For our lines of high-speed PCIe® NVMe® SSDs, the Crucial System Scanner and Crucial System Advisor will list all M.2 PCIe NVMe SSDs not only for recently released compatible systems, but also for older systems using earlier revisions of the PCIe standard. In addition, systems without M.2 ports can be upgraded with aftermarket adapters which can be installed in earlier standards, or the adapters may comply with those standards themselves. 

Crucial SSDs are backward compatible with these older standards, but if you are seeing lower-than-expected performance it's important to verify your PCIe revision by reviewing your system or motherboard documentation from the manufacturer. Older standards, or systems where PCIe interfaces are using fewer data lanes as discussed in BIOS/UEFI Configuration for Optimizing M.2 PCIe®NVMe®SSDs, will reduce bandwidth and lower performance by at least half. The below table outlines maximum theoretical PCIe speeds by both PCIe generation and number of lanes, but note that due to system overhead and other hardware characteristics, real word numbers will be about 15% lower, and not exceed the rated speeds of the storage device itself.