microphone
there are two microphone connectors, one on the front and one on the rear of the computer. connect a microphone to this connector to record sounds onto the hard disk or to use speech recognition software.
line in
there is one line-in connector on the rear of the computer. the computer receives audio signals through this connector from an external audio device.
line out
there are two line-out connectors, one on the front and one on the rear of the computer. the computer sends audio signals through this connector to powered speakers with built-in amplifiers, headphones, a multimedia keyboard, or the audio line-in connector on a stereo system. the internal speaker in your computer is disabled when any device is attached to either the front or rear line-out connector.
connecting devices to the front line-out connector disables the rear line-out connector.