Topic: Maximum 7990s per mobo? (Read 5121 times)

I have hit 1330-1340 mh/s using msi afterburner on my sapphire 7990.


100mhz ram, 0% voltage, using guiminer.

If linux or cgminer its probably possible to hit quite a bit higher.  Right now I run 1240-1285 mh/s range  24/7 for weeks.  Temps 79C or below.  3 GPUs.

*note I am only giving results for my 7990 card.

It can probably hit 1376-1400+mh/s...yes I believe its possible.

virtualization not visualization

I said 'normally'. That means under 'normal' circumstances where official, unmodified drivers, OS kernels and BIOS are used.

The AMD Drivers limit you to 8 cores, with means 4x 7990 tops.

In that 18 slot rig RJK was going to build, he was planning on using virtualization to split up the 18 cards into virtual OSs, so the drivers would only handle ~6 at a time. That FASTRA2 computer uses Nvidia, which have different drivers.

You can look all you want, but you won't find anyone with more than 8 AMD GPU chips in one computer.

1. In theory you may be able to connect... maybe as much as 20 GPUs if you find a suitable motherboard with that many PCI-E slots?

Take a time to read:

18 GPUs: https://bitcointalksearch.org/topic/mining-rig-extraordinaire-the-trenton-bpx6806-18-slot-pcie-backplane-pics-64450
13 GPUs (nVidia though): http://fastra2.ua.ac.be/?page_id=214

In short: the more GPUs, the more problems you will run into.

Normally, 8 GPU (or up to 4 dual-GPU graphics cards) is the max. you can get on one motherboard.

Problems that you will encounter are:

- hardware (motherboard) limitations, some have more PCI-E slots than they can simultaneously handle, in order to use them all sometimes you may need to disable some unused features / disconnect some devices on the motherboard.
- software - BIOS
- software - OS
- software - GPU drivers
- obviously you will need to use >1 PSU for each 14 GPU rig so make sure you know how to connect those without frying anything
- profitability - the difficulty will probably increase so much that the investment will not pay for itself (unless we see a rapid increase in BTC price)

2. as for the temperatures:
- use GPU-Z to get the temperatures because it can read from more sensors than most other software
- sometimes the GPU is cool but the VRAM (shouldn't be the case if you underclock it for SHA) or the VRM is runnnig very hot (especially the VRM if you like to overclock and/or increase the voltage)

3. If you hashrate is 500 MH/s check if you are mining on both cores because it should be double of that.

exactly. i think either the users are limited by the temps or just not pushing the cards all the way out.

OC, powertune, intensity, with proper cooling....

I'm building a quad 7990 watercooled rig this week, I'll keep you all posted on performance and temps.

Early testing showed that the thermal paste is crap or applied very badly, temps between the two cores varied wildly and occasionally 20C difference between them.
One card went straight up to 103C on one GPU within a couple of minutes!!!

Thanks Tom_o!!!  Do I still need to use a crossfire for 2 xfx 7990?  Also, just wondering what type of fans are the best to cool down the cards?

Agreed, I am curious on the hashrate.  I've heard people say 1200ish but I wonder if those are unoptimized hashrates without proper settings.

has anyone tried pushing the card to max potential and see the hashing power? shouldnt it be somewhat of around 1400 mhash considering its 2x 7970?

Stock cooling is the cooling already on the card. As for people referring to open case they generally mean taking the side(s) off of the computer case. For dual 7990 you also want a big fan aimed into the general pc case, 500Mhash sounds like they're throttling back due to getting too hot!

They just started dropping very recently.  The 7970s have also recently been on deals for 330-350.  Both Amazon and Newegg.

http://www.newegg.com/Product/Product.aspx?Item=N82E16814202036
http://www.newegg.com/Product/Product.aspx?Item=N82E16814131483

sorry for being such a newbie but what is stock cooling and how do you open the case for a 7990?  I have two xfx 7990 but temps gets to as high as 95 degree C with a hash rate of around 500MH/s.

Can someone please help me with the best configuration to maximize hashing power.....I did pay big $$$ to get them..thanks

Can you share where you have seen 7990 at 900 bucks?

Every few places where I have seen them online and in local stores, it was way above the 999$ MSRP. The price that I have seen varies from 1050 up to 1150$ and if you search very hard online, you will find insane sellers asking for 1400+$ for it.

my 7990 has been mining for at least 1-2 weeks straight...1242mh/s


gpu2@74C  gpu3@78C

Sapphire 7990, stock cooling only. open case now.


I recommend sapphire 7950 or sapphire 7870XT (tahiti not picarin)  for best ROI.

If you plan on selling the 7990s eventually, sure its fine to mine with them and get a few hundred $$ of BTC.

Windows has that 8 GPU limit, but it shouldn't affect linux as far as I know. I would say you can put 7 of them in that case.

Using Linux and a mobo that can handle 7 simultaneous slots like the MSI-Z77A-GD65, how many 7990s could you put on there and get it working?  Using powered risers of course.  I am just wondering if there are any limitations given the dual gpu nature of the cards.

This is theoretical so I don't want to hear any price/gigahash mumbojumbo.  Although now that they can be had for 900 bucks and they only suck 375 watts vs 500 watts on two 7970s, that's not too shabby if one is looking to maximize horsepower, power efficiency, and physical space usage.

So when you look at it that way, for ex;

14 7990s @ 375 = 5250 + 2mobos/cpus = 5650watts @ .12kW/hr = $455 per month/$5460 per year
vs
28 7970s @ 250 = 7000 + 4mobos/cpus = 7800watts @ .12kW/hr = $629 per month/$7548 per year

= $2,088 saved in electricity per year.  Even more if you count the energy saved on psu efficiency loss from having more systems.

$100 premium per 7990*14 = $1400 overspent on video cards - 2 extra mobos/cpus/ram @ $500 = $900 overspent on 7990s which equals 5.17 months and the premium for 7990s is paid off.  Everything after 5 months is more profit because of all the saved electricity.

Plus it's easier to build a medium sized box for 14 cards stuck in the corner of a room and have it ducted intake/exhaust through a window, than a huge box with 28 cards.

Anyway back to the topic at hand.