I would like to install Linux on an old laptop. what is the best Linux distribution for weak hardware on a mechanical HDD, I already use Linux mint on my main computer but I would like something more lightweight for an pentium based laptop
The most lightweight distro available with mint being one example of such, you may consider Lubuntu which unlike Mint uses LXDE as its desktop environment. Also distributions specifically targeted at older hardware such as Puppy Linux or Salix are worth considering if you need anything more lightweight still.