[Users] The machine type of one cluster

Hi all: There is a "machine type" in cluster, It will decide which machine of Qemu will be used, When we add the first host into cluster, a default machine type is shown. We can correct the DB's value of the engine to set the machine type. I just want to know how dose cluster choice the default machine? It is decided by VDSM? Qemu? or It is only fixed value in engine's DB? Regard Kewei