Evolution of the Microprocessor

The Intel Corporation is generally acknowledged as the company that introduced the
first microprocessor successfully into the marketplace. Its first processor, the 4004, was
introduced in 197 1 and evolved from a development effort while making a calculator chip
set. The 4004 microprocessor was the central component in the chip set, which was called
the MCS-4. The other components in the set were a 4001 ROM, a 4002 RAM, and a 4003
shift register.

Shortly after the 4004 appeared in the commercial marketplace, three other
general-purpose microprocessors were introduced: the Rockwell International 4-bit PPS-4,
the Intel 8-bit 8008, and the National Semiconductor 16-bit IMP-16. Other companies,
such as General Electric, RCA, and Viatron, also made contributions to the development of
the microprocessor prior to 197 1.The microprocessors introduced between 197 1 and 1972 were the first-generation systems designed using PMOS technology. In 1973, second-generation microprocessors such as the Motorola 6800 and the Intel 8080 (8-bit microprocessors) were introduced.The second-generation microprocessors were designed using NMOS technology. This
technology resulted in a significant increase in instruction execution speed over PMOS and
higher chip densities. Since then, microprocessors have been fabricated using a variety of
technologies and design.

NMOS microprocessors such as the Intel 8085, the Zilog 280,
and the Motorola 6800/6809 were introduced based on second-generation microprocessors.
A third generation HMOs microprocessor, introduced in 1978 is typically represented by
the Intel 8086 and the Motorola 68000, which are 16-bit microprocessors.
During the 1980’s, fourth-generation HCMOS and BICMOS (a combination of
bipolar and HCMOS) 32-bit microprocessors evolved. Intel introduced the first commercial
32-bit microprocessor, the problematic Intel 432, which was eventually discontinued.
Since 1985, more 32-bit microprocessors have been introduced. These include Motorola’s
68020, 68030, 68040, 68060, PowerPC, Intel’s 80386, 80486, the Intel Pentium family,
Core Duo, and Core2 Duo microprocessors..

The performance offered by the 32-bit microprocessor is more comparable to
that of superminicomputers such as Digital Equipment Corporation’s VAX11/750 and
VAX11/780. Intel and Motorola also introduced RISC microprocessors: the Intel 80960
and Motorola 88 100/PowerPC, which had simplified instruction sets. Note that the purpose
of RISC microprocessors is to maximize speed by reducing clock cycles per instruction.
Almost all computations can be obtained from a simple instruction set. Note that, in order
to enhance performance significantly, Intel Pentium Pro and other succeeding members of
the Pentium family and Motorola 68060 are designed using a combination of RISC and
CISC.of the Motorola 68XXX and PowerPC microprocessors will
be provided next. Motorola’s 32-bit microprocessors based on the 68000 (16-bit
microprocessor) architecture include the MC68020, MC68030, MC68040, and MC68060.
Table 1.1 compares the basic features of some of these microprocessors with the 68000.
MC68020 is Motorola’s first 32-bit microprocessor. The design of the 68020 is
based on the 68000. The 68020 can perform a normal read or write cycle in 3 clock cycles
without wait states as compared to the 68000, which completes a read or write operation in
4 clock cycles without wait states. As far as the addressing modes are concerned, the 68020
includes new modes beyond those of the 68000. Some of these modes are scaled indexing,
larger displacements, and memory indirection.