Early iOS 8 Adoption Slower Than iOS 7, iOS 6

If you decided not to download iOS 8 when it became available yesterday — or simply didn't have enough free space on your device to do it — you weren't alone.

Initial adoption of Apple's new mobile operating system has been significantly slower than the last two versions - iOS 7 and iOS 6, early assessments have revealed. A full 24 hours after it was released, iOS 8 was running on some 7.3 percent of iOS devices in North America, according to new data from online ad network Chitika. That pales in comparison to iOS 7, which was installed on 18.2 percent of devices after its first day of availability, and iOS 6, which found its way onto 14.8 percent of Apple smartphones and tablets in 24 hours.

To come up with its adoption figures, Chitika examined a sample of millions of U.S. and Canadian impressions on its network between Sept. 17 and Sept. 18, and compared the iOS 8 growth rate to total iOS Web usage.

Mobile app tech platform Tapjoy backed up Chitika's analysis.

"Based on Tapjoy's network-wide data, which has a reach of over 200 million unique iOS consumers per month, iOS 8 is being adopted at a significantly slower rate than iOS 7," the company wrote in a blog post Thursday. While it took iOS 7 approximately 7 hours to reach 10 percent adoption, iOS 8 stands at less than 6 percent some 18 hours after its initial availability, Tapjoy's figures show.

The more tepid reception of iOS 8 is likely due to several factors, Chitika said, including the large file size of the update, which many users complained about on Twitter. The installation software requires more than 5GB of space to download over the air, meaning some users needed to delete a significant number of items off their device to install the update.

On top that that, the iPhone 6 and 6 Plus - which come pre-loaded with iOS 8 - don't arrive until Friday; Apple already logged a record 4 million pre-orders in the first 24 hours. And existing iPhone owners who plan to upgrade probably don't feel compelled to download iOS 8 on their current iPhone. Plus, not all iPhone users are eligible for the update.

"Perhaps most importantly, the pool of iPhones eligible to upgrade to iOS 8 is limited to iPhone 5s, 5c, 5, and 4s models, and many outlets have suggested that iPhone 4s users should not upgrade due to subsequent performance and functionality issues," Chitika said. "If most 4s users decide to stick with their current OS, then the maximum potential adoption of iOS 8 shrinks to just over 65 percent of the North American iPhone user base who use iPhone 5-type models."

You can also install iOS 8 on the iPod touch 5th generation, iPad 2, iPad with Retina display, iPad Air, iPad mini, and iPad mini with Retina display.

For more, see How to Get iOS 8 and Before and After iOS 8: What's Different?