Preceded by the tasty-sounding Android OS versions 1.5 (Cupcake), 1.6 (Donut), 2.1 (Éclair) and 2.2 (Froyo), 2.3 (Gingerbread), version 4.0, codenamed Ice Cream Sandwich (ICS), is by far the most important update to Google's mobile operating systems.

Initially available on the Galaxy Nexus (read the Hands on Review here), ICS has started rolling out for users of the previous "Pure Android" device, Samsung's Nexus S, through an over-the-air update.

Like many impatient Nexus S users, I opted to download and install the ICS 4.0.3 version update myself following instructions I found online, and have been testing the software for the past few days.

The Unifying OS

What makes Ice Cream Sandwich so significant is that it is designed to unify Google's tablet and smartphone operating systems. This means developers will have an easier time writing applications; and users can expect very similar experiences between tablets and smartphones running ICS.

This is the biggest change to the Android OS since it first came out and Google has gone to great lengths to improve the look and feel and make things more intuitive for users. Google hopes ICS will be the answer to the valid criticisms about the fragmentation of Android.

You can see the evolution of the Android OS in the photo at the top of this story. The left screen shows Google Android OS 1.6 "Donut" as it first appeared in the T-Mobile G1; and the right shows version 4.0.3 "Ice Cream Sandwich" running on a Samsung Nexus S.

What's New

ICS brings the ability to create folders for apps, in a very similar way iOS. Simply drag one app icon onto another and they make a folder. You can see the folder structure in the screen shot on the right. Eventually, most of the app logos are stacked one on top of each other in a singular icon, tapping on this bring up another window where all the apps in the folder are easily accessible.

ICS allows users to take screenshots at any time by pressing the volume-down and power buttons simultaneously for a few seconds. This will grab the screen and place it under a Screenshots folder. This is a great feature for app reviewers and developers who need to take visuals to accompany their documentation.

New folders allow similar apps to be collected while Google Plus is heavily integrated across the system. The new camera application gives users improved control over white balance, scene selection, flash and even offers handy photo editing tools.

Fans of the Android browser will be happy to learn that it now sports tabs. Web pages can be saved offline for later viewing, and users can directly request the desktop version of a site. Browser performance was demonstrably better than the previous version and felt a little faster.

Notifications are easier to manage and can now be dismissed with a quick swipe of the finger, à la webOS.

The Calendar and the Gmail apps have also received overhauls that improve their design and function. The Calendar app is easier to manipulate, and now allows for easier zooming into specific cells, making it faster to add events and dates.

The camera also receives a bunch of updates, including on-screen controls for scene modes, exposure, white balance and flash, as well as shooting modes. As discussed in the Galaxy Nexus Hands On, ICS also debuts a neat panorama feature along with video and still photo capabilities. Built-in face detection and photo retouching are welcome additions to the photo app.

Control over currently running apps has also been improved, as has the ability to track of which applications are using up processor bandwidth. This helps users understand what apps are using up data or slowing the system down.

The updated design of Ice Cream Sandwich is cleaner and looks more professional. The Web browsing experience adds tabs and even the Android Marketplace gets a makeover.

Coming soon to Ice Cream Sandwich is the much-awaited Google Wallet, This complement of mobile payment solutions exploits the Nexus phones' NFC (Near Field Communication) capabilities, allowing transactions to be triggered by the smartphones.

Battery Life Remains Poor

I was pleased with the improvements that Ice Cream Sandwich brought to my older Android phone. Everything feels better integrated and more fluid. Being able to download the latest version of the Android OS shortly after it has been released is the biggest advantage of having a "pure Google" Nexus device.

While ICS has tightened up the interface and improved the user experience, it doesn't seem to have improved the poor battery life of the Nexus S.

This has been a constant issue with Android phones in general, and possibly a result of various apps running in the background accessing updates or the phone's location services using the GPS and/or radios.

While battery life on ICS is slightly better than on Gingerbread, we still it hard to get through a full day of use without charging.

Note that not all the apps are currently optimized to run on Ice Cream Sandwich and there are likely to be a number of updates to make the experience and overall of Android's OS performance much better on the older hardware.