Open architecture means an architecture whose specifications are public. This includes officially approved standards as well as privately designed architectures whose specifications are made public by the designers. The opposite of open is closed or proprietary.
The great advantage of open architectures is that anyone can design add-on products for it. By making an architecture public, however, a manufacturer allows others to duplicate its product. Linux, for example, is considered open architecture because its source code is available to the public for free. In contrast, DOS, Windows, and the Macintosh architecture and operating systemhave been predominantly closed. Many lawsuits have been filed over the use of these architectures in clone machines. For example, IBM issued a Cease and Desist order, followed by a battery of lawsuits, when COMPAQ built its first computers.