Throughout time, humans have invented ingenious calculating machines. One of the earliest was the abacus. It's about 5,000 years old. Mechanical calculators that could add and multiply (but not subtract!) were invented in the 1600s. In 1820, Charles Xavier Thomas de Colman invented the arithmometer, a machine that could add, subtract, multiply and divide. It was Charles Babbage though, in the early 1800s, who designed mechanical calculating machines that were the true ancestor of today's computers. Ada Byron King (Countess of Lovelace) was his programmer and today is considered the mother of computer programming.
Babbage's design for his ultimate calculator, the Analytical Engine, was never produced. It did anticipate the four components essential to modern computing. These components are input, storage, processing and output.
The problem with Babbage's and other mechanical calculators was just that—they were mechanical. The moving parts they relied on were slow and subject to breakdown.
What made modern computers possible was the invention of something that could do calculations and other information processing with no moving parts and do it very fast. That something was electronic components. With electronic components, a fast and efficient machine such as Babbage proposed could be built with all four components essential to modern computing.