Lenovo ThinkCentre M57p 6073 Hardware Installation And Replacement Manual page 15

Connector
USB connectors
Ethernet connector
Serial connector
Parallel connector
Audio-line-in connector
Audio-line-out connector
Description
Used to attach a device that requires a Universal Serial Bus
(USB) connection, such as a USB keyboard, USB mouse, USB
scanner or USB printer. If you have more than eight USB
devices, you can purchase a USB hub, which you can use to
connect additional USB devices.
Used to attach an Ethernet cable for a local area network
(LAN).
Note: To operate the computer within FCC Class B limits, use
a Category 5 Ethernet cable.
Used to attach an external modem, serial printer, or other
devices that use a 9-pin serial connector.
Used to attach a parallel printer, parallel scanner, or other
devices that use a 25-pin parallel connector.
Used to receive audio signals from an external audio device,
such as a stereo system. When you attach an external audio
device, a cable is connected between the audio line out
connector of the device and the audio line in connector of the
computer.
Used to send audio signals from the computer to external
devices, such as powered stereo speakers (speakers with
built-in amplifiers), headphones, multimedia keyboards, or the
audio line in connector on a stereo system or other external
recording device.
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Chapter 2. Overview