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External graphics card in thunderbolt

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February 27, 2012 1:11:33 PM

I have a 2011 MBP ( Quad core i7 @2.2ghz , 8gb ram ddr3, 500 GB @7200rpm and an awful 6750m with 1gb) and i recently saw that there was going to be released an external GPU case for thunderbolt (wich has 10gb/s) www.theverge.com/2012/1/10/2698168/msi-GUS-II-external-thunderbolt-gpu-enclosure

The problem with this case is that it only supports GPU that use 150W or less, and no modern mid-high end gpu ( and im being nice with the high end term here) uses only 150w, so i googled around and found this

http://www.techradar.com/news/computing-components/graphics-cards/how-to-make-an-external-laptop-graphics-adaptor-915616

and this www.hwtools.net/adapter/TH03.html

so, the question is, would it be viable to make this work with a 570gtx for example? if yes would the gtx's performance suffer from the fact it is using that connection?

Thanks in advance for all the answers!
February 27, 2012 2:30:43 PM

ups, i messed up the links.. i'm sorry, i know that one only supports 150w.. but i found a DIY guide, and i was wondering if that would work, as it uses an external PSU ( PS: the links are fixed now)
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a c 125 U Graphics card
February 27, 2012 2:48:10 PM

You could probably mod the power input, but who knows. I'd wait for it to release and some electrical engineers to get their fingers on it and make a DIY (you said you found one... could you link it?)

Anyway, there's quite a few good 150W GPUs out there if you go AMD. They tend to have better performance per watt. A 5850 was 150W TDP, I think the 6870 is lower. When the 7850/7870 come out I'd bet they'll be close to 150W as well and pack a huge punch.

As for speed, PCIe 2.0 is up to 500mb/s per lane, and GPUs connect to 16 lane connectors, which is only 8GB/s. Even at 8 lanes (like in crossfire/SLI) you lose almost no performance.
February 27, 2012 3:03:28 PM

Wow... i must be doing something seriously wrong :??:  no one until now understood what i wanted :D  So i'll try to explain again (sorry English is not my main language):

I found the case shown above, which can only provide 150W and i was quite disappointed, but then, after some googling i found this guide :

http://www.techradar.com/news/computing-components/graphics-cards/how-to-make-an-external-laptop-graphics-adaptor-915616

It explains how to connect an external GPU to your laptop using an (?) Expresscard (not sure if it is that), but has macbook pro's dont have that slot, i could use an adapter to thunderbolt.

http://www.hwtools.net/adapter/TH03.html

Would the second solution work? ( the pci adapter + thunderbolt adapter)

Hope you understand it now.
a c 125 U Graphics card
February 27, 2012 5:07:13 PM

Ohhh, ok. I see now.

In theory, yes it should work. I don't think a PCIe 2.0 16x to 1x adapter is going to give you a heck of a lot of bandwidth though, so you won't want to use a very powerful card.

What's your motivation to do all this?
February 27, 2012 5:13:35 PM

well, the thing is a Pcie 2.0 16x is about 8gb/s and thunderbolt is 10gb/s so in theory it should work without any loss of bandwidth, or am i wrong somewhere?

Motivation? well, i game alot and my mbp's GPU just can't handle the most recent games with the eye candy i want it to have, when im running most games, my GPU is always working at 100% while my cpu never goes above 20%, only on some rare occasions, so it is definitely a GPU problem which would be solved by this external GPU.
a c 125 U Graphics card
February 27, 2012 6:10:58 PM

Well, yes, it is a GPU bottleneck. I guess you run bootcamp? Macs are very overpriced for the hardware you end up with, this $1000 laptop has a 6850m: http://www.newegg.ca/Product/Product.aspx?Item=N82E1683...

But anyway, you have what you have... the reason I think there will be a bottleneck is that card converts the PCIe 16 slot into a 1x slot, which can adapt into the thunderbolt reader thing. There's no way to make 1 lane run as fast as 16 lanes.

In theory there should be a way to simply replace your current GPU, but of course either Apple will charge you an arm and a leg, or else you will void your warranty.
February 27, 2012 6:18:52 PM

humm, well i see, i like macs for some reasons which are off-topic ( cause i hate the GPU's they use...) back on-topic, i see your point with the adapter, i'll look into it near the supplier in my area, Thanks for all the help!

and yeah, thinking about changing anything else than RAM and the HDD in a mac is madness, Its all attached to the Mobo by alluminium or some other metal i can't recall.

Again, thanks for the help!
a c 125 U Graphics card
February 27, 2012 6:29:03 PM

The interesting thing about that adapter card (the PCIe 16 one) is that it seems to have 4 USB outputs for the full bandwidth. It would be really awesome if you could connect the 4 USBs into a thunderbolt cable! Or even go directly to a USB 3.0 hub (or 2.0) as that has a lot more bandwidth than a single PCIe lane. The question is whether the laptop will even recognize that there is an external GPU there.
a c 109 U Graphics card
February 27, 2012 9:31:23 PM

Then there are drivers...
February 28, 2012 4:51:15 PM

Wolfram23, i finally understood what you meant by 16x to 1x (i handt read that part, hehe), i know it is possible to chain thunderbolt devices (screens, SSD's, etc) if it was possible to chain 4 adapters, theoretically would the GPU have at least something like 80~90% of it's normal performance?

About drivers and windows seeing the card, i read on allot of forums that windows 7 automatically handles the drivers, etc etc, It thinks of it has an internal GPU... That is even said in the original article i posted!
a c 125 U Graphics card
February 28, 2012 5:30:06 PM

I'm really not qualified to say whether chaining the adapters together would work like that. Sorry. In theory, it should work.
February 28, 2012 5:46:47 PM

ok, Thanks for the help! Well, i have another question, is the bandwidth used by each card +/- the same? or does a GTX 580 use much more than a GTX 460 for example? I know their speeds can't even compete, but how much does that impact bandwidth?
a c 125 U Graphics card
February 28, 2012 6:08:57 PM

The speed of a card is related to bandwidth, yes. The card needs to receive enough info from the CPU to know what to render, so a fast card could end up choked without enough bandwidth.

The last test I saw, a 5870 lost something like 2-3% of it's performance on average going from 16 lanes to 8 lanes, so basically it's not a lot. Something like a 6990 or 7970 or GTX 590 would lose more dropping down to 8 lanes. On the other hand, a 560 or a 6850 probably wouldn't see a difference at 8 lanes.
February 28, 2012 6:43:37 PM

well, but a 7950 or equivalent would still be much better than a GTX 560 ti for example, even with the loss of speed right?
a c 109 U Graphics card
February 28, 2012 7:00:58 PM

Well I like the idea on gaming with an amd ultrathin laptop and this,,.
a c 125 U Graphics card
February 28, 2012 8:45:06 PM

captainvera said:
well, but a 7950 or equivalent would still be much better than a GTX 560 ti for example, even with the loss of speed right?


Um... not necessarily. But probably. Honestly I haven't seen any tests to less than 4 lanes. Like this one:

August 5, 2012 12:47:10 PM

captainvera said:
Wolfram23, i finally understood what you meant by 16x to 1x (i handt read that part, hehe), i know it is possible to chain thunderbolt devices (screens, SSD's, etc) if it was possible to chain 4 adapters, theoretically would the GPU have at least something like 80~90% of it's normal performance?


Sorry, but chaining does not increase bandwidth. In fact, it reduces bandwidth per card, since they all have to share the same PCIe x1 link. Bottom line -> a laptop PCI-Express card maxes out at about 250 megabytes/second vs up to 12GB/sec for PCIe 2.0, and all attached devices much share this bandwidth. (You'd do 4x better rigging it to work with your FW800 port. :)  That's the beauty of Thunderbolt - although you need a new computer to get the benefits, it finally makes desktop level expandability possible, at least for a small number of devices.

HOWEVER, consider that this is only about transferring data between CPU and GPU - so it depends how the game was written. In principle, if you have a GPU with a lot of memory, and a game that uploads all the graphics once instead of per-frame, you won't need that much CPU to GPU bandwidth.
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