This is not a hard and fast rule, and some operators do have additional rules such as 21 days out of 28, 28 out of 42, as well as a maximum number of days offshore in a year, depending on the type of installation.
Windows Embedded Automotive is a variation of Compact for embedded systems in cars. Windows Embedded Pro is designed for intelligent systems: machines with embedded Internet-connected devices that gather data, analyze it and communicate with other systems. Windows Embedded Standard is a modular operating system that allows users to make choices about various implementations within their environments. Windows Embedded Handheld is designed for portable devices like those used in retail, manufacturing and delivery companies. Windows Embedded Enterprise is for embedded systems in industrial devices. Windows Embedded Server and Windows SQL Server for Embedded Systems.
Windows Embedded Standard is available in different versions. The license you need depends on which features you are going to use in your image. Note: Windows Embedded Standard 7 Service Pack 1 will introduce new SKU Compliance Feature Packages. These packages ease the selection of a specific version. For example, when a WES7E SKU Compliance Package has been added only the features which are included in this package will work.