Grant got the reason about the version skip correct. You might want to check out a few things before you try to swap 8.1 for 7. At least on some of the newer computers. Part of the identifier for the OS is written on the motherboard. I swapped 8 for 7 in an HP Pavilion with no problem but when i tried the same on this one when it was less than a week old, I open a big can of worms. First off, I never got 7 to load and boot. Then I went through Dell tech support for a while (hours on three different occasions) and they sent me two versions of the 8.1, which loaded up and booted fine but would not let me "activate" with Microsoft. I wound up shipping it to Dell, at their expense, and they replaced the motherboard so an OS could be loaded that coincided with the software identifier code written into the motherboard. And while I don't currently work in IT, I do have a trade school certificate to repair and upgrade computers and also am Network + certified. You can check out the Comptia site to verify the last part. So I am more than familiar with working on computers.