The Linux kernel evolves constantly and
The current Linux stable release is Linux 4.3, from November 1st 2015.
Linux 4.4 is in development of course, this is an constant process.
Android phones and other embedded devices are usually not running the latest and greatest however.
Take for example Android device:
Which kernel is yours running?
Linux 3.0: 21 July 2011
Linux 3.4: 20 May 2012
Linux 3.10: 30 June 2013
Right here I have Nexus phones and tablets running all of these.
– Nexus S doesn't receive any update anymore since Android 4.1.2: Linux 3.0
– Nexus 5 and Nexus 7 2013, each running latest Marshmallow: Linux 3.4
– Nexus 9, latest Marshmallow: Linux 3.10
Even the newest one is 2.5 years old: how comes?
The article and its comments develop on that.
Discussion on Hacker News: https://news.ycombinator.com/item?id=10598441
Running a mainline kernel on a cellphone [LWN.net]
One of the biggest freedoms associated with free software is the ability to replace a program with an updated or modified version. Even so, of the many millions of people using Linux-powered phones, few are able to run a mainline kernel on those phones, even if they have the technical skills to …