Open architecture is a type of computer architecture or software architecture that is designed to make adding, upgrading and swapping components easy.  For example, the IBM PC and Apple have an open architecture supporting plug-in cards, while the Apple IIc and Amiga 500 have a closed architecture . Open systems architecture May use a standardized system bus Such As S-100 , PCI or ISA or They May Incorporate a proprietary standard bus Such As That used on the Apple II, with up to a dozen slots that allow multiple hardware manufacturers to produce add-ons, and for the user to freely install them. By contrast, closed architectures, if they are expandable at all, have one or two “expansion ports”, or they may be installed by technicians with specialized tools or training.
Computer platforms may include systems with both open and closed architectures. The Mac mini and compact Macintosh are closed; the Macintosh II and Power Macintosh G5 are open. Most desktop PCs are open architecture, purpose nettops are Typically closed.
Open architecture allows potential users to see all of them.  Typically, an architecture that integrates the developer or integrator wants to share. The open business processes involved with an open architecture may require some license agreements between entities. Open architectures have been successfully implemented in many different fields, including the US Navy . 
- Open network architecture for equal-access
- Open-source software for software that can be modified and rebuilt
- Open-source hardware
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- Jump up^ “The HOW and WHY of OPEN ARCHITECTURE” .