It's easier to carry around your computation than it is to beam it at your skull.
Computex 2016, held in Taipei recently, was a fascinating show for VR watchers, with some major trends in PC-based VR coming into focus. One of those is the VR backpack — effectively a battery-powered PC in a rucksack that connects to your headset like a desktop tower. The only difference is instead of tripping over wires you've got this thing attached to your back.
Zotak, MSI and HP all showcased this new type of VR wearable at Computex. All three were variations on the same concept: HP and MSI went for a hard plastic shell, making for a heavier device, while MSI's was more rucksack-like and lightweight — around three pounds.
Backpack PCs look silly. But then nobody looks cool wearing VR.
Let's address the ridicule factor right away. Yes, a backpack-based PC is yet another way to look silly while inside virtual reality. (Alongside #vrface and messed up hair.) But there's a reason why these things are part of a trend and not just a quirky one-off. For as dumb as they may look, they actually represent an elegant solution to room-scale VR's biggest problem.
If there's one thing that can really kill the immersion of an HTC Vive session, it's that umbilical wire tethering you back to your PC. So why not just develop a wireless headset? Well, the problem is the sheer amount of data that needs to be transferred between the PC and the headset, not to mention the lightning-fast latency requirements of a nausea-free VR experience.
Beaming microwaves at your head is probably a bad idea.
We raised this point with Valve's Chet Faliszek at Mobile World Congress earlier this year, and he suggested that currently the only way to do it would be to beam microwaves at the headset. Given that the headset also contains your head, that's probably a bad idea.
You're looking at two high-res viewports at 90Hz, in addition to all the sensor data from the headset. And as the resolution and fidelity of VR displays increases in the coming years, that bandwidth requirement is only going to increase. For the foreseeable future, PC-based VR is going to need wires.
That being the case, mobilizing the PC driving the experience actually start to look like the smart thing to do. Portable PCs are nothing new, and while lugging a ten-pound plastic behemoth on your back might be even more distracting than that umbilical wire. But Zotak's VR backpack, which includes an Intel Core i5-6400 processor and an NVIDIA GTX 980 graphics card, weighs little more than a laptop inside a rucksack. Maybe you'd feel the weight more after a couple of hours, but for the few minutes we tried it, it wasn't especially burdensome.
Yet another VR thing you need to charge.
And that brings us to another trade-off: If all this stuff has to be mobile, it's got to be battery-powered, and that puts an artificial limit on your VR playtime. Right now the 60,000mAh cell powering Zotak's kit gets you two hours in VR. (That's half the lifespan of the HTC Vive's controllers, which are designed to go for four hours between charges.)
There's also the economical issue of buying a whole separate PC inside a bag just for VR. But hey, no tripping over wires!
So you're trading one set of problems for another. However Moore's law being what it is, the challenge of putting more computing power into a smaller space — and making it run for longer on the same power source — will get easier with each passing hardware generation. (It's certainly an easier path of technological progress than working out how to wirelessly connect an HMD without frying your brain.)
We're still working out the best way to do truly immersive, room-scale VR. All the options on the table right now are expensive and, from the outside, slightly ridiculous. But we think VR-centric backpack PCs — wild as they might seem at the moment — are here to stay.