Windows 7 can be a PITA in such cases. From what I've seen, Windows 7 has started to show its age when it comes to hardware. Quite a bit of modern hardware like NVMe SSDs and USB 3 are not recognized out of the box. You're most stable bet would be to go with Windows 10 if you can. There'll be tradeoffs which I guess you are already aware of.

I attempted to install the exact same card (M.2 Samsung 950 Pro) into a NUC5I7RYH, as well as a backup SATA (Seagate 1TB Laptop Gaming SSHD (Solid State Hybrid Drive) SATA 6Gb/s 64MB Cache 2.5-Inch Internal Bare Drive (ST1000LM014)) - Neither one of them worked with Windows 7 out of the gate, and I ended spending a 4-6 hour odyssey of googling BIOS upgrades, Firmware Upgrades, and downloading various and sundry windows drivers (my final count was around 8-10 before all was said and done).

Ironically, we thought that Windows 7 would have had better support - but, as it turns out, for Circa 2H2015+ hardware, it's probably not a great platform. Here's hoping that Windows 10 stabilizes for a few years, and all the vendors agree to support that platform....

There is Windows update for 7/2008r2 which adds NVME support you need to cook it into the image.

Use this guide http://forum.notebookreview.com/threads/guide-installing-win... It worked for me. Also this :) http://www.samsung.com/semiconductor/global/file/insight/201...

I have a windows 2008R2 box at home running on a 950pro.

I used Ubuntu 16.04.

Windows 7 doesn't have M.2 drivers by default. See http://www.tomshardware.com/answers/id-2817439/install-windo... and good luck! I believe Windows 10 is fine though.

Windows 10 works well (M.2 Samsung 950 Pro on a Gigabyte GA-Z170X-UD5), but don't make the mistake I did of doing a default MBR-style format on the drive. Put the BIOS in UEFI mode and make sure the drive gets formatted with a GUID Partition Table (GPT).

With MBR the system would still take 30-60s to boot, but GPT reduced that to less than 10s.

You may need to copy the install data to a USB drive to get it to work. Initially I burned the iso image to a DVD and but then that DVD drive wasn't bootable under UEFI.

https://technet.microsoft.com/en-us/library/dn336946.aspx

Have you tried Windows 10 on it? Windows 7 is pretty old now and doesn't have much support for newer hardware. Your performance would be much better on Windows 10.

My bet is 64bit Linux

Dis you change bios to ahci instead of ide for the disk?

I am guessing a flavor of Linux.