Three months ago we got a new computer for our son Marc, and of course it came with Windows Vista, although Ana and I are still using Windows XP on our own computers.
From Marc's point of view, a computer is a games machine, and I was apprehensive about how many of his old games would work under Vista. I reassured myself that Vista seems not very different from XP; and at first I was pleased to find that some old games worked without trouble.
However, by now we realize that a number of his old games don't seem to work under Vista, although they work under XP.
This is a nuisance, and it's just an example of a wider problem with software: that it has a short lifespan. When I buy a book, I expect it to last for decades; it may well outlast me. But software can become unusable after only a few years, generally because of changes to the operating system.
Of course, if you maintain a museum full of computers running old operating systems, then you can go on running your old programs. But that's inconvenient and ultimately not very feasible. After a while, the old computers will break down and the old operating systems may not work with a new computer.
Some programs last longer than others. I'm still using Lotus Magellan, a file browser and search program, which hasn't been updated since 1990. It was an excellent program ahead of its time; it's somewhat less useful now because it's operating in a very different environment from what it was designed for. However, amazingly, it still works, and it's still useful for some purposes. I suppose this is because it was written for DOS, and so most of the changes to Windows in the last 18 years haven't affected it.