A computer system (usually a mainframe) that controls interactions between itself and a set of connected computers. A host system makes operating systems and applications available by way of Host Integration Serverÿ2004 to computers running software for terminal emulation or for APPC. In SNA terminology, a host is capable of sending an ACTPU command to HIS 2004. A host may also set up a PU-SSCP session with HIS 2004.