Windows Embedded 8.1 Pro is the full version of Windows 8.1 Pro but with embedded licensensing. The embedded licensing allows you to ship the operating system pre-installed and pre-activated together with your embedded application to your customer.

Windows 7 for Embedded Systems allows you to use all the features of Windows 7 on your embedded device. You can choose between Windows 7 Professional for Embedded Systems and Windows 7 Ultimate for Embedded System depending on what features you need.
Use new features such as Multitouch, DirectAccess, VHD boot with Windows 7 for Embedded Systems.

Windows XP Professional for Embedded Systems is the easiest way if you need to switch from Windows XP Professional to Embedded because they are identical in terms of functionality and setup. Only the licensing terms are different.