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In depth review: Apple's iPhone 4S running iOS 5

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S is for Speed

The opening argument in the case of "should I buy the new iPhone 4S, or just upgrade to iOS 5?" is performance. After just over a year of being on the market, the primary aspect of the iPhone 4 that needs addressing is its performance. While last year's phone is no slouch, no device can remain competitive with the passing of time under the rule of Moore's Law, particularly one that serves primarily a user interface for mobile computing.

About six months after iPhone 4 was released, competitors began talking about dual core mobile chips. RIM gambled its future on a new PlayBook OS derived from QNX that would minimally run on new dual core hardware, and its leadership spoke of dual core chips as if a proprietary feature that competitors wouldn't think of exploiting themselves.

Instead, a variety of Android licensees beat RIM to market with a number of tablets and smartphones using dual core processors, including the Nvidia Tegra 2 powered Motorola Atrix and Droid X2 phones and Xoom tablet and LG Optimus 2X smartphone; the Texas Instruments OMAP 4 powered Motorola Droid Bionic and (apparently) Google Nexus Prime (that's the same chip inside RIM's PlayBook tablet); the Qualcomm Snapdragon S3 powered HTC Sensation and Amaze (the same chip family used by HP's ill-fated TouchPad) and the Samsung Exynos powering that company's Galaxy S II.

All of these chips are variants of the dual-core ARM Cortex-A9 design. Apple debuted its own variant as the brain within iPad 2 this spring, named the Apple A5. When Steve Jobs unveiled the iPad 2, he declared it to the first tablet shipping a dual core chip in volume, a claim some took issue with until the sales results came in and ended any potential for arguing that Apple had any significant, viable competitors in the tablet market whatsoever.

Apple did not, however, bring the A5 chip to the iPhone until the release of iPhone 4S last week, the better part of a year after the first dual core smartphones were unveiled. The reason for Apple joining the dual core smartphone party so late appears to be tied to the fact that Apple sells a single, global product in huge quantities. Unlike Motorola, HTC and Samsung, which sell large numbers of low cost phones and a relatively small number of high end flagship devices, most of the phones Apple sells are its best model.

This puts Apple in the position of competing against the bleeding edge features of other platforms in the pages of the press, but against the prices of basic phones in the real world. For Apple to consistently match the latest high-end smartphone announcements of its competitors, it would have to adopt the same business strategy of pushing out a few fancy devices every couple months while continuing to sell large volumes of lower end devices at more affordable prices, a tactic Apple has also rejected in the PC market.

Apple's unique sales strategy for the iPhone has resulted in the company selling the most smartphones and earning the most revenues and--by far--the most profit, so its unlikely to change. That means you can expect the initial crop of smartphones to debut quad core chips, 2GHz speeds and Cortex-A15 chips not to come from Apple, but you'd be crazy to think Apple would be that far behind with a model more people would actually buy.

Apple A5, again

Just as when it was released this spring powering the iPad 2, Apple's A5 incorporates a dual core ARM Cortex-A9 MPCore paired with a dual core PowerVR SGX543MP2 graphics processing unit and 512MB of LPDDR2 system RAM.

The A5 chip built into iPhone 4S appears to be clocked at a variable speed around 800MHz, intended to save power over the full 1GHz speed of the part when used in iPad 2. Other compatible smartphones depict clock speeds as high as 1.2GHz, but as is the case with computers, additional gigahertz doesn't translate directly into performance or responsiveness. On the other hand, higher clock speeds do burn battery life as eagerly as large LCD screens, while performance and responsiveness are more tightly tied to the sophistication of a platform's software.

Apple does a better job delivering apparent speed and observable responsiveness with lower clock speeds by refining how the system makes use of available processing power, devoting a lot of attention to using the GPU to hardware accelerate the graphical user interface, accelerate general computing operations such as complex data processing (such as face detection in the camera) and efficiently using the least RAM possible, something that also further enhances battery life.

All of Apple's various optimizations actually result in the fact that, in general use, the iPhone 4S doesn't feel as much faster than the iPhone 4 as it actually is. Some apps open a bit faster, and when you're performing intensive tasks there can be a significant reduction in delays. It feels faster overall, but it doesn't feel twice as fast. But it actually is.

Faster chips mean fewer delays

As Apple advertises, the iPhone 4S is "quick and responsive, which makes all the difference when you’re launching apps, browsing the web, gaming, and doing just about everything."

In benchmarks, the iPhone 4S scores about twice as fast as iPhone 4 in integer and floating point performance, and about 20 percent faster in memory performance. In comparison to iPhone3GS, the iPhone 4 scored only about 27 percent faster in integer and floating point tests, and 32 percent faster in memory tests, despite having twice the RAM of the previous year's model (iPhone 4S has the same amount of RAM as iPhone 4, but uses a faster type of RAM).

Those score differentials are interesting because iPhone 4 felt dramatically faster than the iPhone 3GS it replaced. iPhone 4S feels faster, but the interface doesn't desperately need that much more speed to feel "snappy," so the huge boost in performance offered by the A5 isn't as obvious in basic use. Yes, it feels a little quicker overall, but the real difference is noticed when performing computationally intensive tasks.

For example, take a photo and you can apply an iOS 5 "auto-enhance" almost instantly, while iPhone 4 spends an additional second or two on it; the same momentary delay occurs when you save the photo. Little delays throughout your tasks seem to evaporate away.

Faster web pages, better looking games

One real world text for performance is the web browser. Rightmark's BrowserMark test indicates that iPhone 4 renders HTML and JavaScript 90 percent faster than iPhone 3GS, while the iPhone 4S is 67 percent faster than iPhone 4, running the same iOS 5.0.

In real world observations, loading a moderately complex site like the New York Times resulted in the page being visible almost immediately, rather than there being a slight delay of a few seconds as the page loaded. After becoming scrollable, the iPhone 4S page was also completely finished significantly sooner, while iPhone 4 kept filling out elements of the page for another two to three seconds.

In video games and other graphically intensive apps, GLBenchmark 2.1 scores paint a picture of faster, smoother graphics. The new iPhone 4S produced results that demonstrated performance increases from twice as fast to about seven times as fast as iPhone 4. This means the iPhone 4S will be able to run better looking games, just like the iPad 2's similar performance leap over the original iPad enabled it to produce higher quality graphics with better antialiasing (fewer jaggies) and better color depth at the same or better frame rates (for smoother animation).

Of course, to take full advantage of the improved graphics horsepower of iPhone 4S developers will have to tweak their games the same way they did to fully exploit the iPad 2 earlier this year. Being set to become the most popular iPhone yet means that developers are likely to actually do this.

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