Key differences as cited by iFixit:
Apple's own A6 chip: Of course the key component is the Apple A6 processor. This is an unique Apple design with preliminary benchmarks showing roughly twice the performance of Apple's A5 chip. UMB TechInsights has looked inside the chip and Anandtech has followed up with its own analysis, showing a 3-core GPU (graphics processing unit), which is likely a PowerVR SGX 543MP3 running at 266MHz, according to the chip review site.
Easier to repair than 4S: The iPhone 5 could be the "most repairable iPhone we've seen in a while," according to the teardown notes.
4-inch display: The iPhone 5 is opened front-to-back so "replacing a cracked screen is going to be easier than ever...compare this to the iPhone 4s, where it took 38 steps to isolate the display assembly."
Unibody back: The unibody back resembles the older 3GS iPhone. "The case is reminiscent of the iPhone 3GS, while it maintains the square edges of the iPhone 4. We're having iPhone 3GS flashbacks with the easily accessible display assembly," said iFixit.
Home button redesign: The new home button assembly has an integrated metal support bracket, strengthening the switch and lessening the chance of wearing out the oft-used button.
Larger-capacity battery: The iPhone 5 battery has a higher voltage and slightly larger capacity than the iPhone 4S. The comparison breakdown is as follows: iPhone 5 battery:: 3.8V - 5.45Wh; iPhone 4S battery:: 3.7V - 5.3Wh; Samsung Galaxy S III Battery: 3.8V - 7.98Wh.
4G/LTE: The 4G LTE processor is a Qualcomm MDM9615M part.
Flash memory storage: Hynix is supplying the 16GB NAND Flash storage, possibly another sign of Samsung's shrinking status as a component supplier to Apple. That would confirm past speculation.
DRAM: 1GB Elpida LP DDR2 SDRAM system memory. Elpida, by the way, is the bankrupt Japanese memory chipmaker that U.S.-based Micron Technology is trying to acquire.
Sensors: STMicroelectronics L3G4200D (AGD5/2235/G8SBI ) low-power three-axis gyroscope. Same as iPhone 4S and iPad 2.
What is inside the iPhone 5? It's down here :
We needed a suction cup to get into an iPhone 5 because the iPhone 5 is opened front-to-back. Due to this replacing a cracked screen is going to be easier than ever.