HTC One M8 features a 5-inch 1080p display, 2.3 or 2.5 GHz Snapdragon 801 CPU/GPU, 2GB of RAM, enhanced “BoomSound” speakers, a 2600mAh battery, up to 32GB of internal storage and support for external microSD cards up 128GB. One of the most unique features of the HTC One (M8) is its new “Duo Camera.” This camera features two sensors: one Ultrapixel sensor and one depth of field sensor to allow users to select the image focus after the picture has been taken.
It will take some time for HTC to roll out the official Android Marshmallow update for One M8. Till then you can install custom ROMs to taste Marshmallow. CM 13 is one such ROM which will update HTC One M8 to Android 6.0. Follow the guide below.