Only after one week after the launch of the iOS 9, is that Apple made available the new version (iOS 9.0.1) that fixes some bugs of the previous version. This update fixes a number of issues, including alarms and timers, as well as the Safari browser and videos in the application of photos.
Apple is doing everything to make the 9 version as light as possible, compared to 8 released last year. And the adherence has matched the expectations because, as it was recently reported, it reached 50% in the days following the launch.
