Some people might have been discouraged, but not Babbage. Instead of simplifying his design to make the Difference Engine easier to build, he turned his attention to an even grander idea -- the Analytical Engine, a new kind of mechanical computer that could make even more complex calculations, including multiplication and division.
The basic parts of the Analytical Engine resemble the components of any computer sold on the market today. It featured two hallmarks of any modern machine: a central processing unit, or CPU, and memory. Babbage, of course, didn't use those terms. He called the CPU the "mill." Memory was known as the "store." He also had a device -- the "reader" -- to input instructions, as well as a way to record, on paper, results generated by the machine. Babbage called this output device a printer, the precursor of inkjet and laser printers so common today.
Babbage's new invention existed almost entirely on paper. He kept voluminous notes and sketches about his computers -- nearly 5,000 pages' worth -- and although he never built a single production model of the Analytical Engine, he had a clear vision about how the machine would look and work. Borrowing the same technology used by the Jacquard loom, a weaving machine developed in 1804-05 that made it possible to create a variety of cloth patterns automatically, data would be entered on punched cards. Up to 1,000 50-digit numbers could be held in the computer's store. Punched cards would also carry the instructions, which the machine could execute out of sequential order. A single attendant would oversee the whole operation, but steam would power it, turning cranks, moving cams and rods, and spinning gearwheels.
Unfortunately, the technology of the day couldn't deliver on Babbage's ambitious design. It wasn't until 1991 that his particular ideas were finally translated into a functioning computer. That's when the Science Museum in London built, to Babbage's exact specifications, his Difference Engine. It stands 11 feet long and 7 feet tall (more than 3 meters long and 2 meters tall), contains 8,000 moving parts and weighs 15 tons (13.6 metric tons). A copy of the machine was built and shipped to the Computer History Museum in Mountain View, Calif., where it remained on display until December 2010. Neither device would function on a desktop, but they are no doubt the first computers and precursors to the modern PC.