Another possible option would be to remove the original hard drive and replace with a new sata drive and then install the windows 8.1 on that drive. I am not sure if I would be able to re insert the original windows 7 hard drive in the event that I did not like the new windows 8.1
That is the best way. Get another hard drive. You can switch between the 2 without problem. You can even leave both hard drive installed in your PC and just choose at start up which hard drive to boot from. That's what I do. I boot up from any of the 2 SSDs on my PC running Win 7 and 8. I just pull out the SSD tray that I don't want to boot up with.
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I am not very sure but I think the BIOS setting is only needed if you are coming from Win 8 down to Win 7 (compatibility support module or CSM is required to downgrade to Win 7). In my case, I didn't have to do any change in BIOS settings to run Windows 8. I just popped in the hard drive and Win 8 installer. That's it. I hope someone else could verify that here. I also have an HP with UEFI disabled by default. But if you just go ahead and try, it won't harm your system in any way. Just make sure the Win 7 hard drive is disconnected.
Btw, before you start the installation, go to HP support website first and download all the drivers for your hardware compatible with Windows 8.
http://h10025.www1.hp.com/ewfrf/wc/pfinder?tmp_product=HP ENVY 700&tmp_qt=driver download&cc=us&lc=en&dlc=en&product=5371495&tmp_searchExperience=0#N51
If you don't like the Win 8, just swap the drives back again. you don't have to do anything. Windows 7 and it's drivers are intact in its original hard drive. As I said, you can switch between the 2 OSes anytime without having to worry about anything. You don't need the CSM. Your PC is already running Win 7. You only need the CSM if your PC originally came with Windows 8.I know windows 8 will load and run just fine on the desktop. My concern is going back to windows 7 pro. I will be using 2 different hard drives. When I install windows 8 it will be on a new wiped hard drive. Once I decide which operating system I like best that is the one that will stay in the desktop. I will also make a backup image of each install just for peace of mind. Where do I get the CSM?
Thanks for all your help
If you don't like the Win 8, just swap the drives back again. you don't have to do anything. Windows 7 and it's drivers are intact in its original hard drive. As I said, you can switch between the 2 OSes anytime without having to worry about anything. You don't need the CSM. Your PC is already running Win 7. You only need the CSM if your PC originally came with Windows 8.
Edit:
Btw, CSM isn't something that you download. It's a feature in UEFI system that you need to enable to make a Windows 8 PC compatible with Windows 7. You don't have to worry about this.
If you don't like the Win 8, just swap the drives back again. you don't have to do anything. Windows 7 and it's drivers are intact in its original hard drive. As I said, you can switch between the 2 OSes anytime without having to worry about anything. You don't need the CSM. Your PC is already running Win 7. You only need the CSM if your PC originally came with Windows 8.
Edit:
Btw, CSM isn't something that you download. It's a feature in UEFI system that you need to enable to make a Windows 8 PC compatible with Windows 7. You don't have to worry about this.