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 IIe have an open architecture supporting plug-in cards, whereas the
Apple IIc and
Amiga 500 computers have a
closed architecture. Open architecture systems may use a standardized
system bus such as
S-100,
PCI or
ISA or they may incorporate a proprietary bus standard 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" using a proprietary connector design that may require a license fee from the manufacturer, or enhancements may only be installable by technicians with specialized tools or training.