When running on iPhone 3G, iOS 4 disables multitasking, background wallpapers, Bluetooth keyboard support, and a "data protection" feature. The first generation iPhone and iPod touch can't run iOS 4 at all; those early devices make up less than 10% of the entire number of iOS devices sold (a number that will hit 100 million by the end of June, Apple noted at WWDC).
Apple's three years of OS upgrade support for the first generation models compares favorably with other platforms, where devices are often unlikely to ever see an update. For example, Google's Android OS, which has delivered software updates that are at least on par and often better than most other competing platforms, stopped supporting new updates for the original T-Mobile G1 after a single year.
The HTC myTouch 3G was released in the US less than six months before Android 2.0 was unveiled, but still hasn't received that release yet, let alone the newest 2.2 update, which is currently only available to users of the Google-branded Nexus One. Even many recent Android phones won't be able to update to the latest Android 2.2 right away once it becomes officially available.
Apple has worked to push all of its mobile users to the latest version of the operating system as soon as possible after its release, making it available as a direct download from iTunes rather than relying upon the various mobile operators to distribute it over the air, as Google's Android, Nokia's Symbian, RIM's BlackBerry, HP's webOS, and Microsoft's Windows Mobile platforms have to do.
No multitasking for iPhone 3G in iOS 4
Deactivated support for iOS 4 multitasking on the iPhone 3G is believed to largely be a product of its limited memory; like the original iPhone, it only has 128MB of system RAM. Unlike the first iPhone, Apple continued to sell the model over the past two years, making its support for iOS 4 critical to moving the majority of the installed base to the latest version of the operating system.
Jailbreakers have noted that previous versions of the iPhone operating system could "support multitasking" in the sense of simply working around the app launching boundaries Apple erected. That results in an implementation of multitasking that works more like Android, where there is no effort to regulate how background tasks work in order to conserve battery life.
Apple's new multitasking APIs in iOS 4 enable a variety of background operations, state saving, and notification alternatives that together result in better battery life and largely automatic process management that doesn't require users to manually hunt down and kill rogue or unwanted apps in the background.
Apple's engineers determined that supporting this more sophisticated level of multitasking on models with less RAM than the iPhone 3GS wouldn't work well, so rather than excluding iPhone 3G users from upgrading, they simply turned off multitasking as a feature so users could benefit from the other improvements to iOS 4 (which as a whole also take up more memory than previous versions of the OS).
On page 2 of 2: iOS 4 eats up RAM, No wallpaper, Bluetooth keyboards for iPhone 3G in iOS 4 .
iOS 4 eats up RAM
Developers report that iOS 4 uses a lot of RAM. In an article comment, Hrissan notes, "IÂve looked at the list of processes & their real memory usage in Xcode for my iPhone 3G after launching and quitting a large game (to make iOS free as much memory as possible).
Daemons for features switched off:
Â BTServer: 684KB (I have bluetooth off)
Â accessory: 550KB (I never use accessories)
Â lockdownd: 1.56MB (Monitoring activation status Â I have an unlocked
ÂÂ*ptpd: 1.29MB (Tethering, I have tethering off)
Also look at these 2 daemons:
Â aosnotifyd: 2.6MB (Mobile.me sync Â so much for 1 open socket?)
ÂÂ*dataaccessd: 3.74MB (Exchange calendar sync Â oh my God!)
"I love new iOS 4 features, but it seems memory optimization was not the top priority. It is possible even that supporting 3G was decided on the later phase of development."
No wallpaper for iPhone 3G in iOS 4
While the increased memory requirements of iOS 4 multitasking are easy to understand, some have questioned why Apple doesn't support background wallpapers on Home screens. One user who emailed Apple's chief executive Steve Jobs about the issue got a characteristically terse reply (as noted by Gizmodo) stating, "The icon animation with backgrounds didn't perform well enough."
While jailbreakers have been putting background images on the Home page of the iPhone for years, Apple's implementation of wallpapers is more sophisticated, using drop shadows to isolate icons and their text labels from the underlying graphic to improve their appearance and readability. The new iOS 4 also renders shadows under the icon dock.
Apple found that doing this on the significantly slower iPhone 3G resulted in a significant slowdown that made it perform badly enough to simply drop the feature rather than ship something that either looked bad or felt slow and jerky. Jailbreakers report that activating wallpapers on the iPhone 3G under iOS 4 does indeed result in sluggish performance.
No Bluetooth keyboard support for iPhone 3G in iOS 4
Deactivated support for iOS 4's Bluetooth keyboard feature is also a hardware issue. The first two generations of iPhones supplied basic Bluetooth 2.0 support. Starting with the iPhone 3GS, Apple added Bluetooth 2.1 + EDR (Enhanced Data Rate) capable hardware.
The newer specification improves device setup with the "Secure Simple Pairing" mechanism and implements "Extended Inquiry Response," which reduces power consumption in low-power mode.
Enhanced encryption in hardware
Data protection is a new feature in iOS 4 that "enhances the built-in hardware encryption [of the iPhone 3GS and 3rd generation iPod touch] by protecting the hardware encryption keys with your passcode," according to an Apple tech support article.
"This provides an additional layer of protection for your email messages and attachments. Third-party applications can use the data protection APIs in iOS 4 to further protect application data."
The original iPhone and iPhone 3G along with the first two generations of iPod touch lack hardware support for data encryption, so none of them could support the new feature that improves upon it either. The iPhone 3GS' hardware encryption was recently the subject of reports that assailed the feature as "worthless."