ntral controllers. Changes should of course be tested in isolated parts of the network or data centers before they are implemented. See Chapter 4, "Managing Broadband Networks," for software-defined network technologies on broadband links. Network Operating Systems LAN Network Operating System (NOS) software is located on specialized computers called file servers in the LAN. File servers provide shared access to programs on LANs. A NOS-also referred to simply as the operating system (OS)-defines consistent ways for software to use LAN hardware and for software on computers to interoperate with the LAN. LAN operating system client software is located on each device connected to the LAN. The way PCs request access to services such as printers, e-mail, and sales applications located on servers is defined by operating systems. A network operating system also defines how devices access shared applications and the network. A NOS further controls how icons are displayed on computers' "desktops." Examples of network operating systems include Novell, Windows Server 2010, Windows Server 2016, Sun Solaris 10, and Linux. www.TechnicalPDF.com Client software (software on nodes) is installed on individual devices. Examples of client software on PCs include Windows XP, Windows 8, and Windows 10. Apple computers use various operating systems such as OS10.5 and OS10.14.2. Often when client software on Windows and MAC computers are upgraded, older Office and other applications need to be upgraded. Features in the upgraded operating system may not be compatible with older word processing and spreadsheet software. Data Centers-Centralized Locations for Housing Applications A data center is a physical location where an organization or cloud provider's data applications are centralized. This includes LAN operating systems, e-mail servers, security software on dedicated servers or appliances, voice telephony, storage area networks, databases, and accounting applications. See Figure 2-3 for a depiction of a data center. An appliance is 