Fleet management software is used to supervise, manage, locate, schedule and maintain vehicle fleets. Comprehensive maintenance and logistics systems may feature a modular architecture with integrated applications for activities such as asset management, maintenance requirements, planning and forecasting, configuration management, and defect analysis. Asset management involves tasks such as the definition of individual assets and asset families, cost analysis and valuation, and calculating depreciation. Maintenance requirements describe scheduled maintenance activities such as A, B, C, and D checks. Typically, fleet management software for the aviation industry allows users to track work done against airworthiness directives (AD), service bulletins (SB), and engineering orders (EO). Software for the transit industry should support department of transportation (DOT) guidelines. With fleet management software, planning and forecasting activities may include line maintenance planning, work packaging, estimating, capacity planning, and supply chain management. Line maintenance planning is especially important in the aviation industry, where remote shops or stations may need to service aircraft that are in-transit. Work packaging allows users of fleet management software to combine different maintenance requirements, sometimes on different assets, to complete work in the most efficient way. Estimating is an important module for users of fleet management software who have budgetary, accounting or financial oversight activities. For organizations with large fleets of vehicles, capacity planning can be critical. Supply chain management (SCM), though typically a function of enterprise resource planning (ERP) systems, is also available with some fleet management software. Selecting fleet management software requires an analysis of system architectures and operating systems. Web-based applications do not require the installation of fleet management software on employee workstations, personal computers (PCs), or handheld devices such as personal digital assistants (PDAs), tablet PCs, and pocket PCs. Instead, employees use a browser to connect to a remote web server. Most PC-based applications use the Microsoft Windows operating system, client/server architecture, and network protocols such as Ethernet or token ring. Standalone products such as fleet productivity applications may also be available. Some fleet management software runs under the MacOS operating system. Other products use Linux. Microsoft and Windows are registered trademarks of Microsoft Corporation. MacOS and Apple are registered trademarks of Apple Computers, Inc. Linux is a registered trademark of Linus Torvalds.