Android (operating system) store, and by September 2013, one billion Android devices have been activated. , the Google Play store has over 2.7 million Android applications published, and , apps have been downloaded more than 65 billion times. The operating system's success has made it a target for patent litigation as part of the so-called "smartphone wars" between technology companies. Android devices account for more than half of smartphone sales in most markets, including the US, while "only in Japan was Apple on top" (September–November 2013 numbers). At the end of 2013, over 1.5 billion Android smartphones have been sold in the four
Network operating system Network operating system The term network operating system is used to refer to two rather different concepts: Network operating systems can be embedded in a router or hardware firewall that operates the functions in the network layer (layer 3)."" Early microcomputer operating systems such as CP/M, DOS and classic Mac OS were designed for one user on one computer. As local area network technology became available, two general approaches to handle sharing arose. In a peer-to-peer network operating system users are allowed to share resources and files located on their computers and access shared resources from others. This system is