If i buy a second hand computer with no hard drive what are my options these days for getting windows on there (clearly I’ll buy a hard drive)? It seems that it might be cheaper to buy a new PC with it already installed?

You can download it on another machine, stick it on a suitable sized USB stick and boot from USB. (Similarly you should be able to boot another OS from USB and then download direct to the drive – but that probably means Linux, and fun stuff like getting Wifi to play on Linux if you are not used to it).

Basically, that ^^

You can download W10 directly from Microsoft, they seem to have given up any pretence of caring about anyone paying for it these days. If the computer had W10 on it previously then it should Just Work and not trouble you for a licence key, if it didn’t then I probably wouldn’t want to be buying it anyway.

Don’t buy a hard drive, buy an SSD.

I meant an SSD! So even if its not got a drive installed but had W10 on previously then it shouldn’t need a key?

Yeh, the windows key, once used, is registered against that particular PC (motherboard) so it should in theory just re-register itself when you install it and you give it internet access.

Okay thanks, thats interesting!

Correct.

And if you sign in with a Microsoft account rather than a local login it converts the registration into to a digital licence and backs it up to your account, so (in theory at least, I haven’t tried it) you shouldn’t lose the entitlement if your motherboard goes pop.

Quite why they still bother and don’t just remove licensing requirements for home users I don’t know.