If nothing else, I think power consumption is a dealbreaker for a 20-year desktop PC. In (say) five years, there will be an iPhone with the same specs, and then you'll be running a desktop PC for 15 years at 100 times the power consumption for no reason. A good analogy is the way otherwise perfectly-good CRTs disappeared so quickly in favor of relatively expensive and low-contrast flat-panels. I'm using extreme numbers, but at that timescale even small efficiency increases will make it worth upgrading, and efficiency increases are a huge focus right now.

The place to look for a 20-year computer is probably the same place they are now -- embedded systems with minimal power consumption and ample specs for the limited job they're designed for. E.g., cars.

Interesting view which I had not thought of previously in quite that way.

Devil's advocate: My old workstation has a 440w power supply but uses much less than that most of the time. A small percentage of the total electrical power that my house uses. What pressure is there to switch the workstation for a more efficient PC?

Depends on OS developments. My 2006 Mac Pro is not supported under Mountain Lion, but it's still an excellent machine; 4 cores @ 2.66Ghz, 32GB of memory, and 6TB of disk. GigE, FireWire, USB, DVD/CDRom. I see no reason other than PC envy to upgrade to a different system. Eventually Apple will stop releasing security updates for Lion, and then I'll have to consider moving to a Linux distro. Short of a hardware failure I figure I'll get another 4-6 years out of it. Replacement parts for Mac Pros suck in price, but I bet I can find what I need on eBay. Heck, my system appears to be worth less than $500 according to my last search.

> Does anyone think a desktop PC with a 20 year life is possible now? What kind of design?

Probably not, I think hardware still moves too fast for it. A current PC might serve as a media center for that long, though.