"... You might be thinking that one can always take the bootable DVD route and even though research indicates that dependence on optical drives is diminishing by the second, it has its own caveats. You better hope that your motherboard has a PS/2 port because even while installing from a DVD, the USB ports wont work (during the install setup). If you have just one PS/2 port you will have to switch your PS/2 based mouse and keyboard as required through the entire process. All this means that Windows 7 will be very very troublesome for people to install and in most of the cases, people will consider it not worth the effort. Even if you do get it to work, the lack of EHCI means there might be unforeseen compatibility issues in the future. Effectively, from Skylake, and thanks to Intel’s spec upgrade, Windows 7 is now officially an obsolete OS ..."
"... One big shock will be for Windows 7 users. By default, the Z170 chipset and BIOS will not support full USB 2.0 Enhanced Host Controller (EHCI) mode. This means that for a number of circumstances, USB devices will not work unless an XHCI environment in play.
In our testing, this means that in order to install Windows 7 you need to do the following:
· Navigate to BIOS
· Enable ‘Windows 7 Installation’ or ‘EHCI mode’, Save and Exit.
· Have your Windows 7 image on an optical disk. USB sticks will not work!
· Install the OS as normal via the optical media. Install OS drivers/USB 3.0 drivers.
· Disable the BIOS option.
This is done for a couple of reasons. Firstly, it helps reduce the size of the BIOS for more customization. It also aids moving users to AHCI capable operating system installations. For everyone else, it is a bit of a headache. As far as we can tell, almost all motherboard manufacturers (at least the Tier-1s) will have this option in the BIOS to enable Windows 7 installation ..."
Edited by TELVM, 10 August 2015 - 01:04 AM.