Apple released iOS 6.1 to its legions of iPhone, iPad and iPod Touch owners earlier this week. The software, made available Monday afternoon, was installed on 21.8% of iOS devices within 36 hours, according to Onswipe.

Onswipe develops mobile websites and tracks about 13 million iOS device users across its sites each month. Its data suggested that iOS 6.1 had reached 11.3% of iOS devices within 24 hours of its release and 21.8% within 36 hours. It hasn't updated its data to reflect the adoption rate 72 hours after the software update was released.

iOS device users have been quicker to adopt iOS 6.x in general since its release in September of last year. According to Apple marketing VP Phil Schiller, iOS 6.x has been installed on about 300 million iOS devices. Apple says that it has sold 500 million iOS devices since 2007, so iOS 6.x has reached an adoption point of about 60%. That's quite impressive.

[ Apple's stronghold on the tablet market is starting to weaken. Read Apple's Tablet Rivals Gaining Share. ]

Onswipe CEO Jason Baptiste believes the faster uptake of iOS 6.x is due to the fact that Apple now allows system updates to be downloaded and installed over the air. Prior to the arrival of iOS 5 in 2011, iOS device owners had to connect their iOS device to a computer to update their system software. Now, they can pull the updates out of the air.

It's notable, too, because iOS device owners are far more likely to update their system software than are Android device owners. This is one aspect where Apple's system software model is superior to Google's.

With Android devices, official software updates need to be approved by the wireless network operator. Gaining that approval often takes months. Since its July 2013 release, only 10% of Android devices have been updated to Android 4.1 Jelly Bean. The number of devices using Android 4.2 Jelly Bean, which was released in October, is much smaller.

iOS 6.1 added few new features to the operating system. The official change log says the software now lets device owners purchase Fandango movie tickets via Siri. It also fixes bugs, adds LTE support to more carriers and makes iTunes Match more reliable across devices.

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