What is physical layer?

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.