Rowan -

The simple answer to "What is a technological dead end?" appears to be "Anything I've bought."

Computers are an obvious one, especially laptops. My "working perfectly" laptop that needed a memory upgrade to go to the next generation OS before it was a year old encountered "that memory chip is not made any more."

My digital camera uses the then (4 years ago) most popular memory card, which is now obsolete and replacements (or spares) unavailable.

About three months after I upgraded my camera to a brand new Canon A-1, partly because of the vast selection of available lenses, they announced a completely new and entirely incompatible line of lenses that I can't mount on mine, and mine won't mount on any of the new ones.

Within 30 days after I signed the mortgage on my camper, I visited the maker's website and found a big sign saying "MODEL DISCONTINUED, NO INFORMATION AVAILABLE" (and I've still got a years worth of payments left).

If I buy it, it will DISAPPEAR.

Especially if I like it.

(But I never bought a BetaMax.)

John