Compared to the incumbent technology, the SGT integrated on the same chip area embodied twice the number of transistors with five times the operating speed.

The first delivery of a fully operational 4004 was in March 1971 to Busicom for its 141-PF printing calculator engineering prototype (now displayed in the Computer History Museum in Mountain View, California).

The main concept was the use of the self-aligned gate, made of polysilicon rather than metal, which allowed the components to be much closer together and work at higher speed.

Together, these innovations doubled the circuit density, and thus halved cost, allowing a single chip to contain 2,300 transistors and run five times faster than designs using the previous MOS technology with aluminum gates.

In late June, three engineers from Busicom, Masatoshi Shima and his colleagues Masuda and Takayama, traveled to Intel to introduce the design.

He raised these concerns with upper management, and Bob Noyce, the CEO, told Hoff he would support a different approach if it seemed feasible.

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.

[9] When later asked where he got the ideas for the architecture of the first microprocessor, Hoff related that Plessey, "a British tractor company",[10] had donated a minicomputer to Stanford, and he had "played with it some" while he was there.

[11] Another development that allowed this design to be made practical was Intel's work on the earliest dynamic RAM (DRAM) chips.

One key issue was that certain routines like decimal adjust and keyboard handling would use large amounts of ROM space if implemented as subroutines.

In April 1970, Leslie Vadász, who ran the MOS design group, hired Federico Faggin from Fairchild Semiconductor to take over the project.

Integrated circuits consist of a number of individual components like transistors and resistors that are produced by mixing the underlying silicon with "dopants".

In 1967, Bell Labs released a paper about making MOS transistors with self-aligned gates made of silicon rather than metal.

Faggin and Tom Klein had taken what was a curiosity and developed the entire process technology needed to fabricate reliable ICs.

Faggin also designed and produced the Fairchild 3708,[16] the first IC made with SGT, first sold at the end of 1968, and featured on the cover of Electronics in September 1969.

It also allowed the highly-doped silicon used for the gates to form the interconnections, greatly improving the circuit density of random-logic ICs like microprocessors.

Previously the interconnects had to be much larger than required in order to ensure the aluminum touched the silicon components which would be offset due to inaccuracies in the machinery.

[26] Hoff and Mazor were also concerned that the design's limitations would make it less interesting to users who were accustomed to the new 16-bit minicomputers entering the market at that time.

[27] This all changed in the summer of 1971, when Ed Gelbach, formerly of Texas Instruments, took over the marketing department and immediately began plans to publicly announce the product.

The tradeoffs between the two designs were that with the 4004 and its memory and I/O chips it was much easier to build a complete computer system while the 8008 was more flexible, had a larger 16 kB address space, and offered more instructions.

A significant difference is that while a minimal 4004 system could be built using only two chips, one 4004 and one 4001 (256-byte ROM), the 8008 would require at least 20 additional TTL components for interfacing with memory and I/O functions.

The 4004 was used where the cost of implementation was the major concern, and became widely used in embedded controllers for applications like microwave ovens or traffic lights and similar roles.

[citation needed] The Intel 4004 was fabricated using masks produced by physically cutting each pattern at 500x magnification on a large sheet of Rubylith photo-reducing it, and repeating, a process made obsolete by current computer graphic design capabilities.

[35] The 4004 includes functions for direct low-level control of memory-chip selection and I/O, which are not normally handled by the microprocessor; however, its functionality is limited in that it cannot execute code from RAM and is limited to whatever instructions are provided in ROM (or an independently loaded RAM working as ROM—in either case, the processor is itself unable to write or transfer data into an executable memory space).

This partitioning significantly reduced the minimum part count in an MCS-4 system, but required inclusion of a certain amount of processor-like logic on the memory chips themselves to accept, decode and execute relatively high-level data-transfer instructions.

Intel's MCS-4 documentation, however, claims that up to 48 ROM and RAM chips (providing up to 192 external control lines) "in any combination" can be connected to the 4004 "with simple gating hardware", but declines to give any further detail or examples of how this would actually be achieved.

The minimum system specification described by Intel consists of a 4004 with a single 256-byte 4001 program ROM; there is no explicit need for separate RAM in minimal-complexity applications thanks to the 4004's large number of onboard index registers, which represent the equivalent of 16 × 4-bit or 8 × 8-bit characters (or a mixture) of working RAM, nor for simple interface chips thanks to the ROM's built-in I/O lines.

The earliest versions, marked C (like C4004), were ceramic and used a zebra pattern of white and gray on the back of the chips, often called "grey traces".

On September 17, 1971 (two months before the 4004), the Texas Instruments TMS0100 (originally designated TMS1802NC) was announced as a "calculator on a chip" that integrated a CPU with ram and a program read-only memory.

[49] On October 15, 2010, Faggin, Hoff, and Mazor were awarded the National Medal of Technology and Innovation by President Barack Obama for their pioneering work on the 4004.