Portal: Prelude RTX brings a classic Source mod to the forefront of graphics technology

Portal: Prelude RTX is an impressive showcase of Nvidia's RTX Remix technology, which takes what was once a Source mod for Portal and gives it visual features and technology that rival and even surpass high-end triple AAA releases. It is truly spectacular - and hopefully one of many path-traced remasters to come in the future as the RTX Remix modding tools approach release.

More interestingly though, Prelude is also the first game to support RTX IO, a GPU-accelerated decompression scheme running under Vulkan. This is essentially an Nvidia-branded version of Direct Storage 1.2, which is also included in Ratchet and Clank: Rift Apart which launches on PC later this month. Its purpose is to accelerate game loading and asset streaming on the PC platform, and its inclusion here gives us a good excuse to see how the technology works.

Historically, loading involved game data like textures or models being transferred from a hard drive to system memory and then on to the GPU under the control of the CPU. This was quite a latency-heavy, serial approach as the disk had to physically spin up the spindle, locate the data, then load the data block by block in a way that minimises the amount of seeking necessary.

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