The iPhone 4S is remarkably similar to the iPhone 4 on the outside, in fact, apart from a couple of notches on each side of the iPhone 4S, there's not much to differentiate between the two devices.
They both have the same volumetric dimensions (115.2mm x 58.6mm x 9.3 mm) but the iPhone 4S is a few grams (three to be precise) heavier than the iPhone 4 at 140g. We attribute that slight increase to a marginal increase in the weight of the battery.
The screen used (3.5-inch IPS TFT with a 960x640 pixel display), the glass cover at the back and the proprietary connector are all still there.
As for the confirmed differences; they are as follows: The SoC has been swapped from an A4 (Cortex A8 clocked at 1GHz) to an A5 (Cortex A9 dual core). Either 16GB, 32GB or 64GB onboard storage (the first iPhone with this capacity), Bluetooth 4.0 instead of Bluetooth 2.1, the rear camera goes from a five megapixel to an eight megapixel shooter, with full HD ready video recording and real time temporal noise reduction plus AirPlay Mirroring, Video mirroring and video out support.
The iPhone 4S also sees the introduction of CDMA 800/1900/2000 and 1xEV-DO, plus a better battery life compared to the iPhone 4 (Up to 8 hours on 3G vs Up to 7 hours on 3G).
As for the unknown. Apple hasn't confirmed how much onboard RAM the iPhone 4S has, what the clock speed of the A5 on the handset is (Apple doesn't list the A5 on its tech specs). We're not sure whether Apple has also upgraded its audio hardware or not - we would tend to think so given that Siri is only available on the iPhone 4S but not on the iPhone 4.
You can win an iPhone 4S by entering our competition - which ends on the 21st of October - here.