I've been seeing a number of threads regarding Windows 7 support on 6th Gen processors, and instead of replying to each and every one, I thought I'd share my experience and knowledge in one place.
I am successfully running Windows 7 on a new Optimus VII (i7-6700HQ) with all hardware working correctly - review to follow soon! Please note that PCS states that W7 may not be compatible with a number of models, and I can only confirm 100% that W7 works on my system. I have split this into two sections - Installation and Drivers.
Installation
This may be one reason PCS does not offer W7 - the installation can be tricky. Installing via CD shouldn't be an issue but most of us probably don't have a disk drive (e.g. need to sacrifice for second HDD or is not offered at all), so will need to install through USB (or via LAN which I will not cover). As I'm sure you know, make sure you create a bootable USB from the W7 iso (Google how - Microsoft provides a tool, or use something like Rufus).
Additionally, disable UEFI in BIOS settings.
The Optimus VII only has USB 3.0 ports and I assume this is true for most of the higher-end PCS models. The W7 pre-installation environment does not support USB 3.0. As soon as the W7 PE is loaded into memory, an error will be presented: "A required CD/DVD drive device driver is missing. If you have a drover floppy disk, CD, DVD or USB please insert it now". This is because the W7 PE has no USB 3.0 drivers and therefore cannot read from the USB. There are three options:
1) BIOS Legacy USB
There may be an option in your BIOS to select legacy/USB 2.0 in which case installation should be easy. However, my Optimus VII has no such option.
2) Slipstream the USB 3.0 drivers into the W7 image
You will need access to an operational Windows system for this method, which involves injecting the correct USB 3.0 drivers into the mounted USB, so that no installation errors will occur.
Download the USB 3.0 drivers for 6th Gen CPUS from Intel:
https://downloadcenter.intel.com/download/22824/USB-3-0-Driver-Intel-USB-3-0-eXtensible-Host-Controller-Driver-for-Intel-8-9-100-Series-and-C220-C610-Chipset-Family
Then, follow these instructions:
http://codeabitwiser.com/2014/03/how-to-install-windows-7-with-only-usb-3-0-ports/
NB: Do not download the drivers linked in the instructions above - these are not for 6th Gen
Alternatively, Intel provides a utiltiy which I believe does the same automatically, although I have not tested this, and you will need to replace the drivers which the tool comes with with the correct drivers.
https://downloadcenter.intel.com/download/25476/Windows-7-USB-3-0-Creator-Utility
3) Host the USB 3.0 drivers on another disk/partition
If you do not have access to a Windows system, copy the USB 3.0 drivers onto another disk/partition where W7 will not be installed (e.g. by booting into a live OS such as Linux via USB).
Once copied, boot the W7 USB and you will be presented with same error, however this time you will be able to point the program to the USB 3.0 drivers which it will load. Load the HCSwitch driver first and then the Win7 driver.
This method may seem a little easier than method 2 but I wanted to create a permanent W7 'recovery disk' so I'd recommend the slightly longer route.
Drivers
Another reason PCS may not offer W7 is because Clevo do not provide any drivers on their support page (PCS use Clevo chassis for their laptops). However, other manufactures using the same Clevo chassis do offer W7 such as Sager and Xotic PC, so I have used Sager drivers.
Firstly, check your Clevo chassis model here:
http://www.pcspecialist.co.uk/laptops/clevo-laptops/40/
Then, download and install the corresponding W7 drivers for your model here:
http://www.sagernotebook.com/drivers.php
It's also worth opening Device Manager and using Windows Update to search for drivers, although I have had difficulties with Windows Update - it seems to hang on "Checking for Updates" (even after activation).
You may not find W7 drivers for every device - I'd recommend trying the W10 driver (worked for my fingerprint scanner if I recall correctly) or just Google the device.
Hopefully, like me, you will now be able to enjoy your old but favourite Windows 7 OS on a brand new system! Please let me know if anything is unclear or if you are having any difficulties.
I am successfully running Windows 7 on a new Optimus VII (i7-6700HQ) with all hardware working correctly - review to follow soon! Please note that PCS states that W7 may not be compatible with a number of models, and I can only confirm 100% that W7 works on my system. I have split this into two sections - Installation and Drivers.
Installation
This may be one reason PCS does not offer W7 - the installation can be tricky. Installing via CD shouldn't be an issue but most of us probably don't have a disk drive (e.g. need to sacrifice for second HDD or is not offered at all), so will need to install through USB (or via LAN which I will not cover). As I'm sure you know, make sure you create a bootable USB from the W7 iso (Google how - Microsoft provides a tool, or use something like Rufus).
Additionally, disable UEFI in BIOS settings.
The Optimus VII only has USB 3.0 ports and I assume this is true for most of the higher-end PCS models. The W7 pre-installation environment does not support USB 3.0. As soon as the W7 PE is loaded into memory, an error will be presented: "A required CD/DVD drive device driver is missing. If you have a drover floppy disk, CD, DVD or USB please insert it now". This is because the W7 PE has no USB 3.0 drivers and therefore cannot read from the USB. There are three options:
1) BIOS Legacy USB
There may be an option in your BIOS to select legacy/USB 2.0 in which case installation should be easy. However, my Optimus VII has no such option.
2) Slipstream the USB 3.0 drivers into the W7 image
You will need access to an operational Windows system for this method, which involves injecting the correct USB 3.0 drivers into the mounted USB, so that no installation errors will occur.
Download the USB 3.0 drivers for 6th Gen CPUS from Intel:
https://downloadcenter.intel.com/download/22824/USB-3-0-Driver-Intel-USB-3-0-eXtensible-Host-Controller-Driver-for-Intel-8-9-100-Series-and-C220-C610-Chipset-Family
Then, follow these instructions:
http://codeabitwiser.com/2014/03/how-to-install-windows-7-with-only-usb-3-0-ports/
NB: Do not download the drivers linked in the instructions above - these are not for 6th Gen
Alternatively, Intel provides a utiltiy which I believe does the same automatically, although I have not tested this, and you will need to replace the drivers which the tool comes with with the correct drivers.
https://downloadcenter.intel.com/download/25476/Windows-7-USB-3-0-Creator-Utility
3) Host the USB 3.0 drivers on another disk/partition
If you do not have access to a Windows system, copy the USB 3.0 drivers onto another disk/partition where W7 will not be installed (e.g. by booting into a live OS such as Linux via USB).
Once copied, boot the W7 USB and you will be presented with same error, however this time you will be able to point the program to the USB 3.0 drivers which it will load. Load the HCSwitch driver first and then the Win7 driver.
This method may seem a little easier than method 2 but I wanted to create a permanent W7 'recovery disk' so I'd recommend the slightly longer route.
Drivers
Another reason PCS may not offer W7 is because Clevo do not provide any drivers on their support page (PCS use Clevo chassis for their laptops). However, other manufactures using the same Clevo chassis do offer W7 such as Sager and Xotic PC, so I have used Sager drivers.
Firstly, check your Clevo chassis model here:
http://www.pcspecialist.co.uk/laptops/clevo-laptops/40/
Then, download and install the corresponding W7 drivers for your model here:
http://www.sagernotebook.com/drivers.php
It's also worth opening Device Manager and using Windows Update to search for drivers, although I have had difficulties with Windows Update - it seems to hang on "Checking for Updates" (even after activation).
You may not find W7 drivers for every device - I'd recommend trying the W10 driver (worked for my fingerprint scanner if I recall correctly) or just Google the device.
Hopefully, like me, you will now be able to enjoy your old but favourite Windows 7 OS on a brand new system! Please let me know if anything is unclear or if you are having any difficulties.