Editing Systems Network Architecture (section)

===Physical Unit (PU)===<!-- IBM Network Control Program redirects here -->
*PU1 nodes are terminal controllers such as [[IBM 6670]] or [[IBM 3767]]
*PU2 nodes are cluster controllers running configuration support programs such as [[IBM 3270|IBM 3174]], [[IBM 3270|IBM 3274]], or the [[IBM 4701]] or [[IBM 4702]] Branch Controller
*PU2.1 nodes are [[peer-to-peer]] [[IBM Advanced Peer-to-Peer Networking|(APPN)]] nodes
*PU3 was never defined
*PU4 nodes are front-end processors running the [[IBM Network Control Program|Network Control Program]] (NCP) such as the [[IBM 37xx]] series
*PU5 nodes are host computer systems<ref>{{cite web |last=Microsoft |title=Physical Unit (PU) |url=http://msdn.microsoft.com/en-us/library/ee253218%28v=bts.10%29.aspx |access-date=September 7, 2012}}</ref>

The term [[37xx]] refers to IBM's family of SNA communications controllers. The 3745 supports up to eight high-speed [[Digital Signal 1|T1]] circuits, the 3725 is a large-scale node and [[front end processor|front-end processor]] for a host, and the [[IBM 3720|3720]] is a remote node that functions as a [[concentrator]] and [[router (computing)|router]].