

The material design was inspired by the idea of a screen that had tactile features -- the kind of changing texture real-world objects have, as opposed to today's flat glassy screens. With the material design theme, developers can specify the "elevation" of an item -- how high it appears to be on the screen.

Also central to this more physically intuitive approach is animation. Buttons can ripple as they're pressed. Checkboxes can show a little splash of activity as they're tapped. And developers can specify a wide range of detailed animation behavior to control how elements bounce around, slide, expand, contract, appear, and disappear.

Better camera controls

Android L Preview lets programmers gather raw image-sensor data, which could potentially open the door to better image quality for photo enthusiasts. It also lets people capture uncompressed video data at 30 frames per second, hardware permitting, and control shutter speed, frame duration, and ISO sensitivity frame by frame.

New task switching

Android L adds finer controls to task switching. Instead of just letting people switch among apps, it'll show parts of apps -- individual documents or Web pages, for example -- so people can zero in on what they want sooner.

Cycling among those pages will use the depth and shadows of the material-design interface, too.

Screenshot from Stephen Shankland/CNET

Faster apps

The ART runtime -- software that actually runs the Android apps -- replaces Android's earlier Dalvik virtual machine. It means that, with no changes to software, apps will run twice as fast on Android L Preview.

New tools for Web-based apps

For those building apps using browser technologies, an approach that can ease development of apps that span multiple operating systems, Google is moving its WebView engine to the technology used in Chrome 36.

That means developers of third-party apps will get access to hardware-accelerated WebGL graphics, the WebAudio interface for better sound handling, and the WebRTC technology for real-time audio and video chats.

Better power efficiency

A tool called Project Volta will let programmers dig into application power usage with Android's debugging tools. And the Battery Historian will show how usage changes over time.

Power usage is a critical constraint on mobile devices. The Android L Preview also will debut a new power-saving mode for people who expect to be away from a charger for a long time -- something that handset designers already offer on their own with some Android phones.

Screenshot from Stephen Shankland/CNET

Smarter network handling

Android L will be able to detect some network problems before they get out of hand so apps can adjust accordingly.

"It allows a graceful handoff from one link to another -- if you're about to lose Wi-Fi when it's losing its range, you can rebuild [a video] stream on cellular [networks] with no interruption to the user," Sandler said.

Better Bluetooth

Android 4.3 introduced support for Bluetooth LE, a battery-preserving version of the short-range networking standard. That let phones connect to Bluetooth devices like heart-rate monitors to gather data.

Android L Preview goes another step with Bluetooth peripheral mode, which lets an Android device send Bluetooth to another device controlling the show.