According to an investigation by Blaze, iOS 5 hugely improves browsing on Apple hardware. Barely mentioned by Apple on its own website (the Safari section of the iOS 5 features page simply mentions that iOS 5 "improves Safari performance on all your iOS devices"), changes include a massive boost to HTML5 performance, faster JavaScript performance, and persistent cache for home-screen apps.
The Sunspider benchmark results will be particularly heartening to developers eschewing the App Store in favour of web apps: the performance of home-screen apps comes close to matching that in Safari, unlike in iOS 4, where home-screen apps were much slower. "For Home Screen Pages, it's clear that the Nitro engine is now being used," explains the Blaze article. "JavaScript performance improved dramatically in those apps, though it still lags a bit behind MobileSafari itself. Our guess is that the Nitro engine is indeed used, but some of its optimizations are disabled, presumably for security reasons."
The article also has an iOS 4 vs. IOS 5 face-off, demonstrating massive speed improvements in Microsoft's 'HTML5 Speed Reading' demo. iOS 4 lagged, with an embarrassing 2 FPS, comparing very unfavourably with Windows Phone 7's 24 FPS and the Nexus S's 10 FPS. In iOS 5, an iPhone 4 now tackles the test at 40 FPS, due to the system's GPU-accelerated rendering.
Blaze notes that iOS 5 also introduces HTTP Pipelining, scraps downloading CSS files alongside other resources, and improves caching for home-screen apps. Blaze's conclusion is that iOS 5 is "good news for mobile web performance", despite some drawbacks relating to the aforementioned CSS bottleneck and also a surprising regression in UIWebView JavaScript performance.
