That's about how frequently we replace office boxes. So this isn't simply an academic question. Soon you'll deal with it yourself. And you have options. You'll find lots of links to information on how and where to give away your old computer.
Schools top the list, but nonprofits are also hungry for boxes.
In fact, charities are often more eager to get their paws on computers. That's because school funding usually includes money for computers, but charities frequently scramble for every dollar and anything that stretches their resources is welcome. But. . . the plain truth is not every computer is wanted by charities. It's devilishly difficult to tweak older machines to connect to the Net and impossible to coax them into running current software. They re odd men out and having them around does nothing good.