RE: Alienware X51 R2 formatting hard drive
I removed all partitions, switched BIOS options for Legacy, AHCI, SecureBoot Off, then I was able to install Win7.
Why Win 7? Some games require Games for Windows, which have issues under Win 10.
Not sure about Win 8/8.1, but simply don't want it.
Alienware X51 R2:
MSI GTX 950 OC,