In computing, an open platform describes a software system which is based on open standards, such as published and fully documented external application programming interfaces (API) that allow using the software to function in other ways than the original programmer intended, without requiring modification of the source code. Using these interfaces, a third party could integrate with the platform to add functionality. The opposite is a closed platform. In computing, an open platform describes a software system which is based on open standards, such as published and fully documented external application programming interfaces (API) that allow using the software to function in other ways than the original programmer intended, without requiring modification of the source code. Using these interfaces, a third party could integrate with the platform to add functionality. The opposite is a closed platform. An open platform does not mean it is open source, however most open platforms have multiple implementations of APIs. For example, Common Gateway Interface (CGI) is implemented by open source web servers as well as Microsoft Internet Information Server (IIS). An open platform can consist of software components or modules that are either proprietary or open source or both. It can also exist as a part of closed platform, such as CGI, which is an open platform, while many servers that implement CGI also have other proprietary parts that are not part of the open platform.