Running a newly released version of Windows or Mac OS X on a 3-year-old personal computer is an unremarkable feat.
But it's a lot more difficult in the smartphone world, where hardware and software have been changing at a breakneck pace. That's why I recommend watching this brief demonstration of Ice Cream Sandwich, aka Android 4.0, on the first-generation Android phone, the T-Mobile G1 from October 2008.
XDA Developers forum member jcarrz1 posted the video and an alpha version of his OS build yesterday, nine days after Google released the Ice Cream Sandwich source code.
As you may expect, the new OS drags on the comparatively ancient hardware, with slow app launches and long lags between a touch action and the phone's response. But all the ICS apps work.
What doesn't work at this stage, jcarrz1 said: Wi-Fi networking, Bluetooth, and screen rotation.
Ice Cream Sandwich arrived a week ago on the Samsung Galaxy Nexus, a much more powerful device. It's not clear yet which beyond a handful of phones will get the ICS upgrade, but jcarrz1's work shows that business reasons, not technology reasons, are most likely responsible for keeping it off newer phones.
The current version of Apple's mobile operating system, iOS 5, requires a 2009-era iPhone 3GS or newer phone. In the Android realm, it's less common to see the latest OS supported on older phones.
In the ICS on G1 demo, jcarrz1 shows the unlock screen, the settings app, the phone app, and the clock. I'm guessing we won't be seeing Riptide GP anytime soon, though.