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It may be that PVR backends support only Kodi clients as a frontend for it, but most PVR backends can both Kodi as well as other frontend applications/devices.In those cases where a single PVR backend it setup for the sole purpose of serving multiple frontend clients then that PVR backend is commonly refereed to as "PVR server".
Logically, the Live TV and PVR functions in Kodi uses a distributed application structure that is designed after the client–server model concept which consists of two parts, these two parts are also refereed to as frontend and backend: This concept follows a separation of concerns design principle, with the "PVR backend" as such being a separate application/process that directly interfaces with your physicial TV-tuner adapter(s) or controller(s) that recieves the broadcast television signal into your house in your house and performs the actual task of tuning, streaming, and recording over-the-air and cable television signals and radio programming.
PVR backends can either run on the same host/device running Kodi, or run on a stand-alone host/device on your local home network completely by itself (as a server) with Kodi only running when needed, as long as they have a network connection between them.
Kodi as a frontend can support multiple PVR backends at the same time, and also some PVR backends may be able to serve several clients simultaneously.
These appointments will be a single event which will start and finish on the same day.
In addition users will be able to mark their unavailablity in the calendar due to personal commitments.