iPhone 6 and iPhone 6 Plus are available on discount on popular retailer sties like Best Buy and Target. Reuters

Apple fans are predicting the iPhone 6S will prove bigger than the iPhone 6. But what exactly are the features that will roll out with the device? As Apple is silent on the subject and will remain so until the actual unboxing, the best source of clues on this respect, according to Business Insider, is the soon-to-touch-down iOS 9.

As replacement for the iOS 8, the Apple mobile operating system will have a grand preview next week at the 2015 Worldwide Developers Conference. But leaks already indicate how different the iPhone 6S will be from the iPhone 6.

New Look

The jump from iOS 8 is not expected to be that huge, but Apple is reportedly unpacking a new set of OS themes and wallpapers with the iOS 9. Likely joining the existing options for iPhone users are the green and blue color pattern.

Enhanced iMessage

In the current iOS, text messages sent to another iPhone generate an alert, when activated, that says the message has been received and read. In iOS 9, recipients will be given the option to filter who will and will not get these notifications.

Secured File Syncing

Apple has indicated that syncing of files between mobile devices and desktop computers will be protected by a tougher security protocol. This is because of the shift from IMAP-based servers to the iCloud Drive as the engine behind the background task in iOS 9.

Split Window

Viewing two application windows at the same time has been a perk long enjoyed in the Windows platform and will be further improved with the release of Android M. Even before the iPhone 6 came out last year, split-window or multitasking has been rumored as an iOS feature, which could finally happen once iOS 9 is unleashed. There were suggestions that split-window is designed exclusively for the large-screen iPad, but they remain unconfirmed.

Wi-Fi Security

Said to be packed with iOS 9 is a feature called Trusted Wi-Fi. This function is for iPhones and iPads to instantly detect wireless routers and connect to them when determined to be safe. For risky connections, automatic encryption will be used to ensure protection.

Siri Made Smarter

Google Now has tech experts raving, and all the more when Cortana was introduced by Microsoft, seemingly overshadowing Apple’s Siri. The digital assistant created by Apple is reportedly getting a major makeover in time for iOS 9. Most of its functions and features will be deeply integrated with core iOS apps to better perform tasks that it will handle.

Re-engineered Apple Maps

Google Maps getting the better of Apple Maps led to the ouster of Apple executive Scott Forstall a few years back. Apple aims to change that by beating Google Maps in the latest Apple Maps incarnation.

Jailbreak Breaker

Starting with iOS 8, jailbreaking the iPhone was made more difficult and Apple is ramping up on its efforts to deter hackers from modifying its latest operating system. The tech giant seems highly confident that when the iOS 9 becomes official, jailbreaking will be thing of the past.

Most of these features are likely to get confirmation when the 2015 WWDC kicks off Monday. And the actual test drives should come next following the iPhone 6S release date, pegged by analysts to happen between September and October this year.