The Intel 4004 is a 4-bit central processing unit (CPU) released by Intel Corporation in 1971. It was the first microprocessor, and the first in a long line of Intel CPUs. The chip design, implemented with the MOS silicon gate technology, started in April 1970, and was created by Federico Faggin who led the project from beginning to completion in 1971. Marcian Hoff formulated and led the architectural proposal in 1969, and Masatoshi Shima contributed to the architecture and later to the logic design. The first delivery of a fully operational 4004 occurred in March 1971 to Busicom Corp. of Japan for its 141-PF printing calculator engineering prototype (now displayed in the Computer History Museum – Mountain View, Ca) . This calculator for which the 4004 was originally designed and built as a custom chip  was first commercially available in July 1971.