This paper discusses the design and implementa-
tion of a parallel GUI Service in Tessellation OS and
its capabilities to provide soft service-time guarantees.
We show that the GUI Service's parallel architecture
allows it to take advantage of multiple processors to re-
duce the overall service times for client requests. We
also show that the GUI Service properly utilizes CPU
bandwidth reservation to meet the time requirements
of all its clients for scenarios in which traditional win-
dow systems fail to do so.