External GPUs

Many have pondered this question and few have come up with an answer. In this article, we will discuss just how far we are from obtaining an external solution for laptops. What if it could be powerful enough to play some of today’s demanding games such as Crysis, Unreal 3 engine based games, and more? Gaming on a laptop is still an uncommon task, and without the ability to build your own, prices on such laptops can be ridiculous. In addition, any laptop that comes with a decent graphics card are usually sized between 15 to 17 inches. This makes for limited portability.

What if an ergonomically sized high end external graphics card were used? Possibly this external solution could be used on the go, or at the very least convenient to lug around. In addition, we will analyze just how much today’s cards may require in terms of bandwidth. Do they even need PCI-E 1.0 or 2.0? Let’s find out.

USB 2.0, USB 3.0, eSATA, Express Card Interface

USB 2.0 came out in 2000 and was specified to handle 480Mb/s, that’s mega bits per second. Dividing by eight this translates to 60MB/s, which is Mega Bytes per second.

USB 3.0 will be released in late 2009 or 2010. It is specified to handle 5000Mb/s or 5Gb/s. This translates to 625MB/s; rounding off, that comes to about 10.42 times more bandwidth over USB 2.0.

eSATA has 300MB/s and seems to be an interesting alternative to USB 2.0. But, is 300MB/s enough?

The Express Card Interface only has 250MB/s and already has the ASUS’ XG Station working on it. Is the XG station the solution? What are its limitations? Fist off, it is bulky, meaning that a fully speced out desktop counterpart was used. However, in today’s world it is possible to invision a slimmer device, one which could use a mobile counterpart. Either way, laptop portability would be severely hindered by the XG Station. What makes matters worse is the fact that, in its current state, it requires another monitor. So, to be more practical the external solution would need to use the attached display bundled with the laptop.

Putting it all together

So, what bandwidth does a modern day high end GPU use? According to a multitude of benchmarks done by Tomshardware.com, an x1900XTX need at least 4 lanes off of the PCI-E 1.0 spec. That is 250MB/s per lane (PCI-E 2.0 is 500MB/s per lane and PCI-E 3.0 is 1000MB/s per lane). So, 4x250MB/s comes out to 1000MB/s or 1GB/s. A G80 8800GTS need closer to 8x, that means an 8800GTS requires about 8 lanes (2GB/s) to perform closer to what we would expect. Now you could imagine that an 8800GTX and above would require 8 lanes or more, which again, is 2GB/s and above.

Now, AGP 8x supports approximately 2.1GB/s. So, an 8800GTX may or may not work, but it comes close. As we can see, the extra bandwidth that PCI-E 1.0, 2.0 and eventually 3.0 provides can come in handy with today’s newer cards.

According to the Toms Hardware article a high end DX9 card from the X1900 series or possibly the 7 series (7900GTX and above) would require closer to 1GB/s, else you would have to sacrifice performance due to the limited bandwidth. The XG station uses a 7900GS, but recent news has indicated that it comes paired with an 8600GT instead. However, the 7900GS is not considered a high end DX9 card, so I can see how, if under clocked, one may be able to get away with a 250MB/s bandwidth cap.


Just how far are we from external high end portably graphics cards? Well, let’s recap. USB 2.0 supports 60MB/s and USB 3.0 supports 625MB/s. A high end DX9 GPU requires close to 1GB/s. A card like a GTX 280 would require closer to 3 to 4GB/s. Reading this, we can immediately throw out USB 2.0, eSATA, and the express card interface out the door. That means in order to have a high end gaming experience we would need at the very least AGP 8x’s bandwidth, which is 2.1GB/s. So, 2.1GB/s divided by USB 3.0’s 625MB/s come out to about 3.36.

Ouch, that means it would take at the very least 3 to 4 USB 3.0 slots to match the bandwidth of AGP 8x. Now that’s not too bad, but think about the fact that USB 3.0 isn’t even out yet. Think about how newer DX11 GPUs come out this fall, and how much bandwidth they may require? Can USB technology even keep pace? At the current rate, ten times the bandwidth per 10 years, then I don’t think a USB external GPU solution would do the trick.

What about newer technologies besides USB 3.0? Well, we may never see an external card, since cloud computing could a viable alternative. Also, Nvidia is pushing for better integrated solutions. The 9400m may not be the best, but it’s a good start. It is very likely that laptops themselves will just be ultra potable graphics powerhouses when compared to today’s standards. In addition, a newer eSATA port may also do the trick. However, the SATA 6.0 spec isn’t enough, since 6Gb/s (gigabits per second) comes out to 750MB/s.

What needs to be done is emphasize the MXM PCI-E standard for laptops. The MXM slot already has an x16 PCI-e slot. Having external access to the slot would clearly make it possible for external cards to get the bandwidth they need. Unfortunately, Intel is keeps pushing their integrated GPUs into laptops. Even though Intel’s Larrabee may be a step in the right direction, its performance and use in laptops has yet to be seen.

Laptops with an express card slot can take advantage of the MSI external GPU solution.

MSI external GPU solution

However, this solution does require a wall outlet. So, this is not quite what I envisioned. What I originally envisioned was a completely mobile GPU that doesn’t require a power brick. Unfortunately, batteries do not have the capacities we need in order to power such a mobile solution. The completely mobile plug and play GPU is still a bit off.

Ultimately, PCI express x16 is the sweet spot, even hard drives will abandon SATA in favor of PCI express in the future. PCI Express 1.0 and 2.0 provide enough bandwidth for just about everything, and unfortunately so far it is the only viable solution for any type of hardware craving the extra bandwidth. Thus, we should now have a greater understanding what we may expect in the future and what are our limitations today for external graphics card solutions.

-How far away are we from external video solutions for laptops?