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DECnet is a suite of network protocols created by Digital Equipment Corporation, originally released in 1975 in order to connect two PDP-11 minicomputers. It evolved into one of the first peer-to-peer network architectures, thus transforming DEC into a networking powerhouse in the 1980s.

Initially built with four layers, it later (1982) evolved into a seven layer OSI compliant networking protocol.

DECnet was built right into the DEC flagship operating system VAX/VMS since its inception. Digital ported it to its own Ultrix variant of UNIX, as well as Apple Macintosh computers and PCs running both DOS and Windows under the name DEC Pathworks, transforming these systems into DECnet end-nodes in a network of VAX machines. More recently, an open-source version has been developed for the Linux OS: see Linux-DECnet on Sourceforge. DECnet code in the Linux kernel was marked as orphaned on February 18, 2010[1]


Brief overview of the evolution of DECnet

DECnet refers to a specific set of hardware and software networking products which implement the DIGITAL Network Architecture (DNA). The DIGITAL Network Architecture is essentially a set of documents which define the network architecture in general, state the specifications for each layer of the architecture, and describe the protocols which operate within each layer. Although network protocol analyzer tools tend to categorize all protocols from DIGITAL as "DECnet", strictly speaking, non-routed DIGITAL protocols such as LAT, SCS, AMDS, LAST/LAD are not DECnet protocols and are not part of the DIGITAL Network Architecture.

To trace the evolution of DECnet is to trace the development of DNA. The beginnings of DNA were in the early 1970s. DIGITAL published its first DNA specification at about the same time that IBM announced its Systems Network Architecture (SNA). Since that time, development of DNA has evolved through the following phases:

Phase I (1974) Support limited to two PDP-11s running the RSX-11 operating system only, with communication over point-to-point (DDCMP) links between nodes.

Phase II (1976) Support for networks of up to 32 nodes with multiple, different implementations which could interoperate with each other. Implementations expanded to included RSTS, TOPS-10 and TOPS-20 with communications between processors still limited to point-to-point links only. Introduction of file transfer using File Access Listener (FAL), remote file access using Data Access Protocol (DAP), task-to-task programming interfaces and network management features.

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