The venerable Samsung Galaxy Nexus is the device that introduced the world to Android 4.0 Ice Cream Sandwich, which at the time was a significant departure from Android 2.3 Gingerbread, as used on smartphones, and Android 3.2 Honeycomb, which was used on Android tablets. There were several ideas behind Android 4.0 Ice Cream Sandwich, including that the new software would be very similar on both smartphones and tablets (and why the particular name was chosen as it reflected two device types with the one software). The Galaxy Nexus was the first Nexus smartphone with a 720p AMOLED HD screen and a dual core processor, but rather than use a Qualcomm (or Samsung) chipset, Google used a Texas Instruments OMAP 4460 processor, a dual core System-on-Chip clocked at 1.2 GHz. The Galaxy Nexus also came with 1 GB of RAM and either 16 GB or 32 GB of onboard memory. Samsung provided a replaceable 1,750 mAh battery in the GSM version but no MicroSD card slot.
Google's decision to use the Texas Instruments OMAP resulted in much speculation as to why Google picked this particular chipset. At the time, the OMAP 4460 was not a new processor and used a relatively older GPU (the PowerVR SGX540) but it included a HD video hardware accelerator and a dual-channel memory controller, which for the new version of Android with improved multitasking performance was seen as important. Unfortunately, Texas Instruments were to close down their mobile chipset business in late 2012 and this meant that there would be no more official development of the platform. No newer versions of the OMAP chipset is not a problem but closing the doors on the software engineers meant that there would be no more updates to the hardware drivers. This is the code that sits between the hardware and the operating system and as Google releases new versions of Android, the drivers also need updating to maintain compatibility and work with new software features. This is one of the reasons why Google did not progress the Galaxy Nexus software beyond 4.3 Jelly Bean.
However, this is Android, where just because the manufacture does not wish to pursue newer software versions, this does not stop people! The Galaxy scene, and in particular the Nexus devices, have seen a healthy cottage industry arise to bring newer versions of Android software to older devices no longer officially supported. We've seen Android 4.4, 5.0 and 5.1 released for the device plus new hardware drivers written to improve performance and stability. And now a developer by the name of Ziyan on XDA Forums has released an experimental Android 6.0 Marshmallow ROM for the Samsung Galaxy Nexus. Ziyan cautions that the software is not ready as a daily driver and has two known major bugs - video recording crashes and NFC simply doesn't work. However, there are other bugs and performance hiccups, including an issue with how the Galaxy Nexus works with memory. Android 6.0 Marshmallow as a 1 GB limit but the standard kernel gives the Galaxy Nexus around 750 MB of free memory, so performance is substandard. There are a number of workarounds being discussed in the XDA Forums at this time and of course, this is an experimental build - but if you own a Samsung Galaxy Nexus and if you are wanting Android Marshmallow, hit up the source for this article for links to the download and instructions.