It might be a silly question, however, why are the computer systems in the X.200 model, OSI, called open systems?

Note that I've read that open system is defined as "the representation within the reference model of those aspects of a real open system that are pertinent to OSI" and the real open system is defined as "A real system which complies with the requirements of OSI standards in its communication with other real systems." in the X.200 specification.

Thanks in advance.

2 Answers 2


I would assume that this is because the O in OSI stand for "Open".

Networking is about communication between many different kind of devices.
Using the word "computer" would be misleading, because the OSI model can be applied not only to computers, but to any kind of devices that is able to communicate over the network (routers, manageable swicths, automates, sensors, industrial machines...).

So they had to choose a term to describe any device using the model. The "system" word fit and is vague enough to cover all cases, and so to describe a system compliant to Open System Interconnection, the use "Open system" (which is shorter and more practical that "OSI compliant system")

only a guess tough, I don't think you'll get an authoritative answer from anyone else than the authors.

  • Thanks for the reply. By the way, if they wanted to model communicating systems, the ones you mentioned, Turing machines weren't a better choice? Any device or entity doing computations or communicate through a media can be seen as a Turing machine, as can be understood from the Church-Turing thesis. Oct 5, 2016 at 10:50
  • There's a little historical background here: networkengineering.stackexchange.com/questions/6380/…. A lot of it was in response to proprietary development by IBM, NCR, Burroughs, etc.
    – Ron Trunk
    Oct 5, 2016 at 11:43

They are connected using open protocols as opposed to proprietary protocols (open as per open source). Back in the day, each vendor had their own interconnect technology, such as IBM's SNA and DEC's DECNet phase IV. OSI was designed to replace that proprietary technology with one that different systems could use. In the event it was seen as too network-provider-centric and the pragmatism of IP ensured that IP became pre-eminent.

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