Editing Intel 4004 (section)

===Simplified design===
[[File:Chip_layout_from_the_development_phase_of_the_Intel_4004_from_1971,_the_first_microprocessor_of_the_world_(cropped_and_edited_image).jpg|thumb|Chip layout from the development phase of the Intel 4004]]

A key concept in the Busicom design was that the program control and ALU were not aimed specifically at the calculator market, it was the program in ROM that turned it into a calculator. The original idea was that the company could use the same chips with different amounts of shift-register RAM and program ROM to produce a range of calculating machines. Hoff was struck by how closely the Busicom's [[instruction set architecture]] matched that of general-purpose computers. He began to consider whether a truly general-purpose processor could be made cheaply enough to be used in a calculator.{{sfn|Faggin|Hoff|Mazor|Shima|1996|p=12}} When later asked where he got the ideas for the architecture of the first microprocessor, Hoff related that [[Plessey]], "a British tractor company",<ref>Possibly he had confused the Plessey name with that of [[Massey Ferguson]], makers of agricultural machinery.</ref> had donated a minicomputer to [[Stanford]], and he had "played with it some" while he was there. [[Tadashi Sasaki (engineer)|Tadashi Sasaki]] attributes the idea to break the calculator into four parts to an unnamed woman from the Nara Women's College present at a brainstorming meeting that was held in Japan prior to his first meeting with Intel.<ref>{{cite web
 |url        = http://www.ieeeghn.org/wiki/index.php/Oral-History:Tadashi_Sasaki
 |title      = Oral-History: Tadashi Sasaki
 |last       = Aspray
 |first      = William
 |date       = May 25, 1994
 |work       = Interview #211 for the Center for the History of Electrical Engineering
 |publisher  = The Institute of Electrical and Electronics Engineers, Inc.
 |access-date = January 2, 2013
}}</ref>

Another development that allowed this design to be made practical was Intel's work on the earliest [[dynamic RAM]] (DRAM) chips. Shift registers at that time were among the only low-cost read and write memory devices. However, [[shift register memory]] is not suited for random access, as each access must wait for the desired bit to flow through the chain. DRAM, on the other hand, allows random access, and the three transistor DRAM cell saves silicon area compared to the six transistor shift register cell.{{sfn|Faggin|Hoff|Mazor|Shima|1996|p=12}}

Finally, Hoff noticed that much of the complexity of the program control chip was due to every instruction being implemented separately. He suggested that the chip instead support [[subroutine]] calls and instructions be implemented as subroutines where possible. The application naturally suggested a 4-bit design, as this allowed direct manipulation of [[binary-coded decimal]] (BCD) values used by calculators. Hoff worked on the overall design concept through July and August 1969 but found that the Busicom executives seemed uninterested in his proposal.{{sfn|Faggin|Hoff|Mazor|Shima|1996|p=12}} Intel had to work smarter so Busicom would accept their proposal for the 141-PF calculator. They began to conceptualize a general purpose microprocessor that could be given instructions and return their results, as well as be able to merge all of the CPU functions of a computer.<ref name="3MinOn">{{cite video|url=https://m.youtube.com/watch?v=cVD5qKIY6ZM|date=November 20, 2014|title=3 Minutes On... The Intel 4004 Microprocessor|author=3 Minutes On...|work=[[YouTube]]|access-date=March 6, 2025}}</ref> Later in fall of that year, Intel's engineers proposed a new design of just four chips, including one that could be programmed for use; the programmable chip would end up becoming the 4004 microprocessor.<ref name="IntelEra"/>