Who invented the abacus?
While the abacus in one form or another has been around for thousands of years, the abacus that we know of today first appeared around 1200 A.D. in China. No one particular person or group is considered to be the inventor as it likely evolved from various counting boards and bead systems over several centuries. The Chinese call this standard abacus a suan-pan. On each rod, this classic Chinese abacus has 2 beads on the upper deck and 5 on the lower deck (henceforth this type abacus is sometimes called a 2/5 abacus.) The 2/5 style survived unchanged until about 1850 at which time the 1/5 (one bead on the top deck and five beads on the bottom deck) abacus appeared.
Interesting facts about the abacus (you probably didn’t know)
Around 1600 A.D., use and evolution of the Chinese 1/5 abacus was begun by the Japanese via Korea. In Japanese, the abacus is called soroban. The 1/4 abacus, a style preferred and still manufactured in Japan today, appeared about 1930. The 1/5 models are rare today and 2/5 models are rare outside of China (except in some Chinese communities throughout the world).
It is thought that early Christians brought the abacus to the East (note that both the suan-pan and the Roman hand-abacus have a vertical orientation). Aspects of Roman culture could have been introduced to China as early as 166 A.D, during the Han Dynasty, as Roman emperor Antoninus Pius’ embassies to China spread along the Silk Road. Continued below:
There have been recent suggestions of a Mesoamerican (the Aztec civilization that existed in present day Mexico) abacus called the Nepohualtzitzin, circa 900-1000 A.D., where the counters were made from kernels of maize threaded through strings mounted on a wooden frame. There is also debate about the Incan Khipu— was it a three-dimensional binary calculator or a form of writing? (q.v. Talking Knots of the Incas).
Sources: Ryerson University Department of Electrical and Computer Engineering, and Wikipedia at http://en.wikipedia.org/wiki/abacus.