CNET

The latest version of Apple's mobile operating system, iOS 9, may be causing a lag in performance on some iPhones, mostly on older models.

Videos on YouTube channel iAppleBytes that compare the performance of iOS 9.0.1 vs. iOS 8.4.1, the previous version of the mobile OS, on some older iPhones do show a difference in speed, though it isn't dramatic. The videos, posted Wednesday, show that in the new version apps take a bit longer to open. Also, switching between apps is a bit slower and, in general, navigating around the screens drags slightly.

A few users chiming in on Apple's support forums have complained that iOS 9 has slowed down their phones. Some said their iPhone 6 is slower, while one person said the iPhone 5C now lags after the iOS 9 upgrade.

A poll conducted by tech publication 9to5Mac on Friday, two days after iOS 9 was released, asked "How has iOS 9 affected your iPhone?" Out of the 27,725 people who voted, 36 percent said their iPhone was significantly slower after the update, while 31 percent said it was a little bit slower after the update.

Does Apple have a crisis on its hands? Probably not. Some iPhone 6 users have griped about slow performance, but the lag likely affects older iPhones the most, which isn't uncommon. A new operating system offers new features and updates to existing features, some of which require a more powerful processor and can chew up more battery life. As one example, some users have turned off virtual assistant Siri's new app prediction features to try to speed up the phone, according to The Guardian.

As usual, different people are having different experiences.

One user on Apple's support forum said: "Immediately after upgrading my iPhone 6 Plus to iOS 9 I noticed major lagging -- definite increase in slowness. I've restarted the phone several times and it does seem to be getting better, but it's definitely not where it was with iOS 8."

Another said: "Have to say, I too have a 6, and have not noticed any lag at all. Everything works just as it should, apart from a few initial bugs that now appear to have resolved themselves."

On the plus side, the videos from iAppleBytes show that Siri is faster to respond.

Performance can certainly vary based on which features you use, which ones you enable or disable and which may be running in the background. The company continues to fine-tune its latest mobile OS. Apple issued iOS 9.0.1 on Wednesday and has already released a beta of 9.1 for developers. But users of older devices may just have to get used to the slight lag time.

Apple did not immediately respond to CNET's request for comment.