In the Open Systems Interconnection (OSI) communications model, the presentation layer ensures that the communications passing through are in the appropriate form for the recipient. For example, a presentation layer program may format a file transfer request inbinary code to ensure a successful file transfer. Programs in the presentation layer address three aspects of presentation:
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- Data formats - for example, Postscript, ASCII, or binary formats
- Compatibility with the host operating system
- Encapsulation of data into message "envelopes" for transmission through the network
An example of a program that generally adheres to the presentation layer of OSI is the program that manages the Web's Hypertext Transfer Protocol (HTTP). This program, sometimes called the HTTP daemon, usually comes included as part of an operating system. It forwards user requests passed to the Web browser on to a Web server elsewhere in the network. It receives a message back from the Web server that includes a Multi-Purpose Internet Mail Extensions (MIME) header. The MIME header indicates the kind of file (text, video, audio, and so forth) that has been received so that an appropriate player utility can be used to present the file to the user.