Overview of Microprocessors

A musical greeting card has more computing power than the entire world did in 1950. Today even the cheapest microprocessor chips are more powerful than those big government computers from old science-fiction movies. A Palm Pilot is a better computer than the one in NASA's first lunar lander. Microprocessors have totally changed our society, culture, spending habits, and leisure time. They're incredibly cheap and ever-present and this trend shows no sign of letting up.

They're the peak, the top, the Mona Lisa. Microprocessors are the most complex, most expensive, and most innovative of all the semiconductors. They're also largely misunderstood, victims of mainstream journalism and stilted advertising claims. Of all the types of semiconductors we've covered in this book, microprocessors are the most likely to spark debate instead of yawns, both among engineers and normal people.

Microprocessors are called many things, so pick your favorite term. “Computer-on-a-chip” is much beloved by the popular press, and it's even partially correct. “Electronic brain” is another one. Microprocessors are essentially basic computer systems reduced to a single silicon chip. Microprocessors aren't exactly the same as computers, and the term will make engineers wince, but it's close enough for our purposes.

Central processing unit (CPU) and microprocessing (or microprocessor) unit (MPU) are technically accurate and interchangeable terms for microprocessors. Sometimes its name is shortened to “processor” and sometimes even just to “micro.” “Microcontroller” is also popular, although that term has slight shades of meaning to industry insiders and might not always be strictly accurate.

No matter what you call them, microprocessors sit at the top of the semiconductor hierarchy. Among engineers, designing microprocessors is a plum job, a career goal, and a primo adornment for your résumé. Manufacturing microprocessor chips is a status symbol among semiconductor companies, sometimes even a mark of national pride. “Real companies build microprocessors,” avowed one Silicon Valley chairman.

So just what are these things? Basically, microprocessors are chips that run software. If it runs a program, it's a microprocessor; if it doesn't, it's not. Microprocessors are the only type of chip that follows instructions. Those instructions, called either programs or software, might calculate equations, open garage doors, or zap space aliens on your TV screen. The biggest and fastest microprocessors run our computers, predict our weather, and guide our spacecraft.

Microprocessors are traditionally named with unfriendly and inscrutable four- or five-digit numbers. As with German sports cars, the model numbers are meaningful to the cognoscenti but are pretty meaningless to the rest of us. As an example, some popular microprocessors of the recent past are the 68000, the 80386, and the 29020. For the less technically inclined, these happen to be the processor chips inside the first Apple Macintosh, the IBM PCs of the early 1990s, and several Hewlett-Packard laser printers.

Microprocessor companies have recently started giving their chips made-up names, such as Pentium, Athlon, or UltraSPARC. These names are easier to remember than numbers, and when microprocessors and PCs started to become household products, that was an important marketing consideration. In Intel's case, the name Pentium was created to prevent rivals from making competitive chips with the same part number. It's easier to trademark “Pentium” than the number “80586.” (By the way, IBM attempted to trademark “/2” shortly after it created its PS/2 line of computers. Fortunately, the trademark office decided the number 2 was in the public domain.)

Microprocessors Everywhere

Every year the world's microprocessor vendors produce and sell about 10 billion microprocessor chips (give or take). That's well over one new microprocessor for every man, woman, and child living on Earth. Or if you prefer, that's about 35 microprocessors for every U.S. resident, every year

Who could possibly be consuming all these shiny new chips?

It's probably you. The average middle-class Western household contains about 30 to 40 microprocessors, including chips in the television, VCR, microwave oven, thermostat, garage-door opener, each remote control, washer, dryer, sprinkler timer, and a dozen other everyday items. The average car has about a dozen microprocessors; a 2001 Mercedes-Benz S-Class has 65. You might be carrying or wearing a number of microprocessors in your cellular telephone, pager, personal digital assistant (PDA), digital watch, electronic organizer, or wireless e-mail gadget.

Do you have a personal computer? It probably has a dozen different microprocessors in it, in addition to the big one you see in the advertisements. There are separate microprocessor chips for the floppy disk drive, the CD-ROM or DVD-ROM drive, the network, the modem, the graphics, the keyboard, the mouse, the monitor, and still more features that are buried inside. Microprocessors are everywhere and their ubiquity has changed our world.

As the chart in Figure 6.1 shows, microprocessor sales grew pretty steadily all through the decade of the 1990s. (Again, only a small fraction of this was because of the growth of PCs and other personal computers.) As you can see, the vast majority of microprocessors sold are low-end 8-bit processors (more about the nn-bits terminology later). Annual sales of microprocessors surpassed the world population back around 1995. Ever since then we've been effectively doubling the population of the world every year in new microprocessor chips.

The average selling price for microprocessor chips is about $5. There are a lot of low-end chips in that volume to make up for the few very expensive microprocessors that go into PCs. The vast majority of microprocessor chips do not go into PCs; they're used in everyday items and they are called embedded processors.

What Are Embedded Processors?

If you shout “microprocessor” in a crowded theater, most people will think of Pentium or of Intel, the company that manufactures the chip by that name. In fact, Intel and its Pentium processor line have become household names, an odd turn of events for such a technical product. Yet at no point in its history did Pentium ever have more than a 2 percent share of the microprocessor market. This is because only about 2 percent of the world's microprocessors are used in PCs at all. Even if Intel (or any other company) cornered the market for microprocessors powering personal computers, it would still only have about 2 percent of total world microprocessor volume.

The lion's share of the microprocessor market is called, oddly, the embedded market. Embedded in this sense means the chips are embedded into electronic products like an ancient insect embedded in amber. The metaphor is an odd one but unfortunately it has stuck. Engineers, managers, executives, and public relations professionals constantly have to explain, or apologize for, the “embedded” moniker.

It's also frustrating that the 98 percent of the market that's not involved in PCs should have to explain itself to the comparatively insignificant 2 percent that is. It's a bit like labeling the majority of the population “people who aren't astronauts.”

A somewhat more mellifluous description of embedded processors is “the invisible computer,” a term coined by Donald A. Norman in his 1998 book by the same name. As Norman pointed out, the embedded processors in our toys, games, and appliances have affected modern living conditions more than PCs.

What makes a microprocessor an embedded microprocessor? Nothing, other than the fact that it's not driving a PC. There is nothing technical or objective that separates an embedded processor from a nonembedded processor (i.e., one that drives a computer). Embedded processors are not faster or slower, cheaper or more expensive, or bigger or smaller than other microprocessors. PCs and Macintoshes have more than one microprocessor inside. One is famous and expensive; the others are embedded processors.

If there's nothing technically separating embedded and nonembedded (computer) processors, the difference is all a matter of context. Embedded describes how a chip is used, not the chip itself. Any microprocessor can be an embedded microprocessor if it's used that way. A single chip could occupy both camps. When Intel's 386 processor was giving way to newer PCs with the 486 chip, many engineers put 386 chips into embedded systems, a case where the 386 was both an embedded processor and a computer processor.