There are only two days to go before Apple Inc.’s (NASDAQ:AAPL) Worldwide Developers Conference, or WWDC, where the company is expected to announce iOS 8, its next major update to its mobile operating system. A research firm found that iOS 7 adoption has achieved new levels among iPhone and iPad users in the U.S. and Canada.

According to a new report from Chitika, an ad network, 89.7 percent of U.S. and Canadian iPhone web traffic is generated by users running some version of iOS 7. While iPad usage figures did not quite match the adoption rate on iPhones, iOS 7 users still constituted the vast majority of total U.S. and Canadian iPad web traffic at 84.8 percent.

“To quantify this latest study, Chitika Insights analyzed tens of millions of U.S. and Canadian iOS-based online ad impressions generated from May 22 through May 28, 2014. The results were then split into OS version distributions for iPhone and iPad users, respectively,” the research firm said.

iOS7-adoption-iPhone iOS 7 adoption rate among iPhone users in North America. Photo: Chitika Insights

Chitika’s last study on the same subject from February showed that 84.3 percent of iPhone owners were running iOS 7, meaning that the number rose 5.4 percentage points over the past quarter ending in May. At the same time, iPad usage share increased from 78.5 percent, representing a growth of 6.3 percentage points.

iOS7-adoption-iPad iOS 7 adoption rate among iPad users in North America. Photo: Chitika Insights

Chitika also mentioned that prior to WWDC in 2013 iOS 6 represented 92.7 percent of iPhone web traffic, while for iPads the percentage was 82.9 percent. The lower share for iPhone in 2014 may be attributed to issues some users reportedly dealt with as part of iOS 7.x updates, which might have led a small percentage to stick with iOS 6.

Meanwhile, the comparatively higher share for iPad this time around is possibly due to the fact that iOS 7 compatibility extended to all iPads, except for the original 2010 model, according to Chitika.

Apple is expected to introduce the new iOS 8 on Monday at the WWDC, with banners for the upcoming OS are already going up at the Moscone Center in San Francisco,  AppleInsider reported.