This is a genuine Dell motherboard model for OptiPlex GX520 DT (Desktop). 

All motherboards have been tested and checked for good capacitors, are fully guaranteed to arrive in working order, and warranted for 90 days.
 

• Intel 945G Express Chipset
• Socket 775 Supporting Pentium 4 and Celeron Processors
• 533/800 MHz system bus
• 2 - DIMM DDR2 SDRAM sockets
• 4 GB MAX system memory
• Integrated Intel Graphics Media Accelerator 950
• Integrated 10/100/1000 Lan
• Integrated Sound
• Serial ATA  Controller
• One Floppy Connector
• 2 PCI Card Slot
• 6+2 USB 2.0 Ports
• Audio Ports for line-in, line-out, and microphone
• 1 Serial/1 Parallel Port

Equivalent Dell parts: X7841, MD573, RJ290, PJ479, XG312, UG982

*  Dell usually has several different part numbers for the same part.  You may receive a part number that is different from the one listed.