"The Incas used a computer. We do not know how it worked or how the calculations were made, nor do we know what they were calculating. The device was a box with twenty compartments placed in four rows of five. Stones were placed in the various compartments, some black, some white. A compartment was filled when five stones were in it. Padre Jose de Acosta watched the Incas manipulate this abacuslike device and drew a sketch. But that was back in 1590. He was unable to follow the computing procedure. None of these 20-core memory banks have been found by archaeologists. Were they destroyed as worthless, pagan magic?"
Text and image from Beyond Stonehenge, by Gerald S. Hawkins (Dorset Press, 1973). The other relevant item in the image is a quipu, explained here.
Two other things I learned from the book. There is an Arctic Circle for the moon (equivalent to the solar Arctic Circle we are all familiar with).
Also: "Astronomers recognize A.D. 0 but historians do not. They count B.C. 2, B.C. 1, A.D. 1..."