The frontend process (mythfrontend) is responsible for anything that requires interaction such Watching Recorded Programs or Watching Tv. It provides the GUI you use on your TV/Monitor as well as the LiRc, keyboard, or other input handling for Frontend Navigation. In addition, any MythTv Modules, or plugins, that are installed execute on the same machine that the user is interacting with. As such, the hardware requirements for a frontend are those necessary to support these features. Underpowered machines may not have enough processing power to decode recordings in software while the same machine could perform these functions if hardware decoding is available.
The MythTV architecture supports a theoretically unlimited number of frontend processes connecting to backends. A frontend process can run on the same machine as a backend in the instance of a combined machine, but is often found running on smaller, quieter, more stylish hardware since it the piece of equipment that usually sits within view of the user. When used on a separate machine from a backend, the frontend process connects over a network, either wired or wireless. It communicates with the backend to retreive the Electronic Program Guide and recorded content which is either streamed to the machine or directly accessed if the frontend has access to the same HardWare/File Storage the backend does.
The frontend process also has the widest platform support. Frontends have been ported to the Xbox and MacOSX (see the Myth On Mac Osx guide) as well as the standard Linux Distros with additional work being done to port it to Windows under Cygwin.