Windows – How to tell what version of Windows came on a laptop

Rather than discuss something I don't know or understand like many of the poster's above (who seem to be leveraging former experiences with prior OSes) I will state my experience and you can accept it for it is.

I purchased an ACER M5 with a pre-loaded OEM version of windows 8, similarly there was no affixed sticker stating the product key. I removed the original hard drive and upgraded to a new SSD. No efforts towards imaging or maintaining of the original HHD were performed. I purchased a system builders DVD for windows 8 pro to install onto the new, entirely blank SSD. During the installation, I was never asked to input a product key. My final istallation was a copy of windows 8 (non pro). Futhermore, a check on the last 5 digits of the product key applied on my installation reflected a different product key than the one shipped with the system builder DVD.

Speculation: the OEM product key was stored elsewhere on the machine, detected, and employed rather than asking the user to supply a product key. I've read elsewhere that the key is maintained in the BIOS for new OEMs from major PC manufactures to simplify reporting to Microsoft.

Personal: I build a new box every two years so the fact that my product key was never requested doesn't impact me; my purchased personal use license for W8 pro will be used eventually.

First, through trial and error in the Windows activation dialog, I discovered that the only possible characters are these (others are rejected): 2 3 4 5 6 7 8 9 B C D F G H J K M P Q R T V W X Y

The real breakthrough was this comment from Tom's Hardware:

"Old School technique worked for me. Soft lead pencil go over faded area gently so you don't tear sticker and my digits appeared..."

http://www.tomshardware.com/answers/id-1691850/windows-product-key-rubbed.html

Lightly rubbing with a soft (2B) lead pencil indeed clarified the characters I was missing.