Without the manual, you must locate the pins physically. Look for a block of pins usually located on the bottom-right edge of the board. It will typically have 9 pins arranged in two rows.
These boards were designed for cost-efficiency. d33d66 motherboard manual
He found the "System Board Layout" page, which labeled every tiny port. What he thought was a random slot was actually an M.2 PCIe SSD port, capable of making this old machine run like new. Without the manual, you must locate the pins physically
Because the D33D66 is not a major retail model (like an ASUS or Gigabyte board), finding the manual requires digging. Use these verified methods: Without the manual