K20X vs K20Xm

What is the difference between K20X and K20Xm?

I believe that the ‘m’ means passive cooling, or at least that is difference between the K20c and the K20m.

So if that is right, then you may need some additional fan/cooling system for that GPU.

K20X and K20Xm are the same GPU. There is no actively cooled version of K20X, only the passively cooled K20Xm model.

K20 comes in a K20c and K20m variant, the m is passively cooled, the c has an active fansink.