The microprocessor is 50 years old: It all started with the Intel 4004

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2300 transistors, 108 kilohertz clock frequency and 4-bit arithmetic unit: the modestly equipped Intel 4004 is the world’s first microprocessor on a single piece of silicon. Intel had developed it on behalf of the Japanese company Busicom, which used the 4004 in the 141-PF desktop computer from 1972.

In 1971, it was not foreseeable that the successors to the 4004 desktop processor – i.e. 8008, 8080 and 8086, but also, for example, the Zilog Z80 – would become the most important engines of the digital revolution. Even Silicon Valley, where Intel, AMD, Fairchild and HP were already located at the time, did not have its later significance by a long way.

The 4004 belonged to a chipset called MCS-4, which also consisted of the 2048-bit ROM component 4001, the RAM chip 4002 and the I / O component 4003. The main developers at Intel were Federico Faggin and Ted Hoff , Stan Mazor and Masatoshi Shima, who moved from Busicom to Intel in 1969.

At the time, not only Intel was working on the “microprocessor on a single chip” concept, but also Texas Instruments (TI) and some armaments companies. However, the Intel 4004 was ready in the summer of 1971, was – as mentioned at the beginning – advertised in November 1971 and was also used in the Busicom 141-PF.

Intel announced the 4004 in an ad in Electronic News magazine.

(Image: Intel)

Microprocessors existed before the Intel 4004 and the TI TMX 1795, just not combined on a single chip. But there were already logic ICs such as the well-known 74xx series, which TI had been producing since the 1960s. Such chips with “transistor-transistor logic” (TTL), which provide simple digital basic functions such as NAND gates, can be interconnected to form arithmetic units. But you needed a lot of them and the computer boards equipped with dozens of TTL chips were also called TTL graves.

In comparison, the single-chip microprocessors were not only more compact, they also consumed a lot less power. Due to the rapid development of chips and manufacturing technology, microprocessors quickly became faster or, with a similar range of functions, cheaper and more economical. The significantly more powerful 8-bit microprocessor Intel 8008 with 3500 transistors and 800 kHz appeared as early as the beginning of 1972.

The development of the microprocessor from the very beginning was anything but straightforward. Because Intel 4004 and 8008 could not be used flexibly enough for a long time. Federico Faggin and Masatoshi Shima therefore developed the 8080 with 6000 transistors at full speed until 1974.

Intel 4004 in DIL housing with 16 pins.

(Image: Intel)

As a result of the oil crisis, there was a recession in 1974, to which Intel also responded with restructuring. They didn’t fit Faggin. He left the company and founded the company Zilog in 1974 with Ralph Ungermann in Cupertino, not far from the Intel headquarters in Santa Clara. Masatoshi Shima followed later. By 1976, Zilog brought the Z80 onto the market, which was widely used from the Sinclair ZX80 to graphics-capable pocket calculators such as the TI-81.

Motorola introduced the 8-bit 6800 processor in 1974, which was based on the architecture of the PDP11 from Digital Equipment Corporation (DEC). The line continued in 1976 with the 6809 and 6801. Motorola 6801 with 35,000 transistors and the 6809 with 40,000 transistors played in higher leagues. The 6809 had a hardware multiplier. The instruction set architecture (ISA) was 16-bit throughout.

In the meantime, however, another “6800 descendant” had emerged, the similarly designed 6502 from MOS Technology. This is where Motorola developer Chuck Peddle had migrated. The 6502 was enormously popular, first in the Atari 800, Apple I, II, Commodore PET and VC-20, then later in 1982 in the form of the 6510 in the “bread box” C64.

However, in 1979 the successor to the 6800, the Motorola 68000, became particularly important. Its computing hardware (ALU) was only 16-bit, but the ISA and all registers already had trend-setting 32 bits. The linear address space was then a gigantic 4 GB, of which a huge 16 MB were initially still physically usable. Chief architect Skip Stritter had previously worked on the microprocessor for the IBM 370 mainframe computer, so that a number of ideas from the / 370 architecture were incorporated into the 68000.

In 1977, Intel improved the 8080 with the 8085 in response to the Z80. But by that time a 16-bit processor was already overdue, as the competition had it already finished or in the works. So Intel needed an inexpensive 8085 as quickly as possible, but it had been drilled to 16 bits – and the 8086 processor became that last resort.

Intel 8086 from 1978: 29,000 transistors with 3-micrometer structures, 5 MHz clock frequency

(Image: Intel)

The 8086, presented on June 4, 1978, inherited much of the 8085 and continued to fit in an inexpensive 40-pin DIL housing. In order to get by with a few external connections, however, a few tricks and contortions were necessary, some of which even years later drove programmers to despair. In order to save pins, address and data signals were not only switched to the same connections one after the other by multiplexing.

The 8086 was more of a 16-bit makeshift construction, but in the ancestor of all modern x86 PCs, the IBM PC, an even more trimmed 8086 version was used in 1981: the 8088 developed by Intel Israel in Haifa. Its most important The “advantage” was the reduced external data bus from 16 to 8 bits. This reduced performance, but the PC hardware required in addition to the microprocessor could be significantly simplified and set up more cheaply. It is well known that the IBM PC should not be particularly fast, but should at least be particularly cheap by IBM standards. That has changed immensely in the 40 years that have passed since then – but that’s a new story, that of the x86 PC.

More about the history of microprocessors:

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