If you use a PCI-e NVMe SSD as a data disk in Windows 7, you should set the BIOS settings as [RAID] and [UEFI with CSM] mode before installing Windows 7. Otherwise, your PCI-e NVMe SSD might not be detected in the Intel Rapid Storage Technology (IRST) control panel, and it will cause the limitation of NVMe features.
To use a PCI-e NVMe SSD as a data disk, please set the BIOS setting as below and reinstall Windows 7.
SATA Mode Selection: [RAID]
Boot mode select: [UEFI with CSM]