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.

Source: iFixit

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  • eliotw - Thursday, October 13, 2011 - link

    Anand - I enjoy your site and it's disappointing to see you continuing to support this misinformation:

    "lack of true multitasking on iOS"

    iOS implements "true" preemptive multitasking but it is tightly controlled for arguably good reasons. It isn't a cooperative "task switcher" like MacOS 7.

    I expected Anandtech would be a bit more technical and a bit more accurate than this.

  • Anand Lal Shimpi - Thursday, October 13, 2011 - link

    The argument isn't that it's not preemptive, but rather most of what you're not using is kept out of memory (as you pointed out, for good reasons). The point is simply that a doubling of DRAM size won't necessarily improve performance in existing workloads as a result since memory management is pretty strict already.

    Take care,
  • Anand Lal Shimpi - Thursday, October 13, 2011 - link

    Clarified a bit, hopefully that makes it better :)

    Take care,
  • eliotw - Thursday, October 13, 2011 - link

    Thanks I think that's much better.
  • Wolfpup - Friday, October 14, 2011 - link

    It doesn't have true multitasking. Yes, the underlying OS does, but it's not actually exposed to the users or third parties, so practically speaking it does not.
  • Wolfpup - Friday, October 14, 2011 - link

    For that matter, PalmOS 5 a decade ago actually had real multitasking. It was cooperative, but did work, and was available to any developer.
  • headbox - Sunday, October 16, 2011 - link

    Yeah, and when you use an iPhone you're always thinking "oh damn, I wish this was as awesome as PalmOS 5" :rolleyes
  • ImSpartacus - Thursday, October 13, 2011 - link

    Is "28/38nm A6" a typo?

    I've heard of both 32nm processes and 28nm processes, but not anything at 38nm. Really, I'm just comparing it to "28/32nm A5" earlier in the sentence. I don't have the technical knowledge to say that it is incorrect.
  • Anand Lal Shimpi - Thursday, October 13, 2011 - link

    Fixed :)
  • madoublet - Thursday, October 13, 2011 - link

    From what I understand, Apple maintaining 512MB of RAM has much to do with battery life. An increase in RAM would likely draw more power. Wouldn't you agree?

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