The topic of open systems as it relates to the needs of libraries to establish interoperability between dissimilar computer systems can be clarified by an understanding of the background and evolution of the issue. The International Standards Organization developed a model to link dissimilar computers, and this model has evolved into consensus standards. The American library community has also developed a standard for interoperability, referred to as Z39.50. An operating system called Unix, developed by AT&T, is often specified as the system that can handle future software. Although there are benefits to the standard Unix, it is less efficient than some proprietary systems, and it lacks networking standards. Today computer manufacturers are beginning to make sure that their operating systems will comply with the new Portable Operating System Information Exchange (POSIX), a new standard developed by the U.S. government. Although librarians have already established a standard for interoperability, care must be taken to insure that vendors comply with the standard. It is concluded that the library's focus should be on linking systems without becoming too concerned about the operating system that a particular system uses. A list of CISC- and RISC-based hardware and compatible operating system software is appended, and a glossary is provided. (KRN)