iOS 9, the latest operating system of Apple, will be released on Wednesday. Some tech enthusiasts don't see much difference between iOS 7 and iOS 8, that's why this upgrade is much-awaited.

Before anything else, what are those Apple devices that are eligible for an iOS 9 upgrade? According to ExtremeTech, the gadgets that will be receiving the update are iPhone 4S, 5, 5s, 5c, 6, and 6 Plus, together with the brand-new iPhone 6S and 6S Plus.

The latest Apple operating system can also support iPod Touch fifth and sixth generation. Plus, iPad 2 up to the new iPad Pro and the entire iPad Mini series are supported.

First on the list of the new features included is the notes. The application used for taking down quick notices has been updated so that the user can now sketch the notes, add pictures and maps, USA Today reported.

Second, iOS 9 reportedly has a low power mode. This will enable the user to save battery, promising to add another hour or so to the device without plugging it.

Third is security — not that the previous ones are less secure. The thing is, Apple is changing the four-digit security code to six, making it a little bit harder to crack.

Proactive search, wherein Apple provides information based on the user's location and app, and News App, which can deliver customized news depending on the user's interest, are also included in iOS 9.

App Thinning is also included. This will reportedly free up the space on the devices by downloading the version of application the device can only run.

iOS 9 will reportedly get updates and features centered for games. It includes GameplayKit, Model I/O and ReplayKit.

The decision on upgrading to iOS 9 depends on the user's preference. If ever an upgrade has to be done though, it is important for the user to check the device's compatibility first, then have the files backed up in either iCloud or iTunes, as per CNET.