One of the novelties of DirectX 12 Ultimate, the vitaminized version of the DX12 API, is DirectStorage. An API designed so that graphics cards can see memory beyond their own VRAM and access the content of the NVMe SSDs connected to the PCI Express hub of the system.
DirectStorage compatible with NVMe PCIe 3.0 SSDs
Last Tuesday, Microsoft made a presentation about the DirectStorage API, which is designed to speed up the copying of data, which is not accessible, from a GPU to an SSD. This feature is the same as what NVIDIA calls RTX IO, but within DirectX 12 Ultimate. Although Microsoft has confirmed that any GPU that is compatible with DX12 can make use of this API, they recommend activating it in those that meet the requirements of DX 12 Ultimate.
The relevant information that Microsoft has dropped, through the chat of its presentation, is that DirectStorage works with any of the NVMe SSDs that make use of a PCIe 3.0 or higher interface. Which puts an end to the rumor that DirectStorage would force the purchase of NVMe SSDs with PCI Gen 4 interface.
However, it is the GPUs compatible with DX12 Ultimate that have built-in accelerators for the decompression of data from the SSD inside. Being the case of the RTX 20 and RTX 30 from NVIDIA and the AMD RX 6000, the rest of the GPUs despite supporting DirectStorage will suffer an impact on their performance.
Decompression via Compute Shaders
DirectStorage allows data to be copied from SSD to VRAM without CPU intervention for decompression, what decreases the latency of access to such data by the GPU. Microsoft has created a number of Compute Shader programs that make these run on the GPU. So the same GPU cores that are used to render the game will be used to decompress the data.
Since it is a zero-sum game, this means that the graphics performance in games will be cut. Unless the GPU is equipped with a specialized drive to decompress data on the fly and manage access to the SSD. These drives as we have explained before are only found on the newer NVIDIA and AMD architectures.
Copying data from the SSD to the GPU in all cases means having to reserve an additional part of the system RAM to perform this function. So regardless of whether the GPU has a decompression unit or not, games that make use of DirectStorage to copy data from a PCIe 3.0 SSD onwards are going to require a greater amount of RAM.
SATA SSDs are out
If you have a SATA SSD then you will not be able to use DirectStorage, which is a jug of cold water for those who make use of these hard drives. The peculiarity of the PCI Express port is that from which the components and peripherals connected to it can communicate not only with the system RAM but with each other.
Because the SATA interface is different and does not have direct communication with the RAM, it not only has lower bandwidth and its copying system is much slower than through PCI Express. The objective is that the scenario has no apparent loads and that the data loads as quickly as possible while we play.
Developers will make use of DirectStorage sooner or later, so if you are considering updating your Gaming PC in the future then DirectStorage is a strong argument.