What are the USB ports on motherboards?

Abhishek 55

Honorable
Apr 14, 2013
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What are they really ??
What is there use?

Does it have any connection with the USB 2.0 ports on the cabinet????\

I am planning to buy this motherboard-
http://geb.ebay.in/g/ImportHubViewItem?itemid=200835237451&ASRock-FM2A75M-DGS-FM2-AMD-A75-FCH-DDR3-SATA3-USB3-0-Micro-ATX-Motherboard-MB

But i have this cabinet-
http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=c01815020&lang=en&cc=us&contentType=SupportFAQ&prodSeriesId=3942799&prodTypeId=12454

The motherboard supports USB 3.0 but cabinet has only 2 USB 2.0 slots.
Is it backwards compaitable???