Comment by pjmlp

No, the whole UI runs on the client machine, which in X Windows nomenclature is the server.

The client application (on X Windows nomenclature), runs on the remote server and is headless.

Instead of sending streams of bytes to render text, it sends streams of encoded X Windows commands to draw the UI.

Everything else regarding compilers, subprocesses and what have you keeps running on the server, regardless how the connection is made.

Think big X Windows terminals or green/ambar phosphor terminals accessing the single UNIX server, used by the complete university department.