There is no such thing as a HD 7800 graphics card. There are a series of HD 7800 cards, which one do you have ? The choices will be different if you have a laptop. Please furnish the information required > https://community.amd.com/thread/196209
Use GPU-Z 'Lookup' function.
Yep, and I remember that dxdiag would show my 7970 as 7900 series.