usulay computer manufacturers sell their boxes with a OS ...
a few years ago i bought a compaq box with 98 on it. when i upgraded the box ... actualy i bought a new one .. compaq also they said that the other one was sold with the os incorporated and that cannot be reused on other machines due to licence stuff
on the cd was written "for distribution with PC serial XXXXXXXX"
but it works fine on others... problem is that this is illegal. U have to notify the vendor and ask for a new licence when u wanna put it on other box than the original one. in this matter i had to make a statement where i declared that my old comp will not be used anymore and that the licence moved on the new one.
with OS's bought separately... u can sell it ... be sure to have some sort of evidence that u sold it and be sure not to use it after u sold it...
this exists is in perfectly legal world
