Going online to the Internet is relatively simple. All that is required is a browser and an Internet connection from an ISP. Communications within the enterprise is far more complex. Over the years, organizations have developed islands of computer systems, each with their own networking protocols and access methods. The enterprise has been faced with tying mainframes, midrange systems and desktop computers together for file sharing, electronic mail and routine data processing. Fortunately, companies around the world have for the most part adopted the TCP/IP and Ethernet protocols as "the" networking standards. Nevertheless, it is a daunting task keeping client machines running Windows and Mac OS X, as well as smartphones and tablets running iOS, Android, Windows Phone and BlackBerry with servers that run Linux, Unix, Windows and z/OS. See TCP/IP, Ethernet, enterprise networking, client/server, OSI model and standards.