MTS. At the University of Michigan (UM) and Wayne State University (WSU) there was a parallel development effort by the Merit Network to develop network support. The Merit nodes were PDP-11 based and used custom hardware and software to provide host to host interactive connections between MTS systems and between MTS and the CDC SCOPE/HUSTLER system at Michigan State University (MSU). The Merit nodes were known as Communication Computers (CCs) and acted as IBM Control Units on the one side while providing links to other CCs on the other side. The initial host to host interactive connections were supplemented a bit later by terminal to host (TL) connections, and later still by host to host batch connections which allowed remote jobs submitted from one system to be executed (EX) on another with printed (PR) and punched card output (PU) returned to the submitting system or to another host on the network. The remote batch jobs could be submitted from a real card reader or via *BATCH* using a #NET "card" at the front of the job. Merit renamed its Communication Computers to be Primary Communication Processors (PCPs) and created LSI-11 based Secondary Communication Processors (SCPs). PCPs formed the core of the network and were attached to each other over Ethernet and dedicated synchronous data circuits. SCPs were attached to PCPs over synchronous data circuits. PCPs and SCPs would eventually include Ethernet interfaces and support local area network (LAN) attachments. PCPs would also serve as gateways to commercial networks such as GTE's Telenet (later SprintNet), Tymnet, and ADP's Autonet, providing national and international network access to MTS. Later still the PCPs provided gateway services to the TCP/IP networks that became today's Internet. The Merit PCPs and SCPs eventually replaced the Data Concentrators and Remote Data Concentrators at the University of Michigan. At their peak there were more than 300 Merit PCPs and SCPs installed, supporting more than 10,000 terminal ports. Virtual environments UMMPS provides facilities that allow the creation of virtual environments, either virtual machines or virtual operating systems. Both are implemented as user programs that run under MTS. The initial work on the first MTS virtual machine was done at the University of Michigan to simulate the IBM S/360-67 and allow debugging of UMMPS and MTS. Later the University of British Columbia did the initial work to create a S/370 MTS virtual machine. In theory these virtual machines could be