What's the use of a 2nd PCI-E x16 slot ?

pcle x16 slot   Dan pcle slot

A PCIe x8 card will fit in any PCIe x8 or PCIe x16 slot PCIe cards larger than the PCIe slot may fit in the smaller slot but only if it is open

your i5-3470 works on PCIe natively, Optiplex 7010 has only one slot bound to CPU PCIe, others are linked via chipset  List of Motherboards with 4 PCI-Express x16 Slots: ASUS Pro WS TRX50-SAGE WIFI, GIGABYTE A620M C, GIGABYTE B650M C V2, ASUS Prime B760M-A AX, GIGABYTE B760M

sparky slot machine 1 x PCI Express x16 slot, supporting PCIe and running at x16 * The PCIEX16 slot shares bandwidth with the M2C_CPU connector  You can install PCI Express slots in larger slots but not smaller ones For example, you can install a PCI Express x1 adapter into an x16 slot (but will still