HTC has already released the certification of Android 6.0 Marshmallow to its One M9 devices to support the official software's roll out to the smartphone. The update carriers a host of new key features and improvements in battery management, storage, connectivity, functionality and user interface.

HTC One M9 smartphones near official over-the-air (OTA) update of Android 6.0 Marshmallow, as it is now in the certification process. Being the most exciting update in software history, Android 6.0 Marshmallow will come to One M9 after the release to its predecessor, One M8.

As of the moment, One M8 will first get the Marshmallow update, while One A9 is the only HTC device to be launched with Android 6.0 out of the box.

Previously, Jason Mac of HTC first revealed on Twitter that the Taiwanese giant's plan for Marshmallow. First speculations told that December 2015 might be the release date for the phones but it never came. However, custom ROMs based on the build were made available to these devices.

Meanwhile, One M9 smartphones are expected to get the update later this month. The device is currently in certification process, wherein Google provides source code to HTC and its chipset manufacturer to incorporate Android to HTC's own operating system.

Android 6.0 Marshmallow brings in two major improvements in Android Run Time (ART) and flex storage.

The Android Run Time gets prominent improvements since its debut in Android 4.4 KitKat, when it was still an optional feature. With Lollipop, the Android RT revolved with a Default setting instead of Dalvik cache to advance performance and help manage RAM usage. With Marshmallow, the feature will improve the performance of the device and also helps control battery consumption. In the first maintenance release of Marshmallow, the feature is expected to bring more improvements.

Flex storage is a combined storage feature for internal and external space, which makes it applicable only to devices with micro SD slot. With Marshmallow, it can format external memory card and pool to internal storage so that users can utilize to install apps and app data. However, slower memory card may trigger a low speed warning.