♦ The History of the Microprocessor Michael R. Betker, John S. Fernando, and Shaun P. Whalen Invented in 1971, the microprocessor evolved from the inventions of the transistor (1947) and the integrated circuit (1958). Essentially a computer on a chip, it is the most advanced application of the transistor. The influence of the microprocessor today is well known, but in 1971 the effect the microprocessor would have on every- day life was a vision beyond even those who created it. This paper presents the his- tory of the microprocessor in the context of the technology and applications that drove its continued advancements. Introduction The microprocessor, which evolved from the The history of the microprocessor can be divided inventions of the transistor and the integrated circuit into five stages: (IC), is today an icon of the information age. The per- • The birth of the microprocessor, vasiveness of the microprocessor in this age goes far • The first microcomputers, beyond the wildest imagination at the time of the first • A leading role for the microprocessor, microprocessor. From the fastest computers to the • The promise of reduced instruction set com- simplest toys, the microprocessor continues to find puter (RISC), and new applications. • Microprocessors of the 1990s. The microprocessor today represents the most These five stages define a rough chronology, with complex application of the transistor, with well over some overlap. Each stage could be said to reflect a 10 million transistors on some of the most powerful generation of microprocessors, with corresponding microprocessors. In fact, throughout its history, the generations of applications. For each stage, we discuss microprocessor has always pushed the technology of representative microprocessors and their key applica- the day. The desire for ever-increasing performance tions. Figure 1 shows a timeline of the development has led to the rapid improvements in technology that of the microprocessor, starting with the Intel* 4004. have enabled more complex microprocessors. The information in this paper was taken from Advances in IC fabrication processes, computer archi- many sources, including other overviews of the his- tecture, and design methodologies have all been tory of the microprocessor.1,2,3,4 We have selected the required to create the microprocessor of today. microprocessors discussed in this paper based on their As we trace the history of the microprocessor, innovation and their success in the marketplace. we will explore its evolution and the driving Embedded processors are given limited coverage since, forces behind this evolution. In the earliest in many cases, the microprocessors mentioned in stages, microprocessors filled the needs of embed- more detail have led to versions for embedded applica- ded applications. It was not long, however, tions. We have not covered digital signal processors before advances in microprocessors and comput- (DSPs), even though they could be considered a type ers drove the capabilities and needs of both. We of microprocessor. However, we have included in the will discuss these and other forces behind the appendix of the paper a history of microprocessors at history of the microprocessor, including the Bell Labs, which has designed microprocessors since impact of individuals and companies. the latter half of the 1970s. Copyright 1997. Lucent Technologies Inc. All rights reserved. Bell Labs Technical Journal N Autumn 1997 29 The Birth of the Microprocessor “Announcing a New Era of Integrated Electronics” Panel 1. Acronyms, Abbreviations, and Terms —Headline, Intel 4004 ad The history of the microprocessor begins with the ARM—Advanced RISC Machines birth of the Intel 4004, the first commercially available BiCMOS—bipolar complementary metal-oxide semiconductor microprocessor (see Panel2). The roots of this devel- BIOS—basic input/output system opment can be traced directly back to the inventors of BIU—bus interface unit the transistor. In 1955, William Shockley founded CISC—complex instruction set computer Shockley Semiconductor in Palo Alto, California CMOS—complementary metal-oxide semicon- (arguably the birth of Silicon Valley). This company ductor (with n- and p-type transistors) eventually employed Gordon Moore and Robert CPI—cycles per instruction CP/M—control program/monitor Noyce, who left with others to form Fairchild CPP—communications protocol processor Semiconductor in 1957. While at Fairchild, Noyce CPU—central processing unit played a significant role in the development of the IC, CTC—Computer Terminal Corporation first commercially available in 1961. In 1968, Moore DEC—Digital Equipment Corporation and Noyce left Fairchild to form Intel Corporation. DMA—direct memory access Intel’s focus at that time was the development of mem- DRAM—dynamic random access memory ory chips, but Intel’s history was forever changed by DSP—digital signal processor EU—execution unit the events leading to the development of the 4004 for FPU—floating-point unit the Busicom calculator company. The first fully func- GaAs—gallium arsenide tional 4004 parts were available in March 1971, with GUI—graphical user interface the first public announcement in November 1971. IC—integrated circuit Around the same time Intel developers began IEEE—Institute of Electrical and Electronics working on the 4004, they also began work on the Engineers I/O—input/output 1201 project for Computer Terminal Corporation MIPS—millions of instructions per second (CTC). The 1201 was intended to be a single metal- MIPS—microprocessor without interlocking pipe oxide semiconductor (MOS) chip that would replace a stages similar processor designed using medium-scale- MMU—memory management unit integration components. The 1201 was later renamed MOS—metal-oxide semiconductor the Intel 8008. The 8008 was the first 8-bit micro- MPEG—Motion Picture Experts Group MSI—medium-scale integration processor and laid the foundation for future micro- NMOS—MOS with n-type transistors processors from Intel. The 8008 was designed in OS—operating system 10-micron PMOS (metal-oxide semiconductor using PC—personal computer p-type transistors) technology, and required approxi- PMOS—MOS with p-type transistors mately 3,500 transistors. The die for the 8008 mea- RAM—random access memory sured 4.9 mm 36.7 mm. The 8008 was packaged in RISC—reduced instruction set computer ROM—read only memory an 18-pin dual inline package, ran at 200 kHz, and SC/MP—single-chip microprocessor was capable of 60,000 instructions per second. SCP—Seattle Computer Products While the 8008 was being developed, a June 1971 SPICE—simulation program integrated circuit Texas Instruments (TI) advertisement in Electronics emphasis magazine showing a “Computer On A Chip” revealed SRAM—static random access memory that CTC had also contracted with TI to produce a chip TI—Texas Instruments similar to the 8008. This presented a difficult situation VLIW—very long instruction word VLSI—very large scale integration for Intel, which had not yet announced the 4004 and presumed it was ahead of the competition. As it 30 Bell LabsTechnical Journal ◆Autumn 1997 TMS1000 TMS9900 16032 32332 32032 32532 Other SC/MP 6502 R2000 R3000 R4000 R8000 R10000 MIPS PA7100 PA7200 PA8000 HP DEC 21064 21164 21264 endor V Zilog Z80 Z8000 Z80000 Sparc RISC I RISC II Sparc Super Ultra Sparc Sparc 68060 Motorola 6800 68000 68020 68030 68040 PPC601 PPC604 88100 Pentium Pentium Intel 8008 8080 8086 80286 386 486 Pentium 4004 Pro II 1970 1975 1980 1985 1990 1995 2000 Year DEC – Digital Equipment Corporation HP – Hewlett-Packard RISC – Reduced instruction set computer SC/MP – Single-chip microprocessor Figure 1. Microprocessor timeline. turned out, the TI chip was not operational. TI sor. In 1969, prior to either TI’s or Intel’s micro- dropped the project when CTC decided not to use processor efforts, an engineer named Gilbert Hyatt either the 8008 or the TI chip. filed for a patent6 that covered a computer on a sin- The architecture of the 8008 was based on the gle integrated chip. Twenty-one years later, when the existing CTC processor and had a single 8-bit accumu- patent was finally awarded, it would cause a great lator (A), along with six general-purpose 8-bit registers deal of turmoil and legal action. (B, C, D, E, H, and L). It supported a 14-bit address In Search of Applications and included logical operations and interrupts. The The first commercially available microprocessors, 8008 was designed to interface with standard memory the Intel 4004 and 8008, were developed with specific chips. Information on the 8008 was publicly available applications in mind. The 4004 was intended for an as early as December 1971, followed by the official electronic calculator, and the 8008 was designed for a introduction in April 1972. computer terminal. They were intended to replace a A significant result of TI’s efforts was a 1971 number of smaller devices wired together to perform patent application,5 which in 1978 resulted in the the desired function. Beyond their original applica- first patent issue covering a microprocessor. Intel tions, it was unclear what the market was for these never applied for a patent covering the microproces- first microprocessors. Bell Labs Technical Journal ◆ Autumn 1997 31 Panel 2. Intel 4004, The Birth of an Age19,20 Bob Noyce and Gordon Moore left Fairchild agreement was reached to build the proposed Semiconductor Corporation in 1968 and founded Intel chip set. Intel Corporation for the express purpose of pro- Intel was now committed, but neither Hoff nor ducing proprietary memory products. However, Mazor had ever designed chips and they realized as in most start-up companies, there was a that the complexity of these chips would require desire, for cash flow reasons, to do a certain someone with extensive experience. The design amount of custom work. It was thought that cus- languished for three months, with the customer tom products would ramp up to volume produc- getting increasingly concerned about the sched- tion faster than would proprietary products.