iOS 4 is compatible with iPhone 4, iPhone 3GS and iPhone 3G, as well as recent generation iPod touch. Multitasking is only available with iPhone 4 and iPhone 3GS. iOS 4 also comes preinstalled on the new, $99, 8GB iPhone 3GS, as well as the next-generation iPhone 4, set for release this Thursday.
The build released Monday is 8A293, the same as the gold master release candidate introduced to developers at the iPhone 4 event last week. The full IPSW update file weighs in at 579MB and is available through iTunes.
New features of iOS 4 highlighted by Apple:
Multitasking: Now you can run your favorite third-party apps —- and switch between them instantly —- without slowing down the performance of the foreground app or draining the battery unnecessarily.
Folders: Organize apps into folders with drag-and-drop simplicity. Get faster access to your favorites and browse and manage up to 2160 apps.
Even better Mail: See messages from all your accounts in a unified inbox, organize messages by threads, open attachments in third-party apps, and more.
iBooks: More than a great ebook reader, iBooks is also an amazing place to browse and shop for books, day or night.
Create playlists: Create custom playlists right on your iPhone.
5x digital zoom: Get closer to your subjects by zooming in up to 5x.
Tap to focus video: While shooting video, tap the display to choose where to focus.
Faces and Places in Photos: View photos based on who’s in them and where they were taken.
Home screen wallpaper: Change the background wallpaper on your Home screen.
Gift apps: Send apps as gifts to your friends or family.
Spell checking: A built-in spell checker works in Mail, Notes, and other apps.
Wireless keyboard support: Pair a keyboard based on Bluetooth wireless technology with your iPhone.
For more, see First Look: Apple's iOS 4 for iPhone, iPod touch.