White ceramic Intel C4004 microprocessor with grey traces
|Produced||From late 1971 to 1981|
|Max. CPU clock rate||740 kHz|
|Min. feature size||10 µm|
|Instruction set||4-bit BCD oriented|
|Data width||4 Bit|
|Address width||12 (multiplexed)|
|Application||Busicom calculator, arithmetic manipulation|
The Intel 4004 is a 4-bit central processing unit (CPU) released by Intel Corporation in 1971. It was the first commercially available microprocessor by Intel, and the first in a long line of Intel CPUs.
The chip design started in April 1970, when Federico Faggin joined Intel, and was completed under his leadership in January 1971. The first commercial sale of the fully operational 4004 occurred in March 1971 to Busicom Corp. of Japan for which it was originally designed and built as a custom chip. In mid-November of the same year, with the prophetic ad "Announcing a new era in integrated electronics", the 4004 was made commercially available to the general market. The 4004 was the first commercially available monolithic processor, fully integrated in one small chip. Such a feat of integration was made possible by the use of the then-new silicon gate technology for integrated circuits, originally developed by Faggin (with Tom Klein) at Fairchild Semiconductor in 1968, which allowed twice the number of random-logic transistors and an increase in speed by a factor of five compared to the incumbent MOS aluminum gate technology. Faggin also invented the bootstrap load with silicon gate and the “buried contact”, improving speed and circuit density compared with aluminum gate.
The 4004 microprocessor, the 4001 ROM, 4002 RAM, and 4003 Shift Register constituted the 4 chips in the Intel MCS-4 chip-set. With these components, small computers with varying amounts of memory and I/O facilities can be built.
Contemporaneous CPU chips
Three other CPU chip designs were produced at about the same time: the Four-Phase Systems AL1, done in 1969; the MP944, completed in 1970 and used in the F-14 Tomcat fighter jet; and the Texas Instruments TMS-1000 chip, announced in September 17, 1971. Both the AL1 and the MP944 use several chips for the implementation of the CPU function. The TMS0100 chip was presented as a “calculator on a chip” with the original designation TMS1802NC. This chip contains a very primitive CPU and can only be used to implement various simple 4-function calculators. It is the precursor of the TMS1000, introduced in 1974, which is considered the first microcontroller i.e., a computer on a chip containing not only the CPU, but also ROM, RAM, and I/O functions. The MCS-4 family of 4 chips developed by Intel, of which the 4004 is the CPU or microprocessor, was far more versatile and powerful than the single chip TMS1000, allowing the creation of a variety of small computers for various applications.
Zilog, the first company entirely dedicated to microprocessors and microcontrollers, was started by F. Faggin and Ralph Ungermann, at the end of 1974. These devices formed the basis for later models of microcontrollers.
History and production
The first public mention of 4004 was an advertisement in the November 15, 1971, edition of Electronic News. The first delivery was to Busicom for their engineering prototype calculator in March 1971, followed by their 141-PF prototype calculator commercially available in the market in July 1971. Packaged in a 16-pin ceramic dual in-line package, the 4004 was the first commercially available computer processor designed and manufactured by chip maker Intel, which had previously made semiconductor memory chips. The chief designers of the chip were Federico Faggin, the leader of the project after the architectural definition was finalized with Busicom, who created the design methodology and the silicon-based chip design; Ted Hoff who formulated the architecture, both of Intel, and Masatoshi Shima of Busicom who assisted in the development.
Faggin, the sole chip designer among the engineers on the MCS-4 project, was the only one with experience in metal-oxide semiconductor (MOS) random logic and circuit design. He also had the crucial knowledge of the new silicon gate process technology with self-aligned gates, which he had created at Fairchild in 1968. At Fairchild in 1968, Faggin also designed and manufactured the world's first commercial IC using SGT, the Fairchild 3708  that was featured on the cover of Electronics (Sept. 29, 1969). As soon as he joined the Intel MOS Department he created a new random logic design methodology based on silicon gate, and contributed many technology and circuit design inventions that enabled their single chip microprocessor to become a reality. His methodology set the design style for all the early Intel microprocessors and later for the Zilog Z80. He also led the MCS-4 project and was responsible for its successful outcome (1970–1971). Marcian "Ted" Hoff, head of the Application Research Department, contributed the architectural proposal for Busicom working with Stanley Mazor in 1969, then he moved on to other projects. When asked where he got the ideas for the architecture of the first microprocessor, Hoff related that Plessey, "a British tractor company", had donated a minicomputer to Stanford, and he had "played with it some" while he was there. Shima designed the Busicom calculator firmware and assisted Faggin during the first six months of the implementation. The manager of Intel's MOS Design Department was Leslie L. Vadász. At the time of the MCS-4 development, Vadasz's attention was completely focused on the mainstream business of semiconductor memories and he left the leadership and the management of the MCS-4 project to Faggin.
Busicom had designed their own special-purpose LSI chipset for use in their Busicom 141-PF calculator with integrated printer. They based their design on the architecture of the Olivetti Programma 101, the world's first tabletop programmable calculator, which Olivetti introduced in 1965. Busicom commissioned Intel to develop their design for production. Like the Olivetti Programma 101, the Busicom design used serial read-write memory. The Busicom memory was based on MOS shift registers rather than the costly Olivetti memory based on magnetostriction wire.
Intel determined the Busicom design was too complex, since serial memories required more components, and would use 40 pins, a packaging standard different from Intel's own 16-pin standard. Intel proposed to develop a new design which could be produced with standard 16-pin DIP packaging, and would have a reduced instruction set. The memory simplification would come from using Intel's newly developed dynamic RAM memory. This new design was the 4004 chip, which is one of a set of 4 chips, along with ROM, DRAM, and serial-to-parallel shift register chips. The 4004 was subsequently designed by Federico Faggin  using silicon gate technology and built of approximately 2,300 transistors and was followed the next year by the first ever 8-bit microprocessor, the 3,500 transistor 8008 (and the 4040, a revised and improved 4004). It was not until the development of the 40-pin 8080 in 1974, a project conceived and directed by Faggin  that the address and data buses would be separated, giving faster and simpler access to memory.
The 4004 employs a 10 µm process silicon-gate enhancement load pMOS technology on a 12 mm² die and can execute approximately 92,000 instructions per second; a single instruction cycle is 10.8 microseconds. The original clock rate design goal was 1 MHz, the same as the IBM 1620 Model I.
The Intel 4004 was designed by physically cutting sheets of Rubylith into thin strips to lay out the circuits to be printed, a process made obsolete by current computer graphic design capabilities.
For the purpose of testing the produced chips, Faggin developed a tester for silicon wafers of MCS-4 family that was itself driven by 4004 chip. The tester also served as a proof for the management that Intel 4004 microprocessor could be used not only in calculator-like products, but also for control applications.
Name and variants
When Faggin designed the MCS-4 family, he also christened the chips with distinct names: 4001, 4002, 4003, and 4004, breaking away from the numbering scheme used by Intel at that time which would have required the names 1302, 1105, 1507, and 1202 respectively. Had he followed Intel's number sequence, the idea that the chips were part of a family of components intended to work seamlessly together would have been lost. Intel's early numbering scheme for integrated circuits 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 of the number were used to indicate the sequential number in the development of the component. The 8008 microprocessor was originally called 1201, per Intel's naming conventions. Before its market introduction, the 1201 was renamed 8008, following the new naming convention started with the 4001/2/3/4.
Tadashi Sasaki attributes the basic invention to break the calculator into four parts with ROM (4001), RAM (4002), shift registers (4003) and CPU (4004) 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 Robert Noyce from Intel, leading up to the Busicom deal.
The 4004 is part of the MCS-4 family of LSI chips that can be used to build digital computers with varying amounts of memory. The other members of the MCS-4 family are memories and input/output circuits, which are necessary to implement a complete computer. The 4001 is a ROM (read-only memory) with four lines of output; the 4002 is a RAM (random access memory) with four lines of input/output. The 4003 is a static shift register to be used for expanding the I/O lines; e.g., for keyboard scanning or controlling a printer.
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). The RAM and ROM parts were also unusual in their integration of output (and, in the ROMs, input) ports that significantly reduced the minimum part count in an MCS-4 system, but required inclusion of a certain amount of processor-like logic on the chips themselves to accept, decode and execute relatively high-level data transfer instructions.
The standard arrangement for a 4004 system is anything up to 16 x 4001 ROM chips (in a single bank) and 16 x 4002 RAM chips (in four banks of four), which together provide the 4KB program storage, 1024 + 256 nibbles of data/status storage, plus 64 output and 64 input/output external data/control lines (which can themselves be used to operate, e.g. a 4003). 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.
|Intel 4004 registers|
- Maximum clock rate is 740 kHz. The 4004 had this maximum clock rating upon its initial 1971 release[Note 1]
- Instruction cycle time: minimum 10.8 µs (8 clock cycles / machine cycle)
- Instruction execution time 1 or 2 machine cycles (10.8 or 21.6 µs), 46250 to 92500 instructions per second.
- Adding two 8-digit numbers (32 bits each, assuming 4-bit BCD digits) takes a claimed 850 µs, or approximately 79 machine cycles (632 clock ticks), for an average of just under 10 cycles (80 ticks) per digit pair and an operating speed of 1176 x 8-digit additions per second[Note 2]
- Separate program and data storage. Contrary to Harvard architecture designs, however, which use separate buses, the 4004, with its need to keep pin count down, uses a single multiplexed 4-bit bus for transferring:
- 12-bit addresses
- 8-bit instructions
- 4-bit data words
- Able to directly address 5120 bits (equivalent to 640 bytes) of RAM, stored as 1280 4-bit "characters" and organised into groups representing 1024 "data" and 256 "status" characters (512 and 128 bytes).[Note 3]
- Able to directly address 32,768 bits of ROM, equivalent to and arranged as 4096 8-bit words (i.e. bytes).[Note 4]
- Instruction set contained 46 instructions (of which 41 were 8 bits wide and 5 were 16 bits wide)
- Register set contains 16 registers of 4 bits each
- Internal subroutine stack, 3 levels deep.
- 4001: 256-byte ROM (256 8-bit program instructions), and one built-in 4-bit I/O port. A 4001 ROM+I/O chip cannot be used in a system along with a 4008/4009 pair.
- 4002: 40-byte RAM (80 4-bit data words), and one built-in 4-bit output port; the RAM portion of the chip is organized into four "registers" of 20 4-bit words:
- 4003: 10-bit parallel output shift register for scanning keyboards, displays, printers, etc.
- 4008: 8-bit address latch for access to standard memory chips, and one built-in 4-bit chip select and I/O port
- 4009: program and I/O access converter to standard memory and I/O chips
- 4269: keyboard/display interface
- 4289: memory interface (combined functions of 4008 and 4009)
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 x 4-bit or 8 x 8-bit characters (or a mixture) of working RAM, nor for simple interface chips thanks to the ROM's built-in I/O lines. However, as project complexity increases, the various other support chips start to become useful.
Numerous versions of the Intel MCS-4 line of processors were produced. 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". The next generation of the chips was plain white ceramic (also marked C), and then dark grey ceramic (D). Many of the more recent versions of MCS-4 family were also produced with plastic (P).
The first commercial product to use a microprocessor was the Busicom calculator 141-PF. The 4004 was also used in the first microprocessor-controlled pinball game, a prototype produced by Dave Nutting Associates for Bally in 1974.
Here are my opinions from [the] study [I conducted for the patent case]. The first microprocessor in a commercial product was the Four Phase Systems AL1. The first commercially available (sold as a component) microprocessor was the 4004 from Intel.— 
A popular myth has it that Pioneer 10, the first spacecraft to leave the solar system, used an Intel 4004 microprocessor. According to Dr. Larry Lasher of Ames Research Center, the Pioneer team did evaluate the 4004, but decided it was too new at the time to include in any of the Pioneer projects. The myth was repeated by Federico Faggin himself in a lecture for the Computer History Museum in 2006.
Legacy and value
Federico Faggin signed the 4004 with his initials because he knew that his silicon gate design embodied "the essence of the microprocessor". In a corner of the die you can read "F.F."
On November 15, 2006, the 35th anniversary of the 4004, Intel celebrated by releasing the chip's schematics, mask works, and user manual. A fully functional 41 x 58 cm, 130x scale replica of the Intel 4004 was built using discrete transistors and put on display in 2006 at the Intel Museum in Santa Clara, California.
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