Windows 8 (and 8.1) is considered to be one of Microsoft's biggest failures. They attempted to make an OS that worked on "everything" - including phones, tablets, etc. What they ended up with was a hybrid of formats that did not work well on either. It is no longer sold (they got rid of it while they were still selling Wind 7) and so good like finding a copy of it. Also it was o bad that many companies never made drivers for their hardware for Windows 8. So it will not run on most older computers.
The hardware requires for Windows 7, Windows 8 and Windows 10 are the same. So if your PC will run Windows 7, it will run Windows 10. There are drivers available. And if there are not, they did a good of job of getting it to work with 90% of hardware without drivers. It cost the same as a copy of Windows 8/8.1. It works better. It does not crash all the time like 8. It is more secure. And Microsoft is still selling and supporting it, which means you will get at least 5 to 10 years of life from it (support wise.) There is no support for win 8.
If you are thinking of upgrading (and you should), skip Win 8 and go to Win 10.