Charles Babbage famously designed two early computers starting in the 1830s: the Difference Engine and the Analytical Engine. Equally famously, neither computer was actually built in his lifetime. What happened?
In this 12-minute talk, John Graham-Cumming walks us through the various challanges Babbage faced, and explains the profound thinking Ada Lovelace brought to the project. (Note: the Difference Engine was eventually built using original schematics; here's a demo of it. Graham-Cumming is still working on building the Analytical Engine.)
Related reading: Ada Lovelace: The First Computer Programmer. (She programmed the Analytical Engine.)