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Inside Apple's iPhone 4S and its A5 CPU: 'S' is for Speed

The voice recognition technology and improved camera in Apple's iPhone 4S are made possible by the custom-built dual-core A5 processor that powers the handset.

Leading up to this Friday's launch of the iPhone 4S, AppleInsider will offer a closer look at some of the features of the next-generation handset. Given that the 'S' in the device's moniker was never officially defined by Apple, we offer five potential definitions. Today: 'S' is for Speed, thanks to the A5 processor.

Fastest phone on the market

Rather than get into technical specifications that are meaningless to most consumers and don't tell the whole story, Apple has not publicly revealed the clock speed or onboard RAM of the A5 processor that is found in the iPhone 4S. Instead, Apple has stated that the A5 is up to two times more powerful than the A4, and offers up to seven times faster graphics.

The A5 already debuted earlier this year in the iPad 2 with a variable clock rate around 1GHz, and 512MB of RAM, but evidence has shown the iPhone 4S processor has some slight differences to allow for improved battery life on the smaller device.

The A4 processor found in the iPhone 4 also had 512MB of RAM, while the A4 in the first-generation iPad had just 256MB. Initial speculation suggested the iPhone 4S would again double the iPad and feature 1GB of RAM, but tests have found it features 512MB, with the CPU clocked at 800MHz.

Of course, the real numbers that matter are benchmarks, and in those tests the iPhone 4S easily tops not only the iPhone 4, but the rest of the high-end smartphone market. AnandTech found that the dual-core A5 processor of the iPhone 4S earned a Geekbench score of 623, compared to a score of 360 for the iPhone 4.

That faster processing power is also evident when browsing the Web. Tests conducted with the iPhone 4S showed the hardware achieves a score of 89,567 in BrowserMark testing. That's 74 percent better than the existing iPhone 4, and higher than the Motorola Atrix 4G's score of 53,576.

In terms of graphics capabilities, the difference is far more striking. GLBenchmark 2.1 tests verified Apple's claims that the A5 offers graphics processing up to seven times faster than the A4 processor found in the iPhone 4.

A5 2
iPhone 4S CPU specs via Macotakara.

For example, in the GLBenchmark 2.1 Pro Offscreen test, the iPhone 4S and its SGX 543MP2 GPU earned a score of 122.7, while the iPhone 4 and its SGX 535 garnered just 15.3. The iPhone 4S score was also well ahead of the Samsung Galaxy S II, which earned 67.1, and the LG Optimus 3D, with a score of 42.6.

Delving back into the technical side, the iPhone 4S A5 has a BUS frequency of 200MHz, a L1 cache size of 32KB, and L2 Cache of 1024KB. In the iPad 2, the A5 BUS speed is 250MHz, while the A4 BUS speed of the iPhone 4 is 100MHz.

Console-quality graphics in your pocket

One of the greatest strengths of the A5 processor is its graphics processing capabilities. To highlight that, Apple at its iPhone 4S unveiling showed a glimpse of the upcoming title "Infinity Blade 2," the sequel to the best-selling iOS game from Chair Entertainment and Epic Games.

Epic is best known for making PC and console titles like "Gears of War" and "Unreal Tournament," but last year's release of "Infinity Blade" flexed some of the processing muscle of Apple's custom processors. But the A5 found in the iPhone 4S represents another huge leap forward for mobile gaming, Donald Muster, Chair Entertainment creative director, said in an interview with Eurogamer.

"As we've been working with Apple the last few weeks, I've had the opportunity to use the iPhone 4S quite a bit and, man, it's awesome," he said. "That A5 chip is pretty incredible. Having that much power in a device that small — really, there's a lot we can do with it."

With his team hard at work on "Infinity Blade 2," Mustard noted that the iPhone 4S will be capable of creating dynamic shadows on characters, and will feature dynamic light rays that shine through objects. He said the title looks "unbelievable" on Apple's next-generation handset.

"I'm still shocked that, with the iPhone 4S, I'm literally running around with a 1080p video camera in my pocket, with an 8-megapixel camera, 64GB of hard drive space and an A5 chip with 512MB of memory. This is a really powerful computer, right? That's going to allow us to do some really cool stuff for gaming."

"Infinity Blade II" will arrive on Dec. 1, 2011, and will be available only on Apple iOS devices.

Other third-party developers are also planning to take advantage of the added computing power in the iPhone 4S. Firemint's forthcoming "Real Racing 2" update will add 4-person split-screen gaming support to the iPhone 4S via AirPlay and the Apple TV.

The multiplayer functionality, demoed last week by the developer, requires the A5 processor found in the iPhone 4S and iPad 2. With it, the device will be able to host a game, and friends with compatible iOS devices can connect to the host, who will then stream the game data via AirPlay to the Apple TV.

This will allow up to four iOS devices to play a game on a big-screen 720p HDTV, as users steer their virtual vehicles with an iOS device. Using the A5 processor, developers will be able to bring console-style and quality gaming to the iPhone 4S.

8MP camera & Siri: Powered by iPhone 4S & A5

The faster speeds of the A5 CPU also allow for greater functionality on the iPhone 4S, with features that Apple says are not possible on previous-generation iPhone hardware. One software addition, already highlighted in the "Inside Apple's iPhone 4S" series, is Siri voice recognition.

With the additional power of the A5, the iPhone 4S and Siri will allow users to use their voice to execute tasks or obtain data. Siri allows users to dictate a message, find local restaurants, add or change calendar events, and even find information like weather or gas prices at in a specific town.

A5 3

Apple has said that Siri was developed alongside the A5-powered iPhone 4S, and the feature even relies on a data connection to Apple's servers for it to function.

The new processor also promises to greatly improve picture taking abilities with the iPhone 4S. Specifically, the added power is said by Apple to result in a blisteringly fast time to shoot, one that is claimed to be the fastest in the smartphone industry with "zero shutter lag."

While the camera itself has improved hardware for higher quality pictures, the A5 does more than process larger 1080p video and 8-megapixel photo files. The A5 processor also exclusively offers face detection when shooting still images, which allows the iPhone 4S to detect up to 10 faces in a single photo.

A5 4

With face detection, the iPhone 4S focuses on the most prominent face in a frame. The A5-powered system automatically balances exposure for the picture, resulting in improved picture quality.

Another addition new addition to the iPhone 4S is image stabilization when shooting 1080p video. Utilizing the A5 processor and the handset's gyroscope, the upgraded smartphone does real-time image stabilization when shooting video, resulting in less shakiness in a recording.

For more, see the previous installments of AppleInsider's "Inside Apple's iPhone 4S series:" 'S' is for Shutter, and 'S' is for Siri voice recognition.