PCIe (Peripheral Component Interconnect Express) is a well-established and versatile interface. Because of its prevalence (used for Graphic Cards etc.) and high data throughput capability PCIe was adopted by the storage industry to replace the much older and constrained SATA interface for the next generation of SSDs.
Adoption of PCIe, combined with other factors, enable NVMe™ SSDs to outperform SATA based SSDs by a factor of 6-7, with significant upward potential in the future thanks to the scalability of PCIe.