GPU upgrade: understanding PCIe vs. Thunderbolt

[jcurri]

I have a ton of questions regarding upgrade possibilities with my current GPU. I've done a little bit of research on the thunderbolt to PCIe bridges like the ones offered by Sonnet: http://www.sonnettech.com/product/echoexpressse2.html
I'm not quite clear, however, on the bandwidth offered by PCIe and thunderbolt.

Question 1: Does anyone know what bridges the current video card to the motherboard of a late 2012 iMac, and what the bandwidth of that bridge is?

Question 2: If I wanted to by the above PCI:thunderbolt bridge, would a higher end video card like say, the NVidia GTX 780, max out the bandwidth offered by thunderbolt if I was playing a game like battlefield 4?

Question 3: Is there anywhere online where I could buy a 680MX with 2 GB of dedicated ram (or a similar card that is compatible with the late 2012 iMac) and simply install it myself?

Alternatively, what do you think my chances are of going to an apple store and offering to pay a decent amount of $$ for an upgrade?

Thanks all...

 

[jcurri]

I left out that it's a 27" late 2012...

 

[Krevnik]

Question 1: Does anyone know what bridges the current video card to the motherboard of a late 2012 iMac, and what the bandwidth of that bridge is?

It is PCIe, but I'm not sure how many lanes are wired up, and how much bandwidth of that provided it actually uses. Although graphics cards usually get 8 or 16 lanes. PCIe 2 offers ~4Gbps per lane. Thunderbolt offers 10Gbps per channel and offers two channels.

5 lane PCIe is as fast as dual-channel thunderbolt. And graphics cards use more lanes than that. (This does ignore 3.0 which makes PCIe double the speed of 2.x, but is just starting to appear)

Question 2: If I wanted to by the above PCI:thunderbolt bridge, would a higher end video card like say, the NVidia GTX 780, max out the bandwidth offered by thunderbolt if I was playing a game like battlefield 4?

Going by the numbers above, very likely. I am not sure a GPU over thunderbolt will get to use both channels, but even then it is basically bandwidth starved compared to how it was designed to operate. And running out of VRAM becomes expensive due to added latency to swap textures from RAM over thunderbolt.

Question 3: Is there anywhere online where I could buy a 680MX with 2 GB of dedicated ram (or a similar card that is compatible with the late 2012 iMac) and simply install it myself?

Nope, the GPU is soldered on the logic board with the 2012. You'd need a whole new logic board salvaged from the model that has the GPU you want.

Alternatively, what do you think my chances are of going to an apple store and offering to pay a decent amount of $$ for an upgrade?

The odds are pretty terrible. Apple doesn't offer such a service.

 

[leman]

I'm not quite clear, however, on the bandwidth offered by PCIe and thunderbolt.

It is quite clear actually. TB is a wrapper around 4x PCI-E 2.0. This makes TB equivalent of a 2x PCI-E 3.0 link. Current high-end GPUs are usually connected via 16x PCI-E 3.0.

Question 1: Does anyone know what bridges the current video card to the motherboard of a late 2012 iMac, and what the bandwidth of that bridge is?

Well, its soldered on the mainboard. The interface is either 8x or 16x PCI-E 3.0 (most likely 8x though) My iMac is at home so I can't look right now, but its possible that the interface can be seen in the system profiler.

Question 2: If I wanted to by the above PCI:thunderbolt bridge, would a higher end video card like say, the NVidia GTX 780, max out the bandwidth offered by thunderbolt if I was playing a game like battlefield 4?

You can see the impact of available bandwidth on gaming performance here: http://www.anandtech.com/show/5458/the-radeon-hd-7970-reprise-pcie-bandwidth-overclocking-and-msaa

Basically, the difference between 8x and 16x is virtually non-existent while 2x does exhibit performance degradation. Modern games tend to be shader/fill limited though - in other words, actual rendering takes lots of time, so the speed at which data is supplied to the GPU plays a less significant role.

TL;DR: while the 2x PCI will certainly hinder the GTX 780 from reaching its full potential you will still be able to pretty much max everything and get very decent framerate.

Question 3: Is there anywhere online where I could buy a 680MX with 2 GB of dedicated ram (or a similar card that is compatible with the late 2012 iMac) and simply install it myself?

No. Its soldered.

Alternatively, what do you think my chances are of going to an apple store and offering to pay a decent amount of $$ for an upgrade?

0%

 

[X-Ravin]

Sorry to hijack a little, but would the external GPUs be able to use the iMac's screen? I know someone figured out a trick to get a Mac laptop to use an external GPU for the internal screen, but I don't know if it would work for iMacs.

 

[MatthewAMEL]

http://www.bit-tech.net/news/hardware/2013/06/06/silverstone-external-graphics-card-case-deb/

 

[Mac32]

External high end GPU for gaming = poor performance

End off story. I saw benchmarks for thunderbolt 1 with a GTX680, and it lost up to about 40% performance in real life. Obviously the performance loss would be even greater with GTX780 or similar cards. We have yet to see benchmarks for thunderbolt 2, but I'm very sceptical.. I'm seeing some people promising great results with external thunderbolt GPUs, but they are failing to deliver the proof.

Sorry, just trying to keep it real.

 

[yjchua95]

External high end GPU for gaming = poor performance

End off story. I saw benchmarks for thunderbolt 1 with a GTX680, and it lost up to about 40% performance in real life. Obviously the performance loss would be even greater with GTX780 or similar cards. We have yet to see benchmarks for thunderbolt 2, but I'm very sceptical.. I'm seeing some people promising great results with external thunderbolt GPUs, but they are failing to deliver the proof.

Sorry, just trying to keep it real.

Proof's here mate: http://forum.techinferno.com/diy-e-...1-macbook-air-gtx570@x2-2-win7-bios-th05.html

Note that it's just Boot Camp. Good enough for most purposes. But you do have a point. That PCIe-Thunderbolt adapter will limit the link just to 5 Gbps. So no point getting a GTX Titan. Just stick with the GTX 5xx-6xx series if you intend to wire up an eGPU via Thunderbolt.

 

[Mac32]

Proof's here mate: http://forum.techinferno.com/diy-e-...1-macbook-air-gtx570@x2-2-win7-bios-th05.html

Note that it's just Boot Camp. Good enough for most purposes. But you do have a point. That PCIe-Thunderbolt adapter will limit the link just to 5 Gbps. So no point getting a GTX Titan. Just stick with the GTX 5xx-6xx series if you intend to wire up an eGPU via Thunderbolt.

?? I don't see any benchmarks. I know it can be done practically, but the performance just isn't good enough to warrent the expense when compared to other solutions. You would not be able to improve on the performance of ...say a 680MX, at least not with thunderbolt 1.
Believe me I had great hopes for this myself, but then I saw the benchmarks..not so good.

 

[yjchua95]

?? I don't see any benchmarks. I know it can be done practically, but the performance just isn't good enough to warrent the expense when compared to other solutions. You would not be able to improve on the performance of ...say a 680MX, at least not with thunderbolt 1.
Believe me I had great hopes for this myself, but then I saw the benchmarks..not so good.

My bad. But at least the video's enough of a testament that a PCIe-Thunderbolt based eGPU is the next best thing to having a discrete one. It's fast enough to play games at high settings.

 

[jblagden]

Proof's here mate: http://forum.techinferno.com/diy-e-gpu-projects/3960-[guide]-2013-11-macbook-air-gtx570@x2-2-win7-bios-th05.html

Note that it's just Boot Camp. Good enough for most purposes. But you do have a point. That PCIe-Thunderbolt adapter will limit the link just to 5 Gbps. So no point getting a GTX Titan. Just stick with the GTX 5xx-6xx series if you intend to wire up an eGPU via Thunderbolt.

How does it limit the link to 5 gigabits per second? It’s a 4 lane PCIe slot, which has 20 gigabits of total throughput. Or are you talking about the per-lane bandwidth?

 

[jblagden]

I’ve recently learned that a Thunderbolt eGPU can’t use a MacBook’s internal screen in OS X. Could this problem be circumvented by using this headless video accelerator: http://eshop.macsales.com/item/NewerTech/ADP4KHEAD/

 

[desmond2046]

I have a ton of questions regarding upgrade possibilities with my current GPU. I've done a little bit of research on the thunderbolt to PCIe bridges like the ones offered by Sonnet: http://www.sonnettech.com/product/echoexpressse2.html
I'm not quite clear, however, on the bandwidth offered by PCIe and thunderbolt.

Question 1: Does anyone know what bridges the current video card to the motherboard of a late 2012 iMac, and what the bandwidth of that bridge is?

Question 2: If I wanted to by the above PCI:thunderbolt bridge, would a higher end video card like say, the NVidia GTX 780, max out the bandwidth offered by thunderbolt if I was playing a game like battlefield 4?

Question 3: Is there anywhere online where I could buy a 680MX with 2 GB of dedicated ram (or a similar card that is compatible with the late 2012 iMac) and simply install it myself?

Alternatively, what do you think my chances are of going to an apple store and offering to pay a decent amount of $$ for an upgrade?

Thanks all...

Don't buy an external graphic card (~$400) if you just want to improve the gaming performance. It is a complete waste of money. You can use that money to
1. Buy a PS4.
or
2. Build a PC with maybe Athlon 860K ($70), 2nd hand Radeon 7970 ($130), MB RAM SSD Case etc. ($250)

 

[Samuelsan2001]

Don't buy an external graphic card (~$400) if you just want to improve the gaming performance. It is a complete waste of money. You can use that money to
1. Buy a PS4.
or
2. Build a PC with maybe Athlon 860K ($70), 2nd hand Radeon 7970 ($130), MB RAM SSD Case etc. ($250)

And you'd need a PCIe enclosure for that graphics card which is another $400, at which point you could just buy a good gaming rig.

 

[jblagden]

Don't buy an external graphic card (~$400) if you just want to improve the gaming performance. It is a complete waste of money. You can use that money to
1. Buy a PS4.
or
2. Build a PC with maybe Athlon 860K ($70), 2nd hand Radeon 7970 ($130), MB RAM SSD Case etc. ($250)

I’ve considered those options the past, but I don’t really care for consoles(I prefer I mouse and keyboard), I don’t want to run Windows, I don’t want a Hackintosh and I don’t want another computer(i just want to stick with one computer). For me, an eGPU is the best option.

 

[old-wiz]

I’ve recently learned that a Thunderbolt eGPU can’t use a MacBook’s internal screen in OS X. Could this problem be circumvented by using this headless video accelerator: http://eshop.macsales.com/item/NewerTech/ADP4KHEAD/

The linked part is for a Mac Mini. The external GPUs have no access to the laptop screen.
It is really easier to just buy a PS/4 or Xbox and a monitor if you are really into gaming.