The size of update for Nexus 4 and Nexus 7 2012 Wi-Fi is 174.5MB and 101.6MB respectively. As of now, there is no official change log has been released by Google, while it is outlined as improves performance and stability and fixes bugs.
Users can see the update in the system notification, otherwise users can manually check by going into Settings > About Phone > System Updates.
Android 5.1 is the first big maintenance release for Lollipop, fixing bugs and improving performance and stability over the original 5.0 release.
Moving on to the features of Android 5.1, the quick settings panel has been polished up a bit in Android 5.1. Also, Android 5.1 also introduces dual SIM support as a built-in Android feature.
Android 5.1 brings some much-needed clarity to Lollipop's somewhat confusing screen pinning feature, which was designed to make it easier to lock kids or guest users into a particular app.
Device Protection in Android 5.1 will help to secure your device even if it's lost or stolen. With this feature enabled, a thief won't be able to use your device, even after factory resetting it without having your Google account login details.
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In this update, Google has made some tweaks to the volume slider and interruptions system. Previously, in the Android, there is no traditional option for Mute.
Now in this update, None," "Priority," and "All" are now accompanied by their corresponding icons, which should make it easier for new users to relate these to their status bar icons.
And when enabling "None" or "Priority" mode for a specific time period, you'll see the exact time it'll be enabled for.
If you use Android's "Downtime" feature to control notifications after some time, you will be able to choose the kinds of interruptions allowed, which is "Priority" or "None." Previously this feature defaulted to "Priority" mode, with no way to change this.
And some other small features includes New animations in Clock app, Contacts lose colored overlay and Google+ linkage, Sticky soft keys fix, Hide 'Heads-up' notifications without dismissing, A new status bar icon when there's no SIM inserted, NuPlayer now the default streaming player.