Google I/O is nearly upon us, and, as usual, we're expecting a lot of big announcements from the company's opening-day keynote on Wednesday. We've already taken a broad look at all the stuff that Google is known (or thought) to be working on, but, to provide some context for those upcoming announcements, we thought it would be instructive to look at some of the company's past announcements, too.

The whole Android update situation

Putting Android app updates in the Google Play store means that more users get more features more quickly, but it also makes Android that much less "open."

Let's start with Android updates. Current rumors say we won't be getting another new Android version before Q4 of this year, but, as we've seen, Google has been working to blur the lines between new OS versions by releasing individual apps into the Google Play Store. You'd expect things like Chrome and Gmail to be available as separate apps, but in the last year Google has put everything from its keyboard to the camera app to its application launcher in Google Play as well. The most recent case was the standard e-mail app added just last week.

We've written about this phenomenon several times, and it has both good and bad effects on the ecosystem. On one hand, it frees Google to deliver new features even to users whose devices are several Android versions behind. On the other, those Google Play store apps are closed-source, and Google generally stops making big new additions to the open-source AOSP versions of those apps after replacing them.

Android on your wrist

All of that said, Google does still use full Android updates to introduce UI design changes, new APIs, and support for new low-level technologies. Look at Android 4.3 as the archetypal modern Android update. It made very few obvious, user-facing changes over Android 4.2, in part because most user-facing features were being delivered via Google Play. But it introduced lots of smaller, less-obvious changes that are going to be important for the platform going forward—a new version of the OpenGL ES API, improved SELinux support, and TRIM support for SSDs were all part of Android 4.3. Version 4.4 made just as many "invisible" changes, introducing a new optional runtime called ART , security improvements to the way the OS handles SD cards, and better support for devices with 512MB of RAM. Current rumors say we won't get a new version of Android before Q4 of this year—if a new version isn't announced at the show, it doesn't mean Google's not working on one.

Two additions in Android 4.3—native support for Bluetooth Low Energy and the Notification Access API—set the stage for a bigger extension to the platform. Android Wear , Google's upcoming smartwatch platform, uses both of those features to get its job done. Developers who have integrated support for the new notifications into their apps will already have functional Android Wear "apps" up and running on day one.

Google and its OEMs have had the benefit of watching several other manufacturers put out smartwatches, from the modestly successful Pebble to the functionally dubious Samsung Gear line to the curiosity that is Qualcomm's Toq. Expect the first Android Wear hardware makers—Motorola, LG, and possibly even Samsung itself—to have learned valuable lessons from those early efforts.

Chrome and Chrome OS, and platforms within platforms

Chrome OS and Chromebooks don't make as much noise in the tech world as Android, but inexpensive Chrome hardware keeps getting better , and Google is slowly getting that hardware into more hands. Google can provide e-mail and other services along with pretty robust computer management without requiring customers to have any on-site servers or infrastructure, which makes the computers particularly appealing to schools trying to provide laptops to students

Also worth noting: while Android is Google's big software platform, Chrome is still Google's best platform-within-a-platform, a way for the company to rope people into its ecosystem even if they don't use Google hardware or operating systems. Google Now got its start on Android, but Chrome brought it to Windows and OS X. Chrome run in full-screen mode on a Windows 8 PC basically looks and works like Chrome OS. Chrome Remote Desktop allows different computers and even phones to share screens. Any Chrome announcements made at the show this year should benefit anyone, not just people carrying Android phones or Chromebooks around.

Services tie it all together

If you remember our Google I/O coverage from last year, you might recall that we went into the show expecting news about a new Android version (and perhaps some new hardware) and walked out with a whole pile of updates to Google's various services. Announcements like the move from Google Talk to Hangouts , updates to Google Maps and Search , and the addition of Google Play Music All Access were small individually, but in aggregate they add up to a pretty substantial update to the Google platform.

Read those pieces, and you'll get a preview of what Google could announce at I/O this year: service updates that you'll be affected by whether your technological world revolves around Google entirely, or you just pop over to google.com in Internet Explorer every once in a while to run a search. That's one of the big differences between Apple and Google in 2014. Apple's WWDC was mostly about making Apple devices work better and more seamlessly with one another. Google is all about drawing you into its ecosystem regardless of what device you're using.

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