Editing Intel 4004 (section)

===Into production===
[[File:Intel 4004 on Busicom calculator circuit board.jpg|thumb|Intel 4004 CPU and associated chips on the circuit board from a Busicom calculator]]

Intel's chip-naming scheme at that time used a four-digit number for each component. The first digit indicated the process technology used, the second digit indicated the generic function, and the last two digits specified the sequential number in the development of that component type. Using this convention, the chips would have been known as the 1302, 1105, 1507, and 1202. Faggin felt this would obscure the fact that they formed a coherent set, and decided to name them as the "4000 family".<ref name="FFsign">{{cite web |title=Federico Faggin's Signature |publisher=Intel4004.com |url=http://www.intel4004.com/sign.htm |access-date=August 21, 2012}}</ref> The four chips were the following:
* the ''Intel 4001'', a 256-byte 4-bit ROM;
* the ''Intel 4002'', DRAM with four 20-[[nibble]] registers (total size 40 bytes);
* the ''Intel 4003'', an I/O chip comprising a 10-bit static shift register with serial and parallel outputs; and
* the ''Intel 4004'' CPU. 
A fully expanded system could support 16 Intel 4001s for a total of 4&nbsp;kB of ROM, 16 Intel 4002s for a total of 1,280 nibbles (640 bytes) of RAM, and an unlimited number of 4003s. The 4003s were connected to programmable input and output pins on the 4001 and to output pins on the 4002, not directly to the CPU.{{sfn|Faggin|Hoff|Mazor|Shima|1996|p=11}}
[[File:Busicom 141 PF 1.jpg|thumb|[[Busicom]] 141-PF]]
With the design complete, Shima returned to Japan to begin building a prototype of the calculator. The first wafers of the 4001 were processed in October 1970,{{sfn|Faggin|Hoff|Mazor|Shima|1996|p=16}} followed by the 4003 and 4002 in November. The 4002 proved to have a minor problem that was easily corrected. The first 4004s arrived at the end of December, and were completely non-functional. Probing the chip, Faggin found that the buried-contact fabrication step had been left out. A second run was fabricated in January 1971 and the 4004 worked as expected except for two minor problems.

Faggin was sending samples of these chips to Shima as they arrived in February 1971.<ref name="IntelEra"/> In April of that year, they learned the calculator prototype was operational. Later that month Shima sent Intel the final masks for the 4001 ROMs, the design was now complete. It consisted of one 4004, two 4002, three 4003, and four 4001 chips. An additional 4001 supplied the optional square root function. One final change was added after Faggin found a problem in the 4001 and 4002 that occurred only when the chips were hot. Adding a new register decoder circuit in both solved the issue. Quantity production began in August 1971.{{sfn|Faggin|Hoff|Mazor|Shima|1996|p=17}}