In the Open Systems Interconnection (OSI) communications model, the physical layer supports the electrical or mechanical interface to the physical medium. For example, this layer determines how to put a stream of bits from the upper (data link) layer on to the pins for a parallel printer interface, an optical fiber transmitter, or a radio carrier.
The physical layer is usually a combination of software and hardware programming and may include electromechanical devices. It does not include the physical media as such.
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- The Recommendation X.200...Open Systems Interconnection - The basic reference model can be ordered for a small fee from the ITU-S.