Samsung Galaxy S4 has a 5″ 1080p Super AMOLED display (PenTile 441 ppi), a pseudo octa-core Samsung Exynos 5410 or quad-core Qualcomm Snapdragon 600 (depending on region), 2 gigs of RAM, up to 64 gigs of storage, and a 2600 mAh battery. Furthermore, the device features additional features such as floating touch and a 13 MP shooter featuring a revamped camera interface.
There is still no visibility on when Samsung Galaxy S4 will get Marshmallow update. Leaks have suggested it will take around middle of next year. Instead of waiting till then, you can install CM 13 ROM which will update S4 to Android 6.0 Marshmallow. Follow the guide below.