Overclock.net › Articles › The final answer to the controversial PCIe x16 version compatibility.

The final answer to the controversial PCIe x16 version compatibility.

I will attempt to once and for all solve this controversial question about whether PCIe slots are 'REALLY' backward compatible or not.
All the information I am providing are from official sources and by that I do not mean some random 'So called' local experts. They were collected from official various motherboard and graphic card manufacture's technical staff and personal testing, experimenting and experience.

Let me start by telling all of you how I came about doing all this research and finally got a valid answer to it.
It all started when I was researching for a new graphic card for myself. I was on a budget so I needed a good mid ranged card providing the performance I need. After comparing and doing lot of research I settled down for a GTX 560 (Non ti) but it was still pushing the limits of my budget!
Then I started looking on the AMD/ATI side for a card that suits me the best and came across the HD 7770. It just seemed perfect for my needs.
This was all until I realized it needed a PCIe x16 v3.0 slot. I had a motherboard with PCIe x16 v1.1 slot.

Now we all know that PCI SIG is famous for designing the newer versions of PCI express slots which were backward and forward compatible with all the versions previously made. Until they introduced PCIe x16 v2.1, after which they chain of backward compatibility was reported broken.
On various forums there were instances of people having trouble with their PCIe v2.1 graphic cards not running on PCIe v1.1 slots.

Now was this true? Why was the backward compatibility for PCIe slots broken?
Reading the article on Wikipedia and after having a chat with the PCI SIG's tenchical staff I was explained how the thermal and electrical designs were changed in PCIe v2.1 slot apart from the higher bandwidth speeds.
PCIe v2.1 had all the features of the latest PCIe v3.0, like the thermal and electrical designs, power usage protocols etc. but featured the same bandwidth speed of PCIe 2.0.

Now most of you people out there never need to worry about your card having compatibility issues with your motherboard because almost all motherboard released after 2010 have PCIe x16 v2.0 slots. So this article is not aimed at these users as all PCIe v3.0, v2.1 and for that matter of fact any PCIe version of card is compatible with PCIe v2.0 slots.
This article is for those few people like me who still use PCIe v1.1 slots and have a doubt about the compatibility with the newer cards like Nvidia GTX 600 series or AMD/ATI Radeon 7000 series.

So I started researching various forums to find an answer to one of controversial question on Internet regarding computer components, "Is PCIe x16 v3.0 compatible with PCIe x v1.1 slots?"
Some sites and forums and the members in them claimed that all of them are backward and forward compatible while some claimed that they are not.
What was to be believed?
Off course it is hard to believe what people generally say on forums and you really need a solid source to make your decision. This is when I came across this little review on techpower.com: http://www.techpowerup.com/reviews/Intel/Ivy_Bridge_PCI-Express_Scaling/24.html
Reading that article pretty much made me sure that yes they are all backward and forward compatible and I dont have to worry about which version of PCI Express the card uses.

I decided to get the Sapphire Radeon HD 7770 OC edition but just before I made my purchase I thought checking with the vendor (i.e Sapphire) once just so that I could have some peace of mind. That is when my hopes were shattered when Sapphire's online technical staff told me that their HD 7770 needs at least PCIe x16 v2.0 slot to function properly.
Off course I don't mean to say that the article on techpowerup.com was false, it was perfectly legit but what I did not realize is that they tested those cards all of PCIe x16 v3.0 slot!
Just at different bandwidths and by scaling down the verions of PCIe slots to test those cards. At the end of the day they still used a perfectly build PCIe x16 v3.0 slot which featured all the newer thermal and electrical designs and the technology called 'SCRAMBLING' for encoding which was absent with the older PCIe version like the 1.1 which uses 8b/10b encoding scheme for that purpose.

Now on one side the sources like Wikipedia (http://en.wikipedia.org/wiki/PCI_Express#PCI_Express_2.1) and the technical staff of Saphhire told me that PCIe x16 v3.0 is not compatible with PCIe v1.1 slot.
While on the other side various forum members, the PCI SIG (http://www.pcisig.com/news_room/faqs/pcie3.0_faq/#EQ6) stated that they are all backward and forward compatible.

So what is the truth? ARE THE PCIe SLOTS BACKWARD AND FORWARD COMPATIBLE?

The answer is 'YES' and even 'NO'. Confused? Keep reading...

While it is true that PCI SIG while developing PCI express slots made sure that they remain compatible with each other, it is the GRAPHIC CARD manufactures (i.e Nvidia & AMD) and the sub vendors (Saffire, Zotac, EVGA etc) that really make the difference!
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.
Sources of proof: Online interaction with Sapphire technical staff
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"
That is to say that the Nvidia cards featuring PCIe v3.0 are fully backward compatible with PCIe v1.1
This explains why Nvidia cards are so power hungry. It is because the 'PCIe interface' in these cards is similar to that of PCIe 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'
Sources of proof: Personal Interaction with Nvidia's head of tenchincal staff (India)
Zotac Website (http://www.zotac.com/index.php?option=com_virtuemart&Itemid=100313&lang=en) and an online interaction with them.

I also personally tested the Nvidia GT 640 on the same rig the AMD card was tested on and I did not have any problems what so ever.

So to most of the people who own the motherboards having chipset X38 and latter you have both AMD and Nvidia choices open to you.
But to the few people like myself owning a motherboards with G41 and previous chipsets the only solution seems to be Nvidia.

Note: Read this info about which Northbridge chipset supports what version of PCI Express (http://en.wikipedia.org/wiki/List_of_Intel_chipsets)

Now at the end I am sure many of you out there would be disappointed and even disagree or even claim that this is a lie but I am sorry to say it is the TRUTH.
If you wish you go through the whole process that I went through you can. The purpose of this article was to end the chapter of PCIe compatibility question once and for all.
I hope most of the controversies and question regarding this whole 'PCIe compatibility' issue has been solved.
If you further have any doubts please leave your question in comments below.

UPDATE: (After reading the comments I went back to researching again over this question and I must partly decline my statement of the PCIe configuration not being backward compatible. They in fact are very much compatible after a motherboard update (In some cases even the update wasn't needed. Sorry for the misguided information but I tried my best of reaching to the root of this controversy and reached a partially mistaken conclusion. So once again guys, if your graphic card doesn't work on your old motherboard then an UPDATE from from motherboard manufacturer will most likely solve your problem. My sincere apologies for any inconvenience or confusion caused. Thank you for all sharing your helpful experiences, as my final aim was to help ease the confusion and frustration that is involved with building a PC for the 1st time. Cheers to PC gaming!)

Comments (22)

wow!! thanks for all the in depth information .. I was considering getting an hd7750 for my old mobo which only has pciex16 v1.1 slot. now that you have cleared the air of confusion that hd7000 series card will NOT WORK on pcie 1.1 you definitely saved me the trouble. but just wanna ask if the hd5000 and hd6000 series cards will work fine on pcie 1.1?
wow!! thanks for all the in depth information .. I was considering getting an hd7750 for my old mobo which only has pciex16 v1.1 slot. now that you have cleared the air of confusion that hd7000 series card will NOT WORK on pcie 1.1 you definitely saved me the trouble. but just wanna ask if the hd5000 and hd6000 series cards will work fine on pcie 1.1?
HD 6000 series uses PCIe x16 2.1 slot which again has a similar interface to PCIe x16 3.0 but just the bandwidth of PCIe 2.0. So I doubt that would work. But as I have personally not tested a PCIe 2.1 card I cannot tell you that for sure. You can still find some Sapphire HD 6870's that use PCIe x16 v2.0 and that would work with you for sure.
Still to confirm things once more you should try contacting sapphire. They are very helpful and would anwer you right away.
I dont know much about HD 5000 series but if they use PCIe 2.0 then you are good to go.
The lower end 600 series cards are PCIe 2.0 thats why it worked, not until i think either 650 or 660 its PCIe 3.0 again
The card I tested was PCIe 3.0 version itself. Further Nvidia has claimed that any card from 600 series is fully compatible with older motherboards that have PCIe v1.1
I just got my new GTX 660ti yesterday and if seems to working flawlessly. Maybe the bandwidth of PCIe v1.1 slot is limiting its performance slightly its nothing noticeable.
I used for more than a year a PCIE 2.1 card (HD5700) on a PCIE 1.1 motherboard (Gigabyte G31M-S2L),
Like I said I do not know about PCIe 2.1 since I have not tested it personally nor inquired about it anywhere.
While sources confirm that AMD cards from PCIe 3.0 does not work on PCIe 1.1 I am neither a engineer nor a have any formal education in Computer components. I'm just an enthusiast in computers and gaming like most of you all and whatever info i had regarding them I have mentioned in my article.
"Most of us would agree when I say that Nvidia cards like GTX 600 series use much more power than the HD 7000 series."

Actually I don't think most of us would agree with that statement. If anything the Nvidia GTX 600 series has shown to be more power efficient than AMD's Radeon 7000 series. And all Nvidia's GTX 600 series released so far have been PCIe 3.0. Anyway what I find interesting is there is little difference performance wise between different PCIe versions. The only time more PCIe bandwidth is really beneficial is in multi GPU setups. Now compute performance that is a different story.
This week I installed an Afox HD7850 2Gb low profile card in an Acer Veriton S661 that has the Q35 chipset, PCI-e 1.1 x16.
Card works like a dream....
Well the twist is this statement "but most motherboards with PCI Express 1.1 connectors are provided with a BIOS update by their manufacturers through utilities to support backward compatibility of cards with PCIe 2.1" from wikipedia...
http://en.wikipedia.org/wiki/PCI_Express#PCI_Express_2.1
I've checked my BIOS update history (Intel DG33FB) http://downloadmirror.intel.com/17930/eng/DP_0572_ReleaseNotes2.pdf and indeed found they've provided an update for the additional power requirement of PCI E 2.1 adapters (see BIOS update version 0572)
So my guess is in general the nVidia card will fit onto any PCI Express x16 slot, and the Radeon will go down to as below as PCI E 1.1 provided it had a BIOS update from the manufacturer to facilitate the greater power requirement of the PCI E 2.1 and above cards...

@Nian I've checked all Intel motherboards with Q35 chipset is provided with an update to handle updated PCI E adapters. If you've a BIOS after July 2009 you most likely have the updated BIOS !
I have to disagree slightly with this article about the Radeon HD 7770, I to had the same fear but after doing some research decided to just recently pull the trigger, I purchased a gigabyte factory OC'd HD 7770 1GB card for my older LG775 based system with PCI 1.1, I was replacing a Geforce 8600GT. After removing the 8600 drivers completely I shut down and installed the 7770, system booted fine. I installed the latest catalyst drivers and everything works great. The only drawback is that the 1.1 slot is a bottleneck for the video card hindering performance by about 20%, but hey with the Geforce my Winows 7 Index score was 6.3, with the HD 7770 it is now 7.5. My 3DMark score went from just over 1000 for graphics to 3850. So it works fine for me with my 1.1 slot. I have no idea either if my bios has the latest firmware or not as I have neglected to look into this for quite a while now
Thank you for posting such great information.
It was cool to read that NVIDIA rules the reverse compatibility with PCIe v1.1.
Below my configuration :
MB ASUS P5G41T-M LE - Chipset Intel G41 / ICH7 |
I just purchased : ASUS NVIDIA GeForce GTX 650 Ti | 1Go GDDR5 - 928/5400 Mhz - PCI Express 3.0 - HDMI/DUAL DVI/VGA
to replace my old Geforce 8800GTX 768 MB DDR3 OC - MSI

it works 100%
Thank you for posting this vital info! I was on the verge of making a major mistake. Looking at specs for an HD 7790 I found a note saying it only supported down to v2.0. I was sure the were all backward compatible, having been told this many time in the past. But now I realize that the last time I was told this, was about a Nvidia card.

Guess Nvidia just made 1 more sale, just don't know what card yet. No reason to upgrade the rest of my hardware, just replacing a 8800GT not functioning properly.

I can confirm that the (ASUS) GTX 760 is compatibile with PCI e 1.1 and in particular the G31 chipset.

Backstory: My old gpu died (HD 4850) after 4 years of use. Replacing it meant using a PCI e 3.0 card on my very old ASUS P5KPL AM SE motherboard. After days of surfing the net, sending e-mails to almost every possible seller of gpus (ASUS, Gigabyte, MSI, Zotac, Gainward, Palit, Sapphire) I found this thread that completely shattered my hopes... Anyway, I decided to go with it as the alternative was Intel GMA 3100 graphics that lag even when playing video... Long story short, I got the card, installed it and... black screen!! After a short heart attack (I joke of course), I decided to plug the DVI cable in a different DVI port (the DVI-I port) and ... MAGIC! The card works fine, but will have to try some newer games to see just how much my Core Quad 8400 bottlenecks the 760. Thank you very much for this thread and all the comments. I couldn't be happier
Update: Max GPU usage is 90%. Very small bottleneck if you ask me....
And exactly half a year later, I find this thread and proceed to shoot at least one hole in the theory that a PCI-Express 1.1 slot is necessarily incompatible with a PCI-Express 3.0 card.

I have a Dell Vostro 200 with a Foxconn G33M02 (G33 chipset) with a Sapphire (yeah, them of all brands, ironic huh?) AMD Radeon HD7770 1GHz Edition. I'm posting with it now. In fact, the card has been in there since August. I'm running two 20" widescreen monitors off of it.

Please be so kind as to explain to me how it DOESN'T work? This oughta be good.

Now as far as bottlenecked, yes, absolutely, I'm sure it is. It's only an E7400 (was an E6550 until I got a faster chip from eBay). I've run AMD System Monitor on it on the second monitor while gaming and rarely see much more than 50-60% GPU utilization. But I'm also only running at 1680x1050. Still, given that the GPU isn't really stressed, it just allows you to turn up the AA and shaders and whatever it can do that has nothing to do with bus or CPU bottlenecks. But I know that HD7770 isn't being properly fed. It'd take probably a Core i5 or FX 6-core to keep it busy. Maybe I overbought on the GPU, but I'd rather have a rig imbalanced GPU heavy than the other way around.

Maybe if I BSEL mod the E7400 to 3.5GHz (if the chip can take it) that'll help? Or is PCI-E 1.1 a bottleneck? I've read that 2.0 vs 3.0 makes an unmeasurable difference in practice.
I have an hd 7870 on a pci-e 1.1 x16 slot. the card runs fine with my fx-6300. I have it on an asrock n68-vgs3 fx board with an ancient NVidia chipset (I bought I board that would work with what I had at the time and allow for some upgradability. I'm getting a decent motherboard soon and giving this one to my dad whom has an old 775 celeron)

Granted I do have some bottlenecks and graphical "glitches" every so rarely, performance in games is very playable at 1080p 30 - 60 fps ( I do keep vsync on ... I get terrible tearing without it)
I got my EVGA Gtx 750 ti Ftw today. My system is not detecting it. No video is displayed when i turn on the system and my LCD GOES TO SLEEP.
Specs are:
Intel E6750 Core 2 duo 2.67 Ghz.
Intel DG33FB MotherBoard.
Cooler Master 460W PSU.
awrrwa, try clearing/resetting your CMOS. I had a similar issue with my asus motherboard not recognizing AMD video cards but seeing Nvidia cards fine.
Overclock.net › Articles › The final answer to the controversial PCIe x16 version compatibility.