The Apple iPad Review (2012)
by Vivek Gowri & Anand Lal Shimpi on March 28, 2012 3:14 PM ESTA Word on Packaging
Unlike the first two iPads, the 3rd generation iPad abandons the high density flip-chip PoP SoC/DRAM stack and uses a discrete, flip-chip BGA package for the SoC and two discrete BGA packages for the DRAMs.
If you think of SoC silicon as a stack, the lowest layer is where you'll find the actual transistor logic, while the layers of metal above it connect everything together. In the old days, the silicon stack would sit just as I've described it—logic at the bottom, metal layers on top. Pads around the perimeter of the top of the silicon would connect to very thin wires, that would then route to the package substrate and eventually out to balls or pins on the underside of the package. These wire bonded packages, as they were called, had lower limits of how many pins you could have connecting to your chip.
There are also cooling concerns. In a traditional wire bonded package, your cooling solution ultimately rests on a piece of your packaging substrate. The actual silicon itself isn't exposed.
As its name implies, a flip-chip package is literally the inverse of this. Instead of the metal layers being at the top of the stack, before packaging the silicon is inverted and the metal layers are at the bottom of the stack. Solder bumps at the top of the silicon stack (now flipped and at the bottom) connect the topmost metal layer to the package itself. Since we're dealing with solder bumps on the silicon itself rather than wires routed to the edge of the silicon, there's much more surface area for signals to get in/out of the silicon.
Since the chip is flipped, the active logic is now exposed in a flip-chip package and the hottest part of the silicon can be directly attached to a cooling solution.
An example of a PoP stack
To save on PCB real estate however, many SoC vendors would take a flip-chip SoC and stack DRAM on top of it in a package-on-package (PoP) configuration. Ultimately this re-introduces many of the problems from older packaging techniques—mainly it becomes difficult to have super wide memory interfaces as your ball-out for the PoP stack is limited to the area around your die, and cooling is a concern once more. For low power, low bandwidth mobile SoCs this hasn't really been a problem, which is why we see PoP stacks deployed all over the place.
Take a look at the A5, a traditional FC-BGA SoC with PoP DRAM vs. the A5X (this isn't to scale):
Images courtesy iFixit
The A5X in this case is a FC-BGA SoC but without any DRAM stacked on top of it. The A5X is instead covered in a thermally conductive paste and then with a metallic heatspreader to conduct heat away from the SoC and protect the silicon.
Given the size and complexity of the A5X SoC, it's no surprise that Apple didn't want to insulate the silicon with a stack of DRAM on top of it. In typical package-on-package stacks, you'd see solder bumps around the silicon, on the package itself, that a separate DRAM package would adhere to. Instead of building up a PoP stack here, Apple simply located its two 64-bit DRAM devices on the opposite side of the iPad's logic board and routed the four 32-bit LP-DDR2 memory channels through the PCB layers.
iPad (3rd gen) logic board back (top) and front (bottom), courtesy iFixit
If I'm seeing this correctly, it looks like the DRAM devices are shifted lower than the center point of the A5X. Routing high speed parallel interfaces isn't easy and getting the DRAM as close to the memory controller as possible makes a lot of sense. For years motherboard manufacturers and chipset vendors alike complained about the difficulties of routing a high-speed, 128-bit parallel DRAM interface on a (huge, by comparison) ATX motherboard. What Apple and its partners have achieved here is impressive when you consider that this type of interface only made it to PCs within the past decade.
Looking Forward: 12.8GB/s, the Magical Number
The DRAM speeds in the new iPad haven't changed. The -8D in the Elpida DRAM string tells us this memory is rated at the same 800MHz datarate as what's used in the iPhone 4S and iPad 2. With twice the number of channels to transfer data over however, the total available bandwidth (at least to the GPU) doubles. I brought back the graph I made for our iPhone 4S review to show just how things have improved:
The A5X's memory interface is capable of sending/receiving data at up to 12.8GB/s. While this is still no where near the 100GB/s+ we need for desktop quality graphics at Retina Display resolutions, it's absolutely insane for a mobile SoC. Bandwidth utilization is another story entirely—we have no idea how good Apple's memory controller is (it is designed in-house), but there's 4x the theoretical bandwidth available to the A5X as there is to NVIDIA's Tegra 3.
There's a ton of memory bandwidth here, but Apple got to this point by building a huge, very power hungry SoC. Too power hungry for use in a smartphone. As I mentioned at the start of this article, the SoC alone in the new iPad can consume more power than the entire iPhone 4S (e.g. A5X running Infinity Blade 2 vs. iPhone 4S loading a web page):
| Power Consumption Comparison | ||||
| Apple A5X (SoC + mem interface) | Apple iPhone 4S (entire device) | |||
| Estimated Power Consumption | 2.6W—Infinity Blade 2 | 1.6W—Web Page Loading | ||
There's no question that we need this much (and more) memory bandwidth, but the A5X's route to delivering it is too costly from a standpoint of power. There is a solution to this problem however: Wide IO DRAM.
Instead of using wires to connect DRAM to solder balls on a package that's then stacked on top of your SoC package, Wide IO DRAM uses through-silicon-vias (TSVs) to connect a DRAM die directly to the SoC die. It's an even more costly packaging technique, but the benefits are huge.
Just as we saw in our discussion of flip-chip vs. wire bonded packages, conventional PoP solutions have limits to how many IO pins you can have in the stack. If you can use the entire silicon surface for direct IO however, you can build some very wide interfaces. It also turns out that these through silicon interfaces are extremely power efficient.
The first Wide IO DRAM spec calls for a 512-bit, 200MHz SDR (single data rate) interface delivering an aggregate of 12.8GB/s of bandwidth. The bandwidth comes at much lower power consumption, while delivering all of the integration benefits of a traditional PoP stack. There are still cooling concerns, but for lower wattage chips they are less worrisome.
Intel originally predicted that by 2015 we'd see 3D die stacking using through-silicon-vias. Qualcomm's roadmaps project usage of TSVs by 2015 as well. The iPhone won't need this much bandwidth in its next generation thanks to a lower resolution display, but when the time comes, there will be a much lower power solution available thanks to Wide IO DRAM.
Oh and 2015 appears to be a very conservative estimate. I'm expecting to see the first Wide IO memory controllers implemented long before then...
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Anand Lal Shimpi - Thursday, March 29, 2012 - link
Max brightness.Take care,
Anand
h4stur - Thursday, March 29, 2012 - link
I use it every day. But it don't see enough improvement in the new version, to warrant an upgrade. I view the high ress as an actual downgrade. As the machine will have to upscale the majority of the content.mavere - Thursday, March 29, 2012 - link
text text text text.If that means nothing to you, then the upgrade won't do anything for you. For the rest of us, this screen is a godsend.
darkcrayon - Thursday, March 29, 2012 - link
I'm guessing the machine will have to upscale very little content other than images on the web in a month or two. Every major app will be updated for the higher resolution, no new app will be caught dead not supporting the new resolution, and text based apps get a "free" upgrade to the higher resolution. If your primary concern is whether images on the web will be updated, then that's an area for disappointment. Otherwise...adityarjun - Thursday, March 29, 2012 - link
I love this site and most of the reviews. Since the ipad has been released I have been coming here 6-7 times a day just for this review. Glad to see it finally put up. I just registered here specifically to ask a few questions.While I was more than impressed with the review, I was hoping to read something about the use of Ipad as an educational tool. This section was sadly missing.
I am a engg grad student and I am currently looking for a good pdf reader. The only viable options for me are the new Ipad or the Kindle DX (the kindle 6" is too small). While the Kindle does sound good , the problem is that some of my pdf books are over 100mb and full of mechanical drawings. Will the Kindle be able to handle that, especially if i want to frequently jump pages or refer to multiple books side by side? I have never seen a Kindle in person so anyone who has used it, please comment.
Reading ebooks on my laptop is a pain. I often read through the night and that is not possible for me to do on a laptop. The vertical height is too small and I often end up turning the laptop 90 degree to read. Not to mention, carrying around a laptop in your hand is impossible for long durations. Plus the zoom options on Adobe reader are just weird. In short, I am really uncomfortable reading on a laptop. I have tried both a 14" 1366*768 screen as well as 17" 1920*1080 screen
On the other hand, ipad gives me the advantage of iOS. I will also be able to see OCW videos on the ipad as well as watch my college slides (ppt). Ipad owners please comment-- can i play .avi or real media player file on it directly or through an app? I can also use the educational apps like Khan academy plus it can serve as a note taking device. The disadvantage of the ipad is that reading on it through the night will probably leave me blind in a year or so. I have myopia and my power is -8D. That is one BIG disadvantage, or so I have read. I have never used an ipad so perhaps someone who uses it can share their experience of reading on it for hours at a stretch.
I am really confused about this so I hope the collective intelligence of this site will help me make an informed decision. And I would really like to see a page in the reviews of tablets that talk about the reading and note talking abilities and the educational purposes they can serve.
Monobazus - Thursday, March 29, 2012 - link
I understand your desilusion with the ommission here of any specific discussion of the advantages or desadvantages of using the iPad as a book reader. After all, that may probably be one of the main usages of the iPad, apart from browsing the web or checking the email or Facebook posts. But anandtech.com is mainly a tech site for geeks and technically oriented people, and we must understand that putting a special emphasis on specs and speeds is more interesting for the majority of its readers. For an analysis of your question, you could perhaps go into one of the various sites that deal with ebook readers. Unfortunately most of them, as far as I can tell, have not the level of expertise or care that anantech.com has in its analysis (see http://www.the-ebook-reader.com/ipad-3.html as an example).Now to your questions. I have no direct experience with the new iPad or the kindle DX. I have an iPad 1 and a kindle 3 (the one with the 6" screen and no touch controls). I haven't seen yet the new retina display of the iPad, but from what I've been reading it's much better on text than the previous editions. I doubt however that it is as good for the eyes as the eInk screens are - these are reflective and, as such, closer to paper than LCD screens. From my experience - I'm an intensive reader and use glasses, due to my advanced age - eInk screens don't put as much stress on the eyes as the emissive screens do. If you are planning to read through the night with a LCD screen use an indirect ambient light and plan for frequent periods of rest.
On the other hand, handling pdfs on the Kindle is an awful experience. A DX is certainly better than a 6" one, no doubt, because the bigger screen allows for larger type. On a 6" screen you can forget pdfs. You can't read them. If your typical pdfs can be accommodated in a 9,7" screen without zooming, then a DX can be the eReader for you. But be careful with the illustrations: I think the DX has the same controls that the 6" non-touch kindle. If that's the case be prepared for a bad experience with the illustrations, specially if they are detailed and need zooming (or if they have colour). The DX is a non-touch machine. The iPad touch controls are much better.
You can't see two documents side by side on any of these readers: not on the iPad and not on the Kindle. For that you need a laptop. On the iPad you can use a trick: open one document in one app (say, on the eBook app) and the other in other app (say, on the kindle reader). By switching rapidly between them, you can see the two documents in rapid succession. You can't do that on the Kindle. But this is a trick, a compromise, and not the same thing as looking to two documents side by side.
As to seeing ppt's and videos, the iPad is the way to go. There are apps for that. The kindle has not that capability.
In the end, my advice is this: try to get access to an iPad before buying, and see if it meets your expectations for reading clarity and comfort. Getting access to a DX before buying may be more difficult, because there are few people around with them. I have yet to see one and they are around for several years.
I'm sorry if these considerations haven't been useful for you.
Monobazus - Thursday, March 29, 2012 - link
See this YouTube analysis of the Kindle DX with pdf's: http://www.youtube.com/watch?v=bVPBCD0GgBw&fea...adityarjun - Thursday, March 29, 2012 - link
Thanks you very much for your reply.It does seem as if neither of the two fit my needs perfectly. So I will have to make a compromise.
A 6" kindle or 7" tablet is out the question. It is just too small to read comfortably on.
The Kindle DX's screen and size seemed good to me but if you say that it can't handle pdfs comfortably then it is of no use to me. I will not be viewing any newspapers or magazines nor will I be surfing the net with it.
The only other option that remains is to use the ipad. The pros is that it should be able to handle large pdf *as per videos on youtube* as well as all my videos.
The con is the eye strain.
Is it really as bad as some sites make it out to be? Especially when compared to an e ink reader?
I will try to get my hands on an ipad and use it for a day or two but come to think of it, the screen cant be that much more stressful than a normal laptop, can it? And I have been reading reviews of the SoCs on Anandtech since morning...
Damn, I am really gonna go blind at this rate. *summons immense willpower and tries to close anandtech* * fails :-) *
mr_ripley - Thursday, March 29, 2012 - link
I keep and read all my technical pdf files on the ipad (textbooks, reports, memos, drawings, etc). I use an app called GoodReader which is absolutely amazing with all kinds of pdfs.Regarding eye strain, I usually keep my brightness setting at around 50% and zoom in to make the font large, which strains my eyes a little less and definitely less than a desktop screen. The sharp font on the new retina screen helps as well. That said I will admit it is not as easy on the eyes as an e-ink display.
tbutler - Thursday, March 29, 2012 - link
Honestly? I think the iPad's screen (even the first iPad, let alone the new one) gives me significantly *less* eyestrain than eInk, and I've owned a couple of Sony eInk readers.For me, the key eyestrain issue between the two is contrast. eInk displays are a light grey background with dark grey text, and in bright lighting the contrast is fine. But in less than bright lighting - for example, an indoor room without either a ceiling light fixture or multiple floor lamps - I start having trouble with distinguishing the text. Even a 40-year-old yellowing paperback is easier for me to read under those conditions. While you can use a clip-on reading light, I find that both clunky and less effective than it would be on paper.
The iPad (and really, any backlit LCD screen) has the 'stare into backlight' issue; but honestly, this is rarely a problem for me, and in particular it's much less of a problem than eInk contrast issues. Backlit color LCDs also wash out in bright sunlight, but not in even the most brightly-lit interior room, in my experience - however, for me this isn't a significant issue, since I spend much more time reading indoors than outdoors.
So just in terms of legibility, I'd pick the iPad (or the nook Color/Tablet) over any of the eInk readers I've used. And that's leaving out issues of software and PDF handling.