Are computers assumed to have operating systems?

[mr-friendly]

The listing said almost nothing about the computer, but merely provided a link to the manufacturer's website. This website clearly states that all computers of the same model come with Windows 7. I didn't think to ask and understood the link to be an accurate description, and now I have recieved a laptop with no operating system. Is this my mistake for not asking first, or is a link to specs part of the item description? On eBay, is a computer labelled as "Everything works fine" expected to have a functional operating system installed?

[robot-hands]

It's not magic. The computer runs the OS not the other way around.

[adx-computing]

Windows 10 key's are now tied to each systems motherboard. The only versions of Windows 10 that you can transfer is a windows 10 full version which retails for around $150-$200. The convenience with having the keys tied to the motherboard is quite good. Once you input the key you never have to enter it again even if you wipe your hard drive and do a full clean install.