Great article in Wired at: http://www.wired.com/news/columns/0,71763-0.html?tw=rss.index
At first sight, a computer is a system that seems "clean." Early mainframes were housed in dust-free rooms bathed in unvarying white light. Nobody ever got physically dirty handling a laptop. The computer-using proverb "garbage in, garbage out" is just a metaphor; nothing physical goes into a computer, and nothing physical comes out of it.
Then again, why would a "clean" system require so many filters? Spam filters, search filters, surf filters? Why would stuff we encounter on a computer screen be capable of making us feel dirty, or "infecting" our clean machines with a virus?
Just as every animal has a mouth and an ass, with processing stuff in between, a computer operating system has inputs, processing and outputs. We input content through a keyboard, a modem, a drawing tablet, USB or Firewire ports. Useful stuff is output via screen, printer, speakers or over the internet. The useless stuff -- dirty old computer waste -- leaves the system via a little desktop metaphor called the Recycle or Trash bin.
It might be refreshing if, one day, the people who made your computer's OS would call a spade a spade. In a section of his conference talk titled "The Geometry of Filth," Adam Jasper Smith gets to the uncomfortable yet unavoidable nub of the matter. "Dirt radiates out from us," he says. "The primal form of this dirt -- the perfect dirt -- is shit."