It is the connector for the OPTICAL cable to plug into.
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the optical drive will connect to the power supply with a
connector called molex connecter it is a 4 prong connector
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A Molex Connector connects to optical drives and hard
drives.
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sc connector means subscriber connector and st connector means
straight tip connector
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The RadioShack Digital Optical Cable Connector comes with a
limited 90-day warranty from the manufacturer. RadioShack stands
behind their products, so you should have nothing to worry
about.