Follow this link for our extensive coverage of Apple iOS 5 - the new operating system for all current iPhone models.
It's been 16 months since the iPhone 4 was launched. That's plenty of time for rivals to catch up and - in the case of certain models such as the Samsung Galaxy S2 - overtake Apple's flagship smartphone in certain areas.
Now Apple has responded with the iPhone 4S, a handset that looks the same as the old one, but with more powerful internals. It's no surprise that the company has updated the iPhone 4 rather than launch an all-new 'iPhone 5' - this simply follows the pattern that started with the iPhone 3G and 3GS. Outwardly, the iPhone 4S is exactly the same as its predecessor, save for breaks in the external antenna in different places. The newcomer has the same screen, buttons and edge-to-edge glass front and rear; most cases made for the iPhone 4 will fit the 4S with no issues, but the mute switch has moved slightly so those with small apertures for the switch may not fit properly.
So what's new? The main upgrade is the A5 processor - the same as used in the iPad 2. This dual-core chip is estimated to run at 800MHz - Apple doesn't disclose the precise details of its processors. It's around 25 per cent slower than the iPad's chip, and considerably slower than the Galaxy S2's 1.2GHz processor. Apple claims the iPhone 4S is twice as fast as the 4, and up to seven times as fast for graphics (versus the iPad's 'nine times faster' claim).