The Microprocessor Today
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THE MICROPROCESSOR TODAY Michael Slater rom their humble beginnings 25 years communication tasks in multimedia PCs. ago, microprocessors have proliferat- Although the desktop computer market MicroDesign Resources Fed into an astounding range of chips, tends to discard old processors in just a few powering devices ranging from telephones years, many processors survive for an amaz- to supercomputers. Today, microprocessors ingly long time in the embedded market. for personal computers get widespread Personal computers have moved from 8- to attention—and have enabled Intel to 16-bit and now to 32-bit processors, and become the world’s largest semiconductor many workstations and servers are already maker. In addition, embedded micro- using 64-bit microprocessors. In the embed- processors are at the heart of a diverse range ded market, however, even 4-bit micro- of devices that have become staples of con- processors continue to sell well, and 8-bit sumers worldwide. devices lead in volume. Microprocessors have become specialized Figure 1 shows the changes in market in many ways. Those for desktop computers share for 32- and 64-bit microprocessors over fall into classes based on their instruction set the past five years. Driven by the success of architectures: either x86, the primary sur- the PC, the x86 architecture has dominated. viving complex instruction set computing Motorola’s 68000 has held a strong second- (CISC) architecture, or one of the five major place position in units (though not in dollars), reduced instruction set computing (RISC) with the embedded market as its stronghold. architectures—PA-RISC, Mips, Sparc, Alpha, Hitachi’s SuperH has come from nowhere to and PowerPC. Such chips typically integrate take third place, while other architectures few functions other than cache memory and have much more modest positions. As the bus interfaces with the processor but usual- dramatic changes during this period show, ly include a floating-point unit and memory market share can be quite turbulent among management unit. these second-tier embedded processors. Embedded microprocessors, on the other There are far more microprocessors avail- hand, typically do not have floating-point or able for sale today than it would be possible memory management units but often inte- to describe, even briefly, in an article such as grate various peripheral functions with the this. The current market includes more than 50 processor to reduce system cost. This makes surviving instruction set architectures, hun- them more application specific, leading to a dreds of different implementations, and thou- Microprocessor massive proliferation of devices character- sands of minor variations. Rather than ized not only by their processor’s instruction attempting to be comprehensive, I will focus Report’s publisher set and core CPU performance but also by on a selection of the leading-edge micro- their on-chip peripherals. processors and issues in each market segment. outlines technology Digital signal processors (DSPs) are the most specialized embedded microprocessors. Dividing up the market and business issues in Designed for real-time processing of digitized Microprocessors for personal computers analog signals, these processors have unique get the most public attention because the today’s instruction sets and other architectural features performance and compatibility of PCs that give them high performance for a rela- depend on the microprocessors at their microprocessor tively narrow range of tasks. Recently, a new cores. In recent years, PC microprocessors class of DSPs, called media processors, has have become so high profile that a bug of industry. emerged to handle audio, video, graphics, and minor significance in Intel’s Pentium proces- 32 IEEE Micro 0272-1732/96/$5.00 © 1996 IEEE sor captured headlines in the mainstream press for months. 70 x86 PowerPC Microprocessor commercials even appear on prime-time tele- 680x0 ARM vision. Embedded applications, on the other hand, have a 60 SuperH 29K fixed complement of software, so the microprocessor inside i960 Sparc is of relatively little interest to the consumer. Mips Alpha PC microprocessors are also a major profit area in the micro- 50 processor business. PCs are the only application so far that uses expensive microprocessors—typically costing $75 to 40 $500—in volumes of tens of millions per year. Embedded appli- cations use far more processors—literally billions per year—but most of them are very low cost devices, selling for under $5, 30 with thin profit margins. Some embedded applications use processors in the same price range as PCs, but they are very low volume—often only thousands of units per year. Today, Units shipped (millions) 20 even among 32-bit embedded processors, more than 60 chips sell for less than $40 and some for less than $10. 10 Microprocessors for PCs generate far more profit than embedded processors for two reasons. First, because the PC is the most expensive device to use a microprocessor in high volume, PC makers can afford more expensive processors. 0 When coupled with large amounts of DRAM, disk drives, 1991 1992 1993 1994 1995 and CRT displays that cost hundreds of dollars each, even a Year relatively expensive microprocessor does not dominate sys- tem cost. Second, the overwhelming importance of software Figure 1. Unit shipments of leading 32- and 64-bit archi- compatibility in the PC market has enabled Intel to achieve tectures. tremendous control over the PC microprocessor market. With no close competitors, Intel can enforce much higher profit margins than makers of embedded microprocessors, which designed for workstations. Because they are built in much must compete in a field where instruction set compatibility lower volumes than PC microprocessors, their amortized commands less value. design cost per unit is much greater. Such processors have Unix workstations constitute the high-performance segment survived primarily because they enable system businesses of the desktop computer market. (I use the term desktop com- that produce far more revenue (and profit) than would the puter as a shorthand for a single-user, general-purpose com- sale of a comparable number of microprocessors. This eco- puter; in this context, it includes deskside and portable systems nomic reality has led to large workstation makers designing as well as true desktops, workstations as well as PCs, and even nearly all of today’s workstation-specific microprocessors, many servers.) The workstation market has some of the same with chip companies playing little more than a foundry role. attributes as the PC market, in that application software com- As microprocessors for PCs have increased in speed, they patibility with previous-generation systems is of great impor- have reached a performance level that makes them suitable tance. There are two big differences, however. First, the total for much of the workstation market. This factor, combined Unix workstation market, in units, is less than 1% of the PC with the emergence of Microsoft’s Windows NT as a viable market, and second, performance is more important than alternative to Unix as a workstation operating system, is lead- price. As a result, microprocessors for workstations are typi- ing to a convergence of the technology for PCs with that for cally designed with performance as a higher priority than workstations. Ultimately, this convergence will threaten the price. survival of some of the workstation processor architectures. This digression into business issues is necessary for any com- prehensive discussion of the microprocessor industry, because The battle for the desktop these issues have a pervasive effect on microprocessor design Two operating systems account for the vast majority of desk- and manufacturing. Companies such as Intel and Motorola top computer use today: Microsoft Windows (in its various ver- fund leading-edge manufacturing plants for logic devices with sions) and Macintosh. IBM’s OS/2 is in third place, and Unix the high profits they make (or hope to make) supplying micro- is a distant fourth. Windows’ popularity has given Intel’s x86 processors for desktop computers. In contrast, makers of architecture a preeminent position, while the Macintosh has embedded processors generally get by with lower cost manu- established PowerPC as the only RISC architecture with a sig- facturing processes and depreciated fabrication plants. The nificant share of the desktop market. Even so, the Mac’s share divergent characters of the embedded and PC microprocessor is modest—around 8%—and shows no signs of increasing. markets also drives the evolution of instruction set architec- Nearly every maker of RISC microprocessors has dreamed tures: New architectures find relatively easy entry into the of capturing part of the x86 architecture’s high-volume mar- embedded market, while desktop processor makers go to great ket. The first to try was Sun, which hoped to repeat the PC lengths to stick with dominant architectures. industry phenomenon by making its Sparc-based worksta- Economics have had a huge effect on microprocessors tions, running Sun’s version of Unix, an openly licensed stan- December 1996 33 Current status Table 1. Originators and licensees for Digital plans to begin moving down into high-end PCs, setting leading desktop architectures. the stage for an eventual attack on the mainstream PC market. It is a long shot for Alpha to capture a significant mainstream Architecture Originator Licensees role, but at least it can’t be counted out yet. It is in this light that PowerPC’s position in the Windows NT Alpha Digital Semiconductor Mitsubishi, Samsung market appears so weak. PowerPC processors are not nearly Mips Mips Technologies IDT, NEC, Toshiba as fast as the Alpha chips and don’t offer a significant perfor- PA-RISC Hewlett-Packard Hitachi, Samsung mance advantage over Intel processors, leaving them between PowerPC Apple, IBM, Motorola Groupe Bull, Exponential a rock and a hard place. Customers looking for safety and com- Sparc Sun Microelectronics Fujitsu (includes HaL, patibility choose Intel; those seeking maximum performance ICL, and Ross) on a small set of applications are drawn to Alpha.