Chip History from 1970 to Today - Semiconductor Memory and the Rise of the Microprocessor
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The birth of the commercially available microprocessor occurred in 1971 when semiconductor memory maker Intel released a four bit PMOS technology microcontroller called the 4004. The 4004 was originally developed for use in a calculator, but when that project fell through, Intel released it for sale on the open market. Among the companion chips for the 4004 were a 256 byte ROM for program storage (up to 16 chips for a maximum program size of 4K) and a 40 byte RAM for data storage (organized as 80 4 bit data words). The 4004 had 16 registers of 4 bits each for internal data storage.
Shortly after the 4004, Intel introduced an 8 bit processor in 1972, the 8008. These were followed by improved versions in 1974 - the 4 bit 4040 and the 8 bit 8080 (which used NMOS technology like most of its direct competitors). The 8080 was used in early hobbyist computers like the Altair 8800 (for which Bill Gates wrote a version of BASIC at the beginning of his career) and the IMSAI 8080. By 1976 the 16 bit era was legitimized by Intel's introduction of the 8086, to be followed in 1979 by the 8088 used in the original IBM Personal Computer.
The 8088 was internally an 8086 design, but with an 8 bit bus which allowed the use of cheaper pre-existing 8 bit peripheral components. The initial version of the 8086 was built in HMOS technology (an enhanced NMOS process), but later versions of this processor and most others switched to CMOS technology as that process matured. Other factors contributing to the switch were the increasing issues of power consumption and heat dissipation as more transistors running at higher clock speeds got packed into the same silicon chip real estate.
As microprocessors improved over time, semiconductor memory components also doubled their capacity approximately every two years in accordance with Moore's Law while continuing to improve in performance as well. The original IBM PC was introduced with 16K bytes of dynamic semiconductor RAM for common program/data storage (expandable to 64K bytes via empty sockets on the motherboard).
Intel didn't have a monopoly on commercial 8 bit microprocessors for long. In the mid-1970s other contenders were released, including Motorola's 6800, Zilog's Z80, Mostek's 6502, and RCA's COSMAC 1802 (an early CMOS technology microprocessor). The Z80 and 6502 in particular found there way into many of the popular new 8-bit personal computers of the time including the Apple II, Radio Shack's TRS-80, Commodore PET, and the Atari series.
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