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If you're a Samsung Galaxy S6 or S6 Edge owner disgruntled that your expensive phone's software is a generation behind rivals, you'll be glad to hear the latest version of Google's Android is arriving.

Samsung said Monday it will update the two top-end phones to Android 6.0 Marshmallow software starting immediately and update some other Galaxy devices gradually as well. Exactly when you receive the update will depend on where you live and what carrier you subscribe to. Samsung did not say whether the supersized S6 Edge+ would also receive the update.

A major software upgrade such as this can make a stale smartphone feel shiny and new again, at least on the inside. Marshmallow brings a host of new features, including a redesigned app drawer, better battery life and more sophisticated Google Now integration to Android. The Marshmallow update, which Google announced in May 2015 and released in October with its own Nexus phones, is the biggest change to the software since October 2014.

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Android is the most widely used phone software, but for many customers, the version that comes with their phone is the only one they'll see. That means they won't see new features until they buy a new phone and that developers don't have as much incentive to rapidly retool their apps to take advantage of new features. As of the beginning of this month, Marshmallow was on less than 1.2 percent of all Android devices.

Samsung also is updating its Edge screen feature alongside Marshmallow, expanding the width of a panel running down the one edge of the phone that customers can use to reach contacts, launch tools and apps, and browse news, company stocks and sports scores.

Google itself released the first Marshmallow-powered phones with the Nexus devices the company develops in partnership with major manufacturers. Next came LG's own flagship phone, the G4. Now Samsung has caught up, squeezing in a whole day ahead of rival HTC, which is starting to upgrade the One M9 to Marshmallow starting Tuesday, according to Mo Versi, the company's VP of product management.

Unlike Apple, which makes every iPhone and the iOS software they run, Android phone makers need to go through a cumbersome process to update customers' phones. They must first wait for Google to finish tinkering with the software before they can begin to add their own flourishes and ensure compatibility with their own devices.

Marshmallow will give restore some of the cachet of the Samsung Galaxy S6 and S6 Edge, the two top-end phones from the biggest Android phone maker. But their position at the top of Samsung's product line won't last much longer. They are likely to be superseded as soon as next Sunday, when Samsung is expected to unveil its two new flagships, the Galaxy S7 and S7 Edge, at an event during the Mobile World Congress tech show in Barcelona.

CNET will be out in Barcelona covering Samsung's event, bringing you news, analysis and hands-on photos and video from the show floor. In the meantime, check out the latest news regarding when you can expect your Android phone to get Marshmallow.