Stefan Mileschin

The folks over at iFixit are hard at work dissecting the newly announced/soon-to-be-available iPhone 4S. We've already gone over performance expectations as well as provided a high level hardware analysis, but with a tour inside the smartphone we're able to confirm a few suspicions. First is the Qualcomm MDM6610 baseband, a slightly different part from the MDM6600 that we had theorized earlier. There isn't a whole lot of documentation out on the 6610 but we're digging.

The second confirmation iFixit's teardown gives us is the size of the A5's on-package memory: 512MB. A quick look at the image above yields the Samsung part number: K3PE4E400B-XGC1. Each highlighted E4 refers to a separate 2Gb LPDDR2 die. The A5 features a dual-channel LPDDR2 memory interface, thus requiring two 32-bit die to fully populate both channels. The final two characters in the part number (C1) refer to the DRAM's clock period, in this case 2.5ns which indicates a 400MHz clock frequency (F=1/T). My assumption here is Samsung's part number is actually referring to clock frequency and not data rate, implying there are a pair of LPDDR2-800 die in the PoP stack. It's not entirely uncommon to run memory at speeds lower than they are rated for, a practice we've seen in graphics memory in particular for as long as I can remember, so I wouldn't take this as proof that Apple is running at full LPDDR2-800 speeds.

At a high level there aren't any surprises here, the A5 on the iPhone 4S is virtually identical to what was used in the iPad 2 - although running at a lower clock speed and likely a lower voltage as well. Many are surprised by the inclusion of only 512MB of RAM on the A5's PoP stack, however since most apps not in use are kept out of memory to begin with having more memory doesn't actually buy you a whole lot of performance. There are also potential battery life concerns with larger DRAMs: more room for apps to remain resident in memory leaves more DRAM cells to refresh, which impacts power consumption (although eventually Apple will have to cross this bridge, likely with the next process node transistion). I suspect the biggest issue created by not outfitting the iPhone 4S with more DRAM is limiting game developers to smaller levels, fewer unique textures, etc...

My real question is what comes next. Will we see a 28/32nm A5 used in the iPad 3 in 1H 2012 or will Apple continue to push the envelope and embrace a 28/32nm A6 with a pair of Cortex A15s in the second half? The latter is what I'd like to see, although it would effectively move all of the flagship iOS product launches to a fall ordeal.

http://www.anandtech.com/show/4964/i...lpddr2-mdm6600