Ice Cream Sandwich and TouchWiz

The Galaxy S3 is running on Android, Google's mobile operating system. Specifically, it's powered by Android 4.0, aka Ice Cream Sandwich (ICS). Until very recently ICS was the latest version of Android but that honour now goes to 4.1 Jelly Bean.

The S3's home screens will be familiar to most Android users -- with a launcher bar of apps and space above to fill with widgets and more apps.

Samsung has not yet confirmed whether the S3 will get an update to Jelly Bean. If you're desperate to get your hands on the latest Google OS, you might be better off opting for the Samsung Galaxy Nexus, which is due to get Jelly Bean later this month.
Despite Samsung's reticence to confirm a Jelly Bean update for the S3, it seems pretty likely it will get one. Do be prepared for a bit of a wait though -- the S2 ICS update was a long time coming.
Android is a powerful, flexible operating system that affords users loads of scope to customise and tinker with their phone. But the wealth of options and tools available can be overwhelming to newcomers, which makes having a really slick interface especially important.
Atop ICS, Samsung has plastered its own software, called TouchWiz. It's the same colourful interface you'll see on kit like the Galaxy S2 and Galaxy Note.
TouchWiz on the S3 looks polished, with lots of carefully drawn icons and easy-to-read fonts. But when it comes to ease of use, it's not always as well thought through as rival mobile maker HTC's Sense 4.0 Android overlay. At times, as you poke and prode TouchWiz, the intuitive action does not yield the hoped-for result.

On the left are the Recent Apps thumbnails that ICS serves up; on the right is the S3's notifications tray, fit to burst.

For example, adding widgets to the home screens is not done by long-pressing the place where you want to add the widget. Rather, you have to dive into the apps view, switch to the widgets tab and long press on a widget -- then move it onto the home screen position of your choice.
It's an inelegant way of doing things and, while it's only a minor quibble, it is indicative of TouchWiz's tendency to be a tad gnomic.
Another example is TouchWiz's notifications interface. Even if you turn on SMS notifications in the settings, if the notifications icon is toggled off in the notifications tray, you won't hear any sounds until it's toggled on. That's fine once you know about the existence of this icon. But if you haven't found it yet, you'll be really confused about why you can't hear any SMSes coming in.
S2 owners won't have any trouble navigating the S3's interface since they're retreading familiar ground. But newbies will certainly need to get accustomed to Samsung's way of doing things.