NVIDIA GRID K1 Graphics Card

Hello,

I need purchase NVIDIA GRID K1 Graphics Card for Dell R720 Server.
Need to choose right item:

  1. NVIDIA GRID K1 R8RGR
  2. NVIDIA GRID K1 RF61J

What is the differency between above items?

Please let me know ASAP.

Thanks for your attention.
Omid Shirazi