You wouldn’t expect that from a mod Portal: Prelude RTX would introduce such an important piece of gear for the future of PC gaming. But lo and behold – it’s the first game we’ve seen with Nvidia’s new RTX IO, a feature that was announced almost three years ago.
It’s not as flashy as ray tracing or DLSS, runs in the background, and offers a range of benefits without drawing attention. But according to my testing, RTX IO could have a bigger impact on PC gaming than any other RTX feature.
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What is RTX IO?
Portal: Prelude RTX | RTX IO Off vs On Comparison – Cake Scene
First, let’s talk about what RTX IO even is. It’s GPU-accelerated asset loading and decompression that promises faster load times, smaller install sizes, lower CPU usage, and fewer texture pop-ins. It does this by offloading some of your CPU’s work to the GPU and taking advantage of the massive number of cores available on graphics cards.
When games load normally, assets are removed from the SSD and loaded into system storage. They return from memory to your CPU for decompression before returning to memory. Once the entire asset is ready, it will be sent to the graphics card. This system has worked for a long time, but now there’s a problem with it: the PS5 and Xbox Series X.
As I’ve written before, both the PS5 and Xbox Series X have special decompression hardware that completely takes the CPU out of this process. Assets are decompressed faster and therefore reach the GPU faster. The memory in PCs these days is fast enough to keep up with this level of streaming, but they lack the dedicated decompression hardware to make it possible. This is where RTX IO comes in.
Compressed data is transferred from the SSD to the system memory and goes directly to the GPU. It is routed through GDeflate, Nvidia’s open-source data compression scheme for GPUs, and is immediately available on the GPU.
If you keep up with this technology, you can probably see the similarity to Microsoft’s DirectStorage. RTX IO works on DirectStorage and even supports Vulkan extensions so it works in games like… Portal: Prelude RTX. Again, none of this is proprietary; Nvidia has had a lot of arguments about its (now open-source) Deep Learning Super Sampling, but RTX IO works on any DirectX 12 graphics card.
But does it work?
It’s all great in theory, but GPU decompression is new territory on PC – even in games like Pronounced that support DirectStorage. You don’t have to look any further than the install size to see that RTX IO works. If you would download Portal: Prelude RTX Right now you’ll see it’s around 24GB (exactly 24.29GB at the time of writing). With the RTX IO off, the total install size is 39.16 GB. That’s a 38% reduction in install size for the exact same game.
Loading the textures was much also faster. In one scene, the textures took 3.13 seconds to load with the RTX IO off, with a noticeable pop-in. With the RTX IO on, they were there in 1.36 seconds. In the most demanding scene I watched, the textures took 6.34 seconds to load with the RTX IO off. Switched on, they were there in just 2.51 seconds.
Note the scope of Portal: Prelude RTX, as well as. It’s a game of depth, not breadth, offering extensive path tracing and highly detailed materials for every angle of a scene. With a larger game, it’s not hard to see the benefits of RTX IO for texture streaming. With the right optimization and RTX IO cutting about two-thirds of the time it takes to stream textures, there are some clear applications in large open-world games.
CPU usage also dropped. In the demanding scene I mentioned above, utilization peaked at 37% (and that’s with the monstrous 24-core Intel Core i9-13900K). When you turn on RTX IO, the value has dropped to 22%. As far as I could tell, it seemed so Portal: Prelude RTX scaled to eight cores. Some games, especially those made with the Unreal Engine, could get more benefit from being limited to a few cores.
What this means for PC gaming
Make no mistake: Portal: Prelude RTX is a taste of what games using this technology could look like in the future. Luckily we won’t have to wait long to see what it can do in other games. Nvidia confirmed Ratchet & Clank: Rift Apart will support RTX IO on PC, allowing it to run this game’s memory-intensive design.
What excites me the most are the optimization benefits that RTX IO (and DirectStorage, for that matter) can bring. I’ve been vocal about the fact that it’s a bad time for PC gamers, and that’s largely due to the continued stuttering of major AAA releases. Hardware accelerated decompression does not solve the PC stuttering problems, but it can help.
As we have seen in games like Star Wars Jedi: Survivor, Dead Space, And redfall, Traversal stuttering is still a very real problem on PC. This is particularly problematic when games are designed to run on only a few CPU threads (as is the case with Unreal Engine titles). Star Wars Jedi: Survivor And redfall). By taking some of the work out of these cores in the decompression department, they can now, well, run the game and hopefully avoid some of the biggest traversal stuttering issues we’ve seen this year.
If that’s the case, RTX-IO and GPU decompression is a big step towards PC gaming support. Faster load times and smaller install sizes don’t hurt, but hopefully the real benefit of something like this lies in its ability to reduce stuttering in games that stream huge assets in and out of the game world.
It appears that this will be the case. Here’s how Nvidia explained it: “RTX IO alone cannot completely eliminate stuttering, but it can be an assistive technology to reduce stuttering.” This can be achieved by reducing dependence on CPU processing power when the need arises Loading textures and geometries “faster” is the cause of stuttering and frees up the CPU to work on other tasks.”
For now we just have to wait to see more games with RTX IO and other branded GPU decompression technologies. Ratchet & Clank Rift Apart It launches on July 26th, but we’re hoping to see more games using this technology later in the year.