The Samsung Galaxy S2 was announced in MWC 2011 and overall it was a worthy successor to the original Galaxy S. It was one of the thinnest devices back then, as it measured 8.49 mm. It was also one of the first phones with a dual-core processor and it performed quite well thanks to its 1 GB of RAM. Even if the 4.3-inch display didn't have the best resolution out there, it looked sharper than the one of its predecessor because of its AMOLED Plus technology. Other specs included an 8-megapixel camera on the back and a 2-megapixel camera at the front. The 16 GB of internal storage could be expanded with microSD cards and it launched running the latest version of Android at the time, Android 2.3 Gingerbread.
Android 6.0 has become available very recently to a few Samsung smartphones, but some more experienced users have been using custom ROMs based on Marshmallow to get some of the latest features. We've already seen the original Galaxy S unofficially running on the most recent version of Android called Marshmallow and now, it's the turn of the Galaxy S2 to run this version of the operating system. CyanogenMod, a very popular custom ROM for Android, is known for giving older devices the opportunity to try the new features brought by more recent versions of the OS. Now, CyanogenMod 13 nighties are available to download and install on the international version of the Galaxy S2 with model number i9100. 1 GB of RAM is one of the minimum system requirements for Android Marshmallow and since the dual-core processor on this handset is clocked at 1.2 GHz, the overall performance of the new operating system won't be as good as the one provided by new smartphones with more current components.
These files might also contain a few bugs and errors, which might also contribute for performance issues. Still, users get to experience a newer version that looks like stock Android and some additional customization options. If you know what you're doing, you can download the nighties from the link at the source and give Marshmallow a try in your Galaxy S2.