Apple iPhone 4S: Thoroughly Reviewed
by Anand Lal Shimpi & Brian Klug on October 31, 2011 7:45 PM EST- Posted in
- Smartphones
- Apple
- Mobile
- iPhone
- iPhone 4S
The A5 Architecture & CPU Performance
The original iPhone debuted with a single 412MHz ARM11 core built on a 90nm process. The 3G improved network performance in 2008 but left the SoC untouched. It wasn't until the iPhone 3GS in 2009 that the SoC got a major performance and power update. Apple moved to a 65nm process node, a brand new ARM Cortex A8 based SoC and an upgraded GPU. The A4 released in 2010 once again gave us a process shrink but kept the architecture unchanged.
Apple's A5 SoC
Apple's A5, first introduced with the iPad 2, keeps process technology the same while introducing a brand new CPU and GPU. The A5 integrates two ARM Cortex A9 cores onto a single die. The improvement over the A4 is tremendous. At the single core level, Apple shortened the integer pipeline without reducing clock speed. With a shorter pipeline the A5 gets more done per clock, and without decreasing clock speed the A5 inherently achieves better performance at the same clock. The move to the Cortex A9 also enables out-of-order instruction execution, further improving architectural efficiency. I've heard there's a 20% increase in performance per clock vs. the Cortex A8, but combine that with the fact that you get two A9s vs a single A8 in last year's design and you get a pretty big performance increase.
There are several situations where the A5's two cores deliver a tangible performance benefit over the A4's single core. Like Android, iOS appears to be pretty well threaded. Individual apps and tasks can take advantage of the second core without a recompile or version update. The most obvious example is web browsing.
Mobile Safari is well threaded. Javascript rendering can be parallelized as well as parts of the HTML parsing/rendering process. All of the major Javascript performance benchmarks show a 60 - 70% increase in performance over the A4, which is partially due to the availability of the second core:
This translates directly into faster page load times. As you can see in the video below, the iPhone 4S (left) loads the AnandTech front page over WiFi in about 5 seconds compared to 9 seconds on the iPhone 4 (right). That's really the best case scenario, the improvement in the next page load time was only about a second (7s vs 8s).
Typical improvements in load time fall in the 10 - 70% range, contributing significantly to the phone feeling snappier than its predecessor. To quantify the improvement I ran through our standard web page loading suite, a test that hits AnandTech, CNN, NYTimes, Engadget, Amazon, Digg and Reddit hosted locally on our lab's network. The average page load time over WiFi for all of the pages is below:
While web page rendering is a natural fit for multiple cores, I was surprised by how poorly threaded some apps ended up being. For example, although I did see performance improvements in exporting edited videos from the iOS version of iMovie, the gains weren't always evident. A quick profile of the app revealed that much of the export process is still single threaded. Just as we've seen on the desktop, there will be some added work necessary to get all apps to utilize multiple cores on iOS.
It's not always performance within an app that saw improvement with the A5: application install and launch times are also much quicker on the 4S. The time to launch Epic's iOS Citadel demo went from 32 seconds on the iPhone 4 to 22 seconds on the 4S. While the iPhone 4 may feel fast enough for many users, the 4S is noticeably faster.
Much of the faster feel comes from by shaving off of seconds here or there. For example, I noticed apps like Messages pop up just slightly quicker on the 4S and you'll see your listing of messages a hair faster than you would on the 4. In the video above you get a brief idea of the sort of subtle improvements I'm talking about. YouTube launches a fraction of a second quicker on the 4S vs the 4.
These subtle decreases in response time are simply icing on the cake. The move from a 4 to a 4S is one of those upgrades that you'll notice right off the bat but will really appreciate if you go back to an iPhone 4 and try to use it. If you do a lot of web browsing on your phone, you'll appreciate the 4S.
I wasn't entirely sure whether or not I could attribute all of these performance improvements to the faster CPU. It's possible that some of the tests I mentioned are IO bound and Apple could have used faster NAND in the 4S. To find out I rounded up a bunch of iPhone 4Ses at all available capacities and measured sequential write speed:
Apple uses multiple sources for NAND so it's possible that you'll see these numbers move around a bit depending on your particular phone. It looks like the iPhone 4S' NAND is no faster than what Apple shipped last year - at least in sequential write speed. The target appears to be 20MB/s and Apple does its best to stay around there. My iPhone 4 is actually pretty quick at 22MB/s but the advantage isn't significant enough to make a huge deal about. I don't have a good way of measuring random IO performance yet but application launch time is largely governed by sequential IO so I don't expect we're seeing gains from anything outside of the CPU and memory bandwidth in the earlier tests.
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doobydoo - Friday, December 2, 2011 - link
Hardware wise, the difference between the iPhone 4S CPU/GPU combination and Android competitors, is huge.If you want the best performance, I don't see any other way to turn.
As for the software, I like most users would happily use Android or iOS - they've largely converged anyway.
name99 - Friday, November 4, 2011 - link
"If you had a 4 already your just a "moop" if you upgraded to one of these!"OK, so most US customers on on a 2yr plan. Upgrading for them is impractical, if for no other reason then for carrier reasons. And then you are COMPLAINING that Apple produced an upgrade that (in your eyes) gives them no reason to upgrade???
What exactly is your problem? You're like someone who goes to a restaurant and complains "the food sucks --- and the portions are too small".
dennykins - Tuesday, November 1, 2011 - link
Hey! I have that "Introduction to Modern Optics" book too! Pretty old, but still relevantname99 - Tuesday, November 1, 2011 - link
"It is admittedly curious that Apple hasn’t decided to make some other larger change to distinguish the 4S from the other two"There was, of course, also precious little visual change between iPhone, iPhone3G and iPhone 3GS. Likewise for plenty of other upgrades across the Apple line in the last ten years. I don't know why Anand thinks it's strange. For YEARS Apple has made the point that you buy an iMac --- and you get the what Apple thinks an iMac should be today. You don't buy an iMac XV371. You don't buy an iMac 7. You don't buy an iMac 20011. You buy an iMac --- which may or may not look like its predecessor, which may or may not have last been updated three, six or
nine months ago.
It's obvious that Apple wants to bring that same mindset to phones (and iPads). Screwing with people's expectations of an update in July was simply the first step in breaking the mindset of a particular schedule for upgrades. Of course there are issues that make it more difficult to do this cleanly, for example carrier involvement and the ridiculous subsidized pricing model --- which means that Apple has reason, at least for now, to keep older models around. But there are obvious advantages to Apple in switching to this model, including
- not being forced to release SW too soon. I think we'd all agree iOS5 was released under pressure, and that iOS 5.1 will be the release 5.0 should have been.
- Apple's been able to ignore pressure from a stream of constant Android updates for the past two years, but at some point annual upgrades may just be too slow. At that point it would be nice to have the option of minor upgrades (cf the recent PowerBook Pro upgrades), say boosting the CPU from 800 MHz to 1GHz, without it being a big deal --- something to shut up the crowd that looks at specs, while being ignored by the mass audience that does not care about specs and doesn't want Apple talking about them.
Not that this will stop haters from claiming that "people buy iPhones for fashion"....
KPOM - Tuesday, November 1, 2011 - link
Good observation about the upgrades. Yes, it's entirely possible we'll see minor spec bumps as the iPhone has become a staple of Apple's product line. We don't notice all the the upgrades in the Android world (how many people know or even care about the differences between the Galaxy S, Galaxy S II, and Galaxy S II Skyrocket ?), partly because they happen all the time.Also, Apple has never been a company to change the design simply for the sake of change. They tweak a design until they "get it right," but then stick with it a while. This year's MacBook Air, for instance, is a big update from last year's (Core i5/i7, backlit keyboard, 4GB RAM standard on most models), but they didn't change the external design. It's still selling extremely well and received good reviews. I think it's the same with the iPhone. The 4S has some significant improvements, from the faster processor, better camera, and better antenna.
name99 - Tuesday, November 1, 2011 - link
I'm glad you guys adopted my suggestion to report how snappy a phone feels, based not only on CPU benchmarks but also on the speed of flash, and things like the launch time of apps.In the spirit of constant complaint that is the web, can I now ask that you continue to do this for all future phones, not just iOS devices.
Yes, you have fanboi readers who care only about how wonderful their platform is; but you do also have a number of honest readers who are genuinely interested in things like how the speed of flash (including the speed of SD flash) varies across devices, and how launch times (for comparable apps) vary --- which, of course, depends on both HW and also SW/OS decisions.
Drasca - Tuesday, November 1, 2011 - link
There's a small typo that I'm surprised no one else has caught. Perhaps I am the only one that cares enough about this particular subject enough to. On the last page, 4th to last paragraph, we see:"we’ll hopefully see the technology mature into something more like what years of science fiction moves have promised us."
I believe you mean movies here.
I caught it in particular because I've been discussing amongst my friends how modern technology is the future promise of older science fiction. Oh gosh gee wiz, we have instant mobile communication across the globe, including video! We talk into our portable devices and they think for us. These devices are an extension of ourselves. In a way, we've become like the borg in that we're connected to community at large. Facebook is a form of hive mind group consciousness. Heck, we can track each other near-instantaneously and some folk are vividly aware of each other's locations.
These are interesting times, and what has only previously been explored as supposition has become reality.
I still want my flying cars and teleporters. Also, Holodecks and the AI behind it. Plus, the bridge of the starship enterprise D with its big comfy captain's chair and massive screen.
anishannayya - Wednesday, November 2, 2011 - link
If you want an iPhone, you really don't have a choice. Either you get the 4S or go find an Android phone.shashank7040 - Wednesday, November 2, 2011 - link
Asus Eee Pad being the first tablet With Slide out QWERTY........http://goo.gl/B4rJUthevibenow - Wednesday, November 2, 2011 - link
Check out our review of the Iphone 4shttp://www.youtube.com/watch?v=35v1kkaPM9s