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The Eulogy for Slot-in VR

At Facebook’s Oculus Connect 6 VR developer’s conference the company’s technical leader John Carmack gave a talk about Gear VR and the failings of slot-in VR. While I agree with many of his assertions about Gear VR and slot-in VR, he only touched on a few issues that slot-in VR had that ultimately doomed the technology before it ever had a chance of taking off. I personally used nearly every version of the Gear VR and Google Daydream, so I am very familiar with the pitfalls of the technology and why standalone VR seemed like the correct solution years ago.

Smartphone Thermals

Fundamentally, smartphones are poorly designed for VR.

Yes, they can pretty much do anything for 5 minutes without any issues, but short 5-minute VR experiences are not enough to support an entire industry and thus, longer experiences are needed. The problem is that slot-in VR is fundamentally limited to no more than about 30 minutes of usage, which is when most headsets will start to throttle the device or warn that performance is no longer acceptable for VR. With each generation of slot-in VR, they got closer and closer to 30 minutes of continuous usage, but I assume that’s probably possible with something like a Note9 having more surface area to dissipate heat and a more power efficient system on a chip. Speaking of the SoC, one of the biggest problems that smartphones had for VR is that nearly all smartphones and their thermal designs are specifically designed for bursty workloads, not sustained ones. Over time, SoCs and the GPUs in them from Qualcomm and ARM got better at sustained workloads, but that was never a stated goal until VR happened. Even so, running the SoC at full bore for 30 minutes heated up the device significantly and that paired with having the display at nearly full brightness and running 100% of the time resulted in some very poor thermals. Having the SoC so close to the display because of the tightness of a smartphone design only made thermals worse because both components got hot and heated up one another. Only recently have we seen devices like these gaming phones with improved cooling and active cooling, but even so, gaming is going to give the device better cooling because it isn’t locked inside of a VR headset without much airflow.

Ease of Use

There were some good things about slot-in VR, for example with Daydream, you could simply open up the headset and place your phone inside and close it up and the headset would recognize the phone and vice versa and it would work relatively reliably. However, carrying around a headset with you everywhere that you took your phone was problematic and standalone does not solve this problem, but it also improves the experience even more by adding 6DoF and two controllers, so it is almost an entirely different class of experience. There were also compatibility issues between versions of Gear VR and which smartphones fit in which and their USB connectors. This was less of an issue for Daydream and more of an issue for Gear VR, but at a certain point even Daydream looked silly with some larger sized phones. Audio quality also suffered as phone speakers weren’t a great sounding solution and using headphones adds complexity. Dust was also an issue for me because every time you opened the headset to put the phone in, you introduced more dust and I found bits of dust to be very distracting in darker scenes with small bright light sources like text. Another killer problem that slot-in smartphone VR had was the ‘case’ issue, which is that smartphones are very fragile devices so most people have their phones in cases and most VR headsets weren’t designed to accommodate. That means taking your phone out of its case, which in some cases results in dropping your phone as you remove it from the case and try to transfer it into the VR headset.


While I expect that lots of content from slot-in VR headsets will waterfall into standalone headsets like the Go and Quest, there’s no denying that the 3DoF nature of the Gear VR limited what kind of content could be viewed optimally. The best content for these headsets would be 3D 180 or 360 content, which has struggled to take off. I have seen some amazing 360 and 180 content as well as 3D 180 content, but the reality is that there aren’t enough headsets out there yet to entice content creators to aggressively pursue the format. As such, many of the standalone headsets had limited content experiences, partially limited by what kinds of controllers they utilized. The Gear VR and Daydream headsets both had coarse 3DoF controllers, which were great for navigating menus, but not necessarily great for gaming or social interactions. Having Google and Facebook segment the markets with their own content ecosystems didn’t help the situation either, but now Daydream appears as good as dead and mobile VR developers are mostly focused on Quest.

Never Meant to Be

I think I realized slot-in smartphone VR was dead around the time the second generation of Google’s Daydream rolled around and I had realized that while they made many improvements, there were still some fundamental issues that simply hadn’t been addressed. I’ve been advising companies to focus on standalone, and I’m glad I did. That said, I do believe that VR headsets that are powered by a smartphone via USB Type-C cable are a much more viable alternative to slot-in VR and should still deliver a high-quality experience. It would also speed up the ability of the VR headsets to gain access to 5G networks and faster SoCs.

Currently, the Snapdragon 855+ in devices like the OnePlus 7T and ROG II phone are scoring about 7,100 points in 3DMark’s Slingshot Extreme graphics test, while devices like the OnePlus 5T (running the same OS version) with a Snapdragon 835 is only getting 3800, slightly more than half. This is relevant because the Oculus Quest has a Snapdragon 835 which is a little more than half the performance of the fastest Android phones available today. That means a phone from today connected to a VR headset via cable would most likely consume less power and generate less heat than anticipated due to not needing to run very fast and probably still have better graphics than an Oculus Quest or Mirage Solo. Phone batteries have also grown, which should also handle prolonged usage better than previous generations.

Overall, slot-in smartphone-based VR headsets were a great way to start the growth of mobile VR. While nobody can for sure say they know what the future holds, it is pretty certain that smartphone slot-in VR is done and gone and Oculus killing Gear VR is probably the final nail in that coffin.

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