Google Nexus S is a smartphone released in 2010 and produced by Samsung. It has been inspired by the Galaxy S, which has been one of Samsung's most popular smartphones. Though Google didn't release an Android 4.2 Jelly Bean update for it, unfortunately.
Fortunately the Android 4.2 Jelly Bean has been ported to the Nexus S device, thanks an Android developer called knzo. The ROM isn't yet 100% stable, though it's fully functional and you can give it a try.
Android 4.2 has been recently released and Google announced that the Nexus S in't going to get anything newer than 4.1.2 Jelly Bean, which is a same, considering that 4.2 doesn't have higher hardware requirements. This means it should run as smooth as 4.1.
The Google Nexus S features a 1Ghz Cortex A8 processor, 4-inch 800x480 Super AMOLED display, 16GB of internal storage, 512MB of RAM, a 5MP primary camera and a VGA frontal camera. These specs should definitely be enough for Android 4.2 to run smoothly, so be positive, because you will get it in the near future. Maybe even faster than other newer smartphones, which make it harder due to lack of source codes, carriers and phone makers.
Hopefully knzo will be able to turn it into a stable ROM and fix the bugs, so all Nexus S owners can use it without any problem. We will let you know once this happens, so you can safely upgrade to it.
We are now trying it on our own Google Nexus S and we will let you know how it works, along with a guide to help you install it.
Update: knzo has pulled the download link and he will re-release the ROM once it becomes more stable. We will keep you updated.