There’s been a lot of question marks raised about the PlayStation VR, not least how it manages to provide a supposed high quality experience on a cut price console. Priced at $399 and significantly undercutting the $600 Oculus Rift and $800 HTC Vive, Sony’s been working its own brand of black magic once again.

The reaction to PlayStation VR’s price point has been swift yet unsurprising - Amazon has been reporting almost instant sellouts worldwide, and from the sound of things other stores aren’t faring too badly either. But just what is PSVR and how can the humble PS4 power a 120Hz 1080p display. We spoke to VR expert and VR World Congress organiser Dan Page for the full tech breakdown….

First things first, what sets the PlayStation VR headset apart in technical terms. “There's a lot to talk about here - as it's powered by the PS4 you'd expect a huge compromise in terms of performance compared to the Rift and Vive, but some very clever thinking from Sony has meant this isn't necessarily the case, or at least the consumer won't feel like it is anyway,” explains Page.

“Framerate has always been an important topic in the games industry but the rise of VR has practically, and sometimes quite literally quadrupled our demands of it. While the HTC Vive and Oculus Rift run at 90hz, and the Gear VR at 60hz, the PSVR comes out on top by being capable of displaying at 120hz in three different modes. Why is this important? To put it simply: a higher framerate, when combined with the necessary low latency, is less nausea-inducing than a lower framerate. High-end device manufacturers have effectively set an industry standard at 90hz as an absolute minimum, while the mid-range Gear VR sits at 60hz.”

The modes in which the PSVR displays its frames are as follows:

60hz rendering (by the game/experience) with 120hz display via "asynchronous reprojection." 90hz rendering resulting in a 90hz display 120hz rendering to a 120hz display.

“This means some developers will chase a native 120hz with clever optimisation and/or low-poly graphics, while others will shoot for the are more achievable 60hz by relying on Sony's "asynchronous reprojection", says Page. "Others, however, will go for a native 90hz, the same they'd be aiming for when producing content for the HTC Vive or Oculus Rift, albeit on much more powerful hardware."

As for what asynchronous reprojection even is, Page clarifies “It's what Oculus chooses to refer to as "asynchronous timewarp", and to quote Oculus's Michael Antonov "Asynchronous timewarp (ATW) is a technique that generates intermediate frames in situations when the game can't maintain frame rate, helping to reduce judder. However, ATW is not a silver bullet and has limitations that developers should be aware of.”’

“The PSVR also differs to the Vive and Rift in that its display uses a single horizontal screen which splits the image into two, as opposed to the aforementioned headset manufacturers' choice to go with two vertical screens. This means IPD (Interpupillary distance, the distance between each eye) will be dealt with using a slightly different mechanic to the other headsets - i.e. not by moving the distances of each eye's screen.

In comparison to the other major headsets, Sony opted to go with a significantly lower resolution screen than the HTC Vive and Oculus Rift. You would expect this would mean a bigger issue with screen door effect seen in some headsets (especially older prototypes). Not necessarily. According to Sony’s Dr. Richard Marks: "Not every 1080P is the same. Ours has three subpixels per pixel, so there's a true R, G and B for every pixel; some of the other displays actually don't have the full RGB for every pixel, so they have less subpixels per pixel. The frame rate of PSVR is also very high, but probably the biggest effect is the optics. The designers have done a really good job at matching the optics to the field of view to the screen".

Then there's the external processing unit, which, ever since it first spotted, has been a bit of a mystery. Various sites have rumoured it to be doing all sorts of different things, including serve as an extra GPU, but in fact it does three things to aid PlayStation VR:

It takes the dual stereo image from the PS4 that's going to the headset and converts it to a ratio suitable for the TV meaning those not wearing the PSVR can see what's going on in 2D. It processes the game or experience's "3D audio". It takes the sensor data from the headset and sends it back to the PS4 via USB.

So to clarify then, the external PS VR processor does not provide any additional GPU or CPU horsepower directly to the PS4 whatsoever. It is merely there as a means to convert the image. The PS4 is perfectly capable of outputting at 120 frames per second on its own, but it's up to the developers to scale the visuals down to hit this target.

In terms of whether this technology can be taken and applied to PC, it’s a difficult task. The vast number of different configurations makes optimising for any one a tricky task. The very reason such tricks are employed for PS VR is because the PlayStation 4 lacks the necessary computing power. Compare this to PC where performance can be brute-forced and you begin to see how PS VR and the likes of the Oculus Rift and HTC Vive differ.