We all know that the AMD Radeon HD 7000 series is extremely power efficient. Having said that it comes at a cost. This power efficiency comes due to the new electrical interface featured in PCIe v3.0 and 2.0 slots and is ABSENT in PCIe v1.1 slots. Hence they are NOT COMPATIBLE.

Online interaction with AMD technical staff Personal interaction with technical staff from MSI They all clearly stated that that PCIe v3.0 cards are not compatible with v1.1 Further to prove their point MSI was even kind enough to provide a reference card they had with them, i.e the HD 7850 and it did not work on my computer's motherboard featuring PCIe x16 v1.1 slot. Just to make sure I installed the card correctly I placed another card from Nvidia i.e GTX 560 onto the board that I got from a friend and everything worked flawlessly.

Does that mean the compatibly of PCIe slots is broken? NO!

This whole scenario where the cards did not seem compatible featured only AMD cards. I did not tell you anything from Nvidia. Here is the twist. Most of us would agree when I say that Nvidia cards like GTX 600 series use much more power than the HD 7000 series. The question is why does it consume so much power? This was explained to me carefully by a head of technical staff of Nvidia (India) by stating "Our cards seem to draw more power because we have tried to maintain THE COMPATIBILITY OF PCIe slots of newer generation with the older ones"

Well... it does make sense I guess, my 560Ti worked in a 1.1 slot I did just to see what would happen because according to this

1.1 slots and provides higher bandwidth of the PCIe v.30 slots. Even all the reference cards from Nvidia of the 600 line up were able to run on PCIe v1.1 slots. This even answers why the GTX 500 series never used PCIe 2.1 interface like the HD 6000 series. Because remember the PCIe 2.1 is exactly similar to PCIe 3.0 and the only difference is the 'Bandwidth'