playdelta
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Google Play Store now has Smart Delta App Updates [Download updated parts of apps only]

At Google I/O the company announced that the Google Play Store would be getting the ability to offer delta smart updates for apps, so that you wouldnt have to download an entire app again whenever it got an update.
This is a move that will save tons of people a lot of data, especially considering scenarios like how a game like Asphalt which weighs in over 1GB, can get an update with just two new cars, for which you will have to download the entire 1GB game update. Saving time and bandwidth, the Play Store will only download the actual changes of an app instead of the entire program or game. Very useful if you’re on a limited data plan.
Smart app updates is a new feature of Google Play that introduces a better way of delivering app updates to devices. When developers publish an update, Google Play now delivers only the bits that have changed to devices, rather than the entire APK. This makes the updates much lighter-weight in most cases, so they are faster to download, save the device’s battery, and conserve bandwidth usage on users’ mobile data plan. On average, a smart app update is about 1/3 the size of a full APK update.