These older model HP's, circa 2010, were at their best, WIN 7 OS. That said, the BIOS is called Legacy. Older cards like the GTX 660 are excellent. But it needs a 500-600W PSU. It's also full height, and dual slot. How tall is the expansion rail?
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HP Envy 8 5010 Tablet (2) HP DV7t i7 3160QM 2.3Ghz 8GB Printer -- HP OfficeJet Pro 8620 Legal Custom Asus Z97D, I7-4790k, 16GB RAM, WIN10 Pro 64bit, ZOTAC GTX1080 AMP Extreme 3 fan 8GB RAM, 500GB SSD, Asus PB287 4k monitor, Rosewill Blackhawk case and 750W OCZ PSU.