What makes Apple’s iPads and iPhones feel so zippy?

October 9, 2013, 3:35 PM UTC

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FORTUNE — Here’s a graphic you can expect Apple (AAPL) to trot out at its next iPad launch event — reportedly set for Oct. 22.

It’s a performance chart created by Agawi, an app streaming company that developed an open-source tool for measuring touchscreen response times. In a report issued Tuesday, Agawi compared how long (in milliseconds) the flagship tablets of six leading manufacturers took to respond to a touch on the screen.

“Basically we found that Apple’s iOS performed nearly two times better than Android,” Agawi co-founder Rohan Relan told the Guardian. “The findings were surprising to me because Samsung makes the hardware, but it was the worst by a large margin in our tests.”

Touchscreen responsiveness — or latency — is one of those things Apple (AAPL) works hard to achieve and doesn’t get much credit for, mostly because minimum average response times (MARTs) are not usually benchmarked.

But that responsiveness is part of what makes iPads — and iPhones, which Agawi tested last month — so much fun to drive. It may not matter much if all you’re doing is reading or watching videos. But typing on a laggy touchscreen is no fun at all.

How does Apple do what it does? Last month, Agawi offered two theories:

“Since touchscreen hardware has significant latency itself… our best guess at Agawi is that Apple’s touchscreen hardware is better optimized or more sensitively calibrated for capturing and processing touch. Another possibility is that while the Android and [Windows Phone 8] code are running on runtimes (Dalvik and CLR respectively), the iPhone code is written in closer-to-the-metal Objective-C, which may reduce some latency.”

In Tuesday’s report, Agawi added this:

“Our previous speculations continue to apply —  more responsive devices may process touches earlier in the stack, poll for touches more frequently or have touchscreens optimized or calibrated to be more responsive. In our latest review of our test apps, we discovered an optimization that suggests that the GPU or GPU drivers in the devices might also add significant latency.”