Microprocessor chronology

1970s.
The first microprocessors were designed and manufactured in the 1970s. Designers predominantly used MOSFET transistors with pMOS logic in the early 1970s, and then predominantly used NMOS logic from the mid-1970s. They also experimented with various word lengths. Early on, 4-bit processors were common (e.g. Intel 4004). Later in the decade, 8-bit processors such as the MOS 6502 superseded the 4-bit chips. 16-bit processors emerged by the decade's end. Some unusual word lengths were tried, including 12-bit and 20-bit. Intel's 4004 is widely regarded as the first commercial microprocessor.
1980s.
In the 1980s, 16-bit and 32-bit microprocessors were common among new designs, and CMOS technology overtook NMOS. Transistor count increased dramatically during the decade.
Key home computers which remained popular for much of the 1980s predominantly use processors developed in the 1970s. Versions of the MOS Technology 6502, first released in 1975, power the Commodore 64, Apple IIe, BBC Micro, and Atari 8-bit family. The Zilog Z80 (1976) is at the core of the ZX Spectrum.
The IBM PC launched in 1981 with an Intel 8088. It was not until Intel's 80286 (used in the 1984 IBM PC/AT), and later the 80386, that processors designed in the 1980s drove the computers of the 1980s. These chips had higher clock speeds and 32-bit memory access. The end of the decade saw the launch of the Intel 80486, the first personal computer CPU with on-chip floating point support instead of as an optional coprocessor.
A mid-1980s generation of GUI-driven home computers is based around the Motorola 68000: Macintosh (1984), Atari ST (1985), Amiga (1985), and X68000 (1987). Even the Sega Genesis game console, released in 1988-89, uses a 68000 as the main CPU and a Z80 for sound.
1990s.
The 32-bit microprocessor dominated the consumer market in the 1990s. Processor clock speeds increased by more than tenfold between 1990 and 1999, and 64-bit processors began to emerge later in the decade. In the 1990s, microprocessors no longer used the same clock speed for the processor and the RAM. Processors began to have a front-side bus (FSB) clock speed used in communication with RAM and other components. Typically, the processor itself ran at a clock speed that was a multiple of the FSB clock speed. Intel's Pentium III, for example, had an internal clock speed of 450–600 MHz and an FSB speed of 100–133 MHz. Only the processor's internal clock speed is shown here.
2000s.
64-bit processors became mainstream in the 2000s. Microprocessor clock speeds reached a ceiling because of the "heat dissipation barrier". Instead of implementing expensive and impractical cooling systems, manufacturers turned to parallel computing in the form of the multi-core processor. Overclocking had its roots in the 1990s, but came into its own in the 2000s. Off-the-shelf cooling systems designed for overclocked processors became common, and the gaming PC had its advent as well. Over the decade, transistor counts increased by about an order of magnitude, a trend continued from previous decades. Process sizes decreased about fourfold, from 180 nm to 45 nm.