To fix the problem of not being able to install Windows 7 on an NVMe SSD, the first step you should take is download KB2990941 and KB3087873 patches. Thankfully, Microsoft has released an update with native drivers for Windows 7 which add NVM Express support. It was Windows 8.1 which first got support for NVMe.

But Windows 7 was only designed to work with SATA disks. They use a SATA connector if using SATA, otherwise the connector may be different depending on the form factor - in a desktop PC, they go into the PCIe slot, in an ultrabook, they use the M.2 connector. Most modern PCs come with SSDs which are use either SATA (AHCI) or NVM Express.