With its new iPhone 4S scheduled to go on sale in two days, Apple on Wednesday released the iOS 5, the latest version of its mobile operating system for iPhone, iPad, and iPod touch devices. In addition, the company released Mac OS X 10.7.2, an update that includes Safari 5.1.1 and support for iCloud, which also opened for business on Wednesday.

iOS 5 is particularly important for Apple because it addresses areas where iOS devices have lagged behind Android devices, such as wireless syncing and updates, and because it enables the use of Apple's iCloud service, a key strategic initiative and major investment for the company.

Apple says that iOS 5 includes more than 200 new features. These are the nine that matter.

Software Updates Over Wi-Fi.

Android users have long enjoyed wireless syncing and software updates. Apple had to catch up and finally has. The need to connect one's iOS device to one's computer with a cable only serves to remind users how iOS limits them. Good riddance.

Camera Software Improvements

You can now launch the iPhone/iPod touch 4th generation camera by double clicking the home button. And you can take a picture using the Volume Up button. Score one for simplicity. The software update also adds optional grid lines to help frame shots, pinch-to-zoom support in the preview screen, the ability to swipe to the camera roll from the preview screen, and the ability to tap and hold to lock focus and exposure. (The iPad 2 and iPod touch 4th generation support only exposure lock, not focus lock.)

[ Apple's iPhone 4S arrives on Friday, October 14. Is it worth considering? ]

iCloud Support

While iCloud is not well-suited for backing up lots of data--Apple offers only up to 50 GB--users with a modest number of images and media files should find the service a convenient way to make their files available across all of their iOS and Mac OS X Lion devices. Certainly it's better than the old method--syncing via cable to iTunes and dragging copied files out of iTunes to one's desktop.

iMessage

With iMessage, you can send an unlimited number of text messages, at no cost other than your time, to other iOS 5 users. Best of all, you don't have to change your texting habits--iMessage in build into the Messages app.

Notifications

The Push notification system that arrived in iOS 3 has been greatly improved. Instead of the intrusive modal dialog boxes that used to pop up, Notifications now appear briefly as banners atop the screen. The messages can then be viewed in the Notification Center, accessible from any app by swiping down from the top of the screen.

Reminders

Apple's version of a To-Do List is important because Reminders are location-based and work across iCal, Outlook, and iCloud. Thus a Reminder to stop by the pharmacy on the way home would appear on your iPhone as you pass the pharmacy. Reminders can be set using Siri, the new voice recognition software available on Apple's forthcoming iPhone 4S.

Twitter Integration

Now you can sign into Twitter once and tweet from a variety of apps, including Camera, Maps, Photos, Safari and YouTube. And thankfully, Apple hasn't made existing Twitter clients redundant.

Under Hood

Along with visible improvements to Apple's Mail and Calendar iOS apps, there are many new capabilities in iOS 5 that aren't readily evident. A lot of these have to do with how iOS devices interface with corporate IT systems. For example, IT administrators can now disable email forwarding to prevent company messages from being sent to external accounts. They can also turn off syncing with iCloud or iTunes, thereby limiting the replication of files on personal systems.

New APIs

Apple is introducing 1,500 new developer APIs, which allow third-party developers to take advantage of iOS 5 improvements. So in the months ahead, expect to see a lot of apps that integrate with iCloud and other Apple services.

iOS 5 requires an iPhone 3GS, 4, or 4S, an iPod touch 3rd or 4th generation, or either of the two iPad models released to date. It's available through iTunes.

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