No matter how smart you are, you wouldn’t know anything if you couldn’t remember. Thoughts and ideas would go in one neuron and out another, forever lost in the entropy of the universe. You know things because you can call back thoughts and ideas, to work on them again or just talk about them. A computer, too, needs some way of retaining its thoughts. Like you, it needs both short-term memory for holding ideas while it works on them and long-term memory to store all the facts and old ideas that, by chance, it might need another day.

The short-term memory of computers is often called simply memory. The long-term memory is often termed mass storage and involves several technologies. Hard disk drives hold the ideas you put into the computer, both commercial programs and your own original data. Floppy disks and optical drives (CDs and DVDs for the most part) store the ideas of others than you want your computer to access. Tape drives provide a safety net, keeping a duplicate copy of your computer’s most important ideas.

Memory

Just as you need your hands and workbench to hold tools and raw materials to make things, your computer’s microprocessor needs a place to hold the data it works on and the tools to do its work. Memory, which is often described by the more specific term RAM (which means Random Access Memory), serves as the microprocessor’s workbench. The amount and architecture of the memory of a system determines how it can be programmed and, to some extent, the level of complexity of the problems it can work on. Modern software often requires that you install a specific minimum of memory—a minimum measured in megabytes—to execute properly. With modern operating systems, more memory often equates to faster overall system performance.

In today’s computers, memory usually comes in subassemblies called memory modules that plug into special sockets on the main circuit board of your computer. Most computers have three or more of these sockets in a group, one or more of which is filled with a memory module as standard equipment.

Hard Disk Drives

Long-term memory is where you store thoughts and ideas that, although you don’t need them immediately, you need to know—stuff like your shoe size, which doesn’t come up in everyday conversation (at least not among normal adults) but becomes a handy factoid when musing through a mail-order catalog. Your computer’s hard disk holds such factoids along with all the other stuff it needs to know but not at this exact moment—such as the instructions for programs you’re not using, financial records you hope the auditor will ignore, term papers you someday hope to publish as best-selling fiction, and even extra designs for wallpaper for your computer screen. Your computer’s hard disk lets you call on any of those stored facts on a microsecond’s notice.

Most hard disks take the form of a sealed box, typically silver and black with a green circuit board dotted with tiny electrical components on the bottom. A hard disk connects to the main circuit board of your computer through that interface we talked about earlier via a short, wide, and flat set of wires, called a ribbon cable because it looks like a ribbon (although an admittedly strange gray ribbed ribbon).

Floppy Disk Drives

Once upon a time, some computers lacked hard disk drives and instead used floppy disk drives (”once upon a time” being in the unbelievable past, a little before Cinderella cleaned out fireplaces). Inexpensive, exchangeable, and technically unchallenging, the floppy disk served as a data interchange system for years because it was based on well-proven technologies and was mass produced by the millions.

Today, the floppy disk drive is found on nearly every computer, but functionally it’s about as useful to your computer as an appendix. (Granted, an appendix won’t fit into a drive slot, but you get the idea.) In today’s world the floppy disk is slow and holds too little information, so it is gradually disappearing from computers, replaced in function by any of a variety of optical drives.

The computers that still have floppy disk drives usually wear them proudly, out in front. On desktop systems, it’s usually the uppermost drive in the case. From the outside you see only a long, black slot about three-and-a-half inches wide with a rectangular button near one corner. Notebook computers put their floppy disk drives, if they have one, wherever they fit—usually hidden in the side of the computer under the keyboard.

Optical Drives

Getting new memories into your computer is the primary job served by optical drives. They store programs and data in a convenient form—small discs—that’s standardized so that you can exchange the discs (and memories) between computers. (Note that due to a strange quirk of design and origin, magnetic drives use “disks” whereas optical drives use “discs.”)

Optical discs currently come in two flavors: Compact Discs and Digital Versatile Discs. These are the CDs and DVDs you slide into your home entertainment system. In either form, discs are cheap and easy to copy, so software publishers have made the CD-ROM their preferred means of getting their products to you, with DVDs slowly replacing CD-ROMs because of their higher capacity. You can create your own optical disks with a suitable drive to store either data for your computer or music and video for your entertainment systems.

A CD-ROM or DVD drive is usually the other drive on the front of your desktop computer, bigger than the floppy and featuring a volume control and headphone jack (should you want to slide a music CD into the drive). You’ll know what it is as soon as you press the eject button and the tray rolls out. On a notebook computer, manufacturers stuff their optical drives wherever they fit, usually on the side near the back of the computer.

Tape Drives

Tape is for backup, pure and simple. It provides an inexpensive place to put your data just in case—just in case some light-fingered freelancer decides to separate your computer from your desktop; just in case the fire department hoses to death everything in your office that the fire and smoke failed to destroy; just in case you empty your Recycle Bin moments before discovering you accidentally deleted all your exculpatory tax records; just in case an errant asteroid ambles through your roof. Having an extra copy of your important data helps you recover from such disasters as well as those that are even less likely to happen.

Tape drives are optional on personal computers. They add enough cost that people would rather risk their data. On larger computers (the servers used in business), tape drives are more common because the cost of restoring data is so high, probably thousands of times the cost of a drive, that their use is justified.

The real useful work that computers do involves not just you but also the outside world. Your computer must be able to communicate to put its intelligence to work. When your computer communicates with other systems far away, the process is often called telecommunications. When your computer connects with other computers over a network, engineers call the communication capability connectivity. When your computer plugs into printers and other nearby peripherals, engineers say your computer is doing what it’s supposed to—there’s no fancy word for it. No matter. Thanks to the communication capabilities of your computer, it can link to any of a number of hardware peripherals through its network jacks and input/output ports. Better still, through modems and the Internet, it can connect with nearly any computer in the world.

Expansion Buses

Computers need to communicate with any of a number of peripherals, some of which reside inside the computer’s case. The primary link to these internal components is the expansion bus.

As the name implies, the expansion bus of a computer allows you to expand its capabilities by sliding in accessory boards (cleverly termed expansion boards). For this to work, the expansion bus sets up an internal communication channel inside your computer. Expansion slots are spaces inside the computer that provide special sockets or connectors to plug in the capabilities and functions locked in the circuitry of the expansion boards.

In a desktop computer, the expansion bus usually is a row of three or more long connectors on the main circuit board near the back of the computer’s case. Depending on the overall design of the computer, one or more of these slots will be filled with expansion boards in the basic factory configuration. In a notebook computer, expansion slots are different, meant to accept modules the size of credit cards that deliver the same functions as expansion boards.

Interfaces

Interfaces provide a communication channel that lets your computer exchange information with a variety of devices, primarily storage systems (discussed later in the chapter). The interface translates the signals inside your computer into a form that’s more suited to traveling outside the confines of its main circuit boards. You’ve probably heard people speak about the most familiar interfaces, such as ATA (also called IDE) and SCSI, acronyms that describe connections used by hard and optical disk drives.

The interface takes the form of a connector. The ATA interface is usually built in to the main circuit board of all modern computers. A cable links this connector to one on a disk drive. The SCSI interface usually resides on a separate circuit board that fits into the expansion bus of your computer.

Input/Output Ports

Your computer links to its peripherals through its input and output ports. Every computer needs some way of acquiring information and putting it to work. Input/output ports are the primary routes for this information exchange.

In the past, the standard equipment of most computers was simple and almost preordained—one serial port and one parallel port, typically as part of their motherboard circuitry. Modern standards are phasing out these ports, so we’ll consider them (for purposes of this book) legacy ports. Today, new and wonderful port standards are proliferating faster than dandelions in a new lawn. Hard-wired serial connections are moving to the new Universal Serial Bus (USB), whereas the Infrared Data Association (IrDA) system and oddly named Bluetooth provide wireless links. Digital video connections use FireWire, also called IEEE 1394. Even the simple parallel port has become an external expansion bus capable of linking dozens of devices to a single jack.

The ports are the jacks or connectors you’ll find on the back of most desktop computers or scattered around the edges of notebook machines. They come in various sizes and shapes, meant to match special connectors unambiguously.

Local Area Networks

Any time you link two or more computers together, you’ve created a network. Keep the machines all in one place—one home, one business, one site in today’s jargon—and you have a local area network (LAN). Spread them across the country, world, or universe with telephone, cable, or satellite links and you get a wide area network (WAN). A network is both a wiring system and a software system. The wires connect computers together; the software is the language for passing messages around.

Most networks use some kind of wire to connect computers, although wireles networks are becoming popular, especially in homes where their short range is no problem and their lack of wires a great advantage.

Telecommunications

To extend the reach of your computer beyond your home or office, you usually must rely on the international telephone system to provide the connection. Because short-sighted engineers a hundred years ago never considered that you’d want to connect your computer to your telephone, they built the phone system to use an entirely different kind of signal than your computer uses. Consequently, when you want to connect with other computers and information sources such as the Internet through the international telephone system, you need a modem to adapt your computer’s data to a form compatible with the telephone system’s.

In a quest for faster transfers than the ancient technology of the classic telephone circuit can provide, however, data communications are shifting to newer systems, including digital telephone services (such as DSL), high-speed cable connections, and direct digital links with satellites. Each of these requires its own variety of connecting device—not strictly speaking a “modem” but called that for consistency’s sake. Which you need depends on the speed you want and the connections available to you.

Internet

The Internet is properly described as a “network of networks.” In concept, it links all the computers in the world together so that they can share information (but more often games and pornography). The World Wide Web is essentially the commercial side of the Internet. Once you link up with the Web, your computer is no longer merely the box on your desk. It becomes part of a single, massive international computer system with a single goal: transferring money out of your bank account. Even so, it retains all the features and abilities you expect from a computer—an Internet connection only makes it even more powerful.

The Internet is more an idea than a physical form. Picture it as a spider web anchored to each and every computer in the world.

The function that defines the computer is its ability to calculate and make decisions. Without the ability to make decisions, a computer could not follow a program more complex than a simple sequence. If your computer lacked the ability to calculate, you might as well have a footstool next to your desk or a dumbbell in your briefcase. These abilities give the computer its electronic thinking power—or more importantly, help the computer enhance your own thinking power.

Several components make up the thinking function of a computer. The most important is the microprocessor, but by itself a microprocessor couldn’t function. It would be like a brain without a spine and blood supply. For the computer, such support functions are handled by a chipset. In addition, the computer needs the equivalent of instinct in animals and humans, the primitive behaviors that help it survive even without learning. For the computer, the equivalent of instinct is the BIOS, a set of factory-installed, essentially unchangeable programs that give the computer its basic functions and, some say, personality.

Microprocessor

The most important of the electronic components on the motherboard is the microprocessor. It does the actual thinking inside the computer. The power of a computer—how fast it can accomplish a given job, such as resizing a digital photo—depends on the model of microprocessor inside the computer as well as how fast that microprocessor operates (the speed is measured in the familiar megahertz or gigahertz). The kind of microprocessor also determines what software language it understands. For example, Windows computers and Macintosh computers use microprocessors from different families that understand different software languages.

As fits its role, the microprocessor usually is the largest single integrated circuit in a computer. It makes more connections, so it has the biggest socket and usually holds the dominant position on the main circuit board. It is the centerpiece of every computer. In fact, the microprocessor is the most complicated device yet devised by human beings, so complex that earlier designs couldn’t fit all the silicon microcircuitry into a single chip. Many older microprocessors (such as the Pentium II series) were modules that combined several smaller integrated circuit chips into a big assembly that included a main microprocessor, a coprocessor, a cache controller, and cache memory. Today, however, everything for an advanced microprocessor such as the Pentium 4 fits on a single silicon chip about one-inch square.

Chipset

The chipset of a computer provides vital support functions to its microprocessor. The chipset creates signals that are the lifeblood of the microprocessor, such as the clock or oscillator that sets the pace of its logic operations. In addition, the chipset links the microprocessor to the rest of the computer, both the memory and external functions, through input/output ports. The chipset also provides the vital link to your computer’s expansion bus that enables you to add new capabilities to its repertory. The chipset is so important that in most computers it affects the performance and operation of the system as much as does its microprocessor. In fact, for some knowledgeable buyers, the choice of chipset is a major purchasing criterion that distinguishes one computer from another.

At one time, a chipset was a collection of dozens of individual electronic components. In today’s computers, however, manufacturers have combined all the traditional functions of this essential support circuitry into a few large integrated circuits. In computers, in fact, the entire chipset has been squeezed into a single package. Typically the integrated circuit or circuits that make up the chipset are squares of black epoxy sitting on the main computer circuit board, usually the largest individual electronic components there, except for the microprocessor.

BIOS

Just as animals rely on instincts to survive in the real world before they can learn from their experiences, a computer has a built-in program that tells it what to do before you load any software. This program is called the Basic Input/Output System because it tells the computer’s microprocessor how to get input from the outside world and send output there. The BIOS defines how a computer acts and behaves before you load software. In modern computers, the BIOS has several additional functions, all essential to making the computers get started and work.

Unlike the microprocessor and chipset, the BIOS is mostly ephemeral: It is a program, a list of software codes. It takes physical form because it permanently resides in a special kind of memory chip, one that retains its memory without the need for electricity. This way, the BIOS program is always remembered, ready to be used as soon as the computer gets switched on. The chip holding the BIOS typically is a large flash memory chip. Its most distinguishing feature is its label, however. Because it holds software, the BIOS chip is usually emblazoned with a copyright notice just like other software products.

In today’s world and using today’s technology, a computer is an electronic device that uses digital logic under the direction of a program for carrying out calculations and making decisions based on those calculations. By this essential definition, a computer has four elements to its construction: electronics, digital logic, programming, and calculating/decision-making.

That’s a mouthful of a definition, and one that’s pretty hard to swallow, at least in one piece. To help you understand what all this means, let’s take a closer look at each of the elements of this definition.

Electronics

The technology that makes the circuits of a computer work is called electronics. Dig into this word, and you’ll find that it comes from electrons, the lightweight particles carrying a negative charge that comprise one of the fundamental constituents of atoms. The flow of electrons through metals is what we normally think of as electricity, a word taken from the Greek word for amber, elektrum. Static electricity, the stuff that creates sparks when you touch a metal doorknob after shuffling across a carpet on a dry winter day, was once most readily produced by rubbing amber with a silk cloth. So, the stuff that makes computers work is named after what’s essentially petrified pine tree sap.

Electronics is a technology that alters the flow of charges through electrical circuits. In the more than two centuries since Benjamin Franklin started toying with kites and keys, scientists have learned how to use electricity to do all sorts of useful things, with two of the most important being to operate motors and burn light bulbs. Motors can use electricity to move and change real-world objects. Lights not only help you see but also see what an electrical circuit is doing.

For the record, this electricity stuff is essential for building a computer. Babbage showed how it could be done with cams, levers, gears, and an old crank (which might have been Babbage himself). If you, like Babbage, have too much time on your hands, you could build a computer for yourself that runs hydraulically or with steam. In fact, scientists hope to build computers that toy with quantum states.

However, electricity and electronics have several big advantages for running a computer over nearly everything else (except that quantum stuff, and that’s why scientists are interested in it). Electricity moves quickly, at nearly the speed of light. Electrical devices are easy to interface with (or connect to) the real world. Think of those motors and electric lights. They operate in the real world, and an electrical computer can change the currents that run these motors and lights. Moreover, engineers have mastered the fabrication of electrical circuits of all sizes, down to those so small you can’t see them, even if you can see the results of their work on your computer screen. And above all, electrical circuits are familiar with off-the-shelf parts readily available, so you can easily tinker with electrical devices and build them economically. And that’s the bottom line. Just as celebrities are famous primarily for being famous, electronics are used a lot because they are used a lot.

Digital

Most of the circuits inside a computer use a special subset of electronic technology called digital electronics. The most important characteristic of the digital signals in these circuits is that they usually have only two states, which are most often described as on and off (or one and zero). Some special digital systems have more than two states, but they are more than you need to understand right now.

Usually the states are defined as the difference between two voltage levels, typically zero and some standard voltage, or between a positive and negative voltage value. The important part about the states of digital electronics is not what they are but what is between them—nothing. Certainly you can find a whole world of numbers between zero and one—fractions come to mind—but with digital technology the important fact is not whether there could be something between the digital states, but that anything other than the two digital states gets completely ignored. In essence, digital technology says if something is not a zero it is a one. It cannot be anything else.

Think about it, defining the world this way could make sense. For example, an object is either a horse or it is not a horse. Take a close look. It has hooves, four legs, a mane, and a tail, so you call it a horse. If it has six legs and a horny shell and, by the way, you just stepped on it, it is probably not a horse. Yes, we could get on sketchy ground with things such as horseflies, but nit-picking like that is just noise, which is exactly what the two digital states ignore.

This noise-free either/or design is what makes digital technology so important. Noise is normally a problem with electrical signals. The little bit of electricity in the air leaks into the electrical signals flowing through wires. The unwanted signal becomes noise, something that interferes with the signal you want to use. With enough noise, the signal becomes unusable. Think of trying to converse over the telephone with a television playing in the background. At some point, turning the TV up too much makes it impossible to hold a phone conversation. The noise level is simply too high.

Digital signals, however, allow circuits to ignore the noise. For computers, that’s wonderful, because every little bit of added noise could confuse results. Adding two plus two would equal four plus some noise—perhaps just a little, but a little might be the difference between being solvent and having your checking account overdrawn. Noise-free digital technology helps ensure the accuracy of computer calculations.

But sometimes things can get tricky. Say you encounter a beast with hooves, four legs, a mane, a tail, and black-and-white stripes. That’s a horse of a different color—a creature that most zoologists would call a zebra and spend hours telling you why it’s not a horse. The lesson here (besides being careful about befriending didactic zoologists) is that how you define the difference between the two digital states is critical. You have to draw the line somewhere. Once you do—that is, once you decide whether a zebra is a horse or not—it fits the two-state binary logic system.

Logic

Logic is what we use to make sense of digital technology. Logic is a way of solving problems, so you can consider it a way of thinking. For computers, “logically” describes exactly how they think. Computers use a special system of logic that defines rules for making decisions based, roughly, on the same sort of deductive reasoning used by Sherlock Holmes, some great Greek philosophers, and even you (although you might not be aware of it—and might not always use it).

Traditional logic uses combinations of statements to reach a conclusion. Here is an example of logical reasoning:

1) Dragons eat people.
2) I am a people.
3) There is a dragon waiting outside my door.

Conclusion: If I go outside, I will be eaten.

This sort of reasoning works even when you believe more in superstition than science, as the example shows.

Computer circuitry is designed to follow the rules of a formal logic system and will always follow the rules exactly. That’s one reason why people sometimes believe computers are infallible. But computers make no judgments about whether the statements they operate on are true or false. As long as they get logically consistent statements (that is, the statements don’t contradict one another), they will reach the correct conclusions those statements imply.

Computers are not like editors, who question the content of the information they are given. To a computer, proposition 1, “Dragons eat people,” is accepted unquestioningly. Computers don’t consider whether a race of vegetarian dragons might be running about.

Computers don’t judge the information they process because they don’t really process information. They process symbols represented by electrical signals. People translate information into symbols that computers can process. The process of translation can be long and difficult. You do some of it by typing, and you know how hard that is—translating thoughts into words, then words into keystrokes.

Computers work logically on the symbols. For the computer, these symbols take electronic form. After all, electrical signals are the only things that they can deal with. Some symbols indicate the dragon, for example. They are the data. Other symbols indicate what to do with the data—the logical operations to carry out. All are represented electronically inside the computer.

Engineers figured out ways of shifting much of the translation work from you to the computer. Consequently, most of the processing power of a computer is used to translate information from one form to another, from something compatible with human beings into an electronic form that can be processed by the logic of the computer. Yes, someone has to write logic to make the translation—and that’s what computer programming is all about.

Programmability

A computer is programmable, which means that it follows a program. A program is a set of instructions that tells the computer how to carry out a specific task. In that way, a program is like a recipe for chocolate chip cookies (a metaphor we’ll visit again) that tells, step by step, how to mix ingredients together and then burn the cookies.

Programmability is important because it determines what a computer does. Change the program the computer follows, and it will start performing a new, different task. The function of the computer is consequently determined by the program.

That’s how computers differ from nearly all machines that came before them. Other machines are designed for a specific purpose: A car carries you from here to there; an electric drill makes holes in boards and whatever else gets in the way; a toaster makes toast from bread. But a computer? It can be a film editor, a dictation machine, a sound recorder, or a simple calculator. The program tells it what to do.

Calculating and Decision-Making

The real work that goes on inside your computer bears no resemblance to what you ask it to do. Programs translate human-oriented tasks into what the computer actually does. And what the computer does is amazingly simple: It reacts to and changes patterns of bits, data, and logic symbols.

Most of the time the bit-patterns the computer deals with represent numbers. In fact, any pattern of binary bits—the digital ones and zeroes that are the computer’s fodder—translates directly into a binary number. The computer manipulates these bit-patterns or binary numbers to come up with its answers. In effect, it is calculating with binary numbers.

The computer’s calculations involve addition, subtraction, multiplication, division, and a number of other operations you wouldn’t consider arithmetic, such as logic operations (and, or, and not) and strange tasks such as moving bits in a binary code left and right.

More importantly, the computer can compare two binary codes and do something based on that comparison. In effect, it decides whether one code is bigger (or smaller, or whatever) than another code and acts on that decision.

Work your way up through this discussion, and you’ll see that those codes aren’t necessarily numbers. They could be translations of human concerns and problems—or just translations of letters of the alphabet. In any case, the computer can decide what to do with the results, even if it doesn’t understand the ideas behind the symbols it manipulates.

The whole of the operation of the computer is simply one decision after another, one operation after another, as instructed by the computer’s program, which is a translation of human ideas into a logic system that uses binary code that can be carried out by electronic signals.

So what is a computer? You have one answer—one that more than anything else tells you that there is no easy answer to what a computer is.

Biomechanical engineers are changing the way people think about insect intelligence. In an effort to develop machines that walk like insects, they have discovered that form doesn’t dictate function, and function doesn’t dictate form. The two are intimately linked.

Although some researchers have worked hard to develop machines that walk like insects by adding more and more intelligence, others have gone back to the drawing board with a more mechanical approach. By mimicking the structure of the insect body, they have been able to make mechanical insects that duplicate the gait of your typical six-legged bug. These mechanical insects can even change their gait and crawl over obstacles, all using no more intelligence than an electric motor. In other words, biomechanical engineers have discovered that the intelligence is in the design, not the insect.

Comparing the thinking power of the 12 neurons in an insect’s brain with the power of a computer becomes a question of design. The insect is designed for eating garbage and buzzing around your head. Although you might feed your computer a diet of garbage, it’s really designed for executing programs that calculate answers for you, thus letting you communicate and otherwise waste your time. Any comparison between bug and computer is necessarily unfair. It must inevitably put one or the other on alien turf. The computer is easily outclassed by anything that walks, but walking bugs won’t help you solve crossword puzzles.

With that perspective, you can begin to see the problems with comparing computer and human intelligence. Although they sometimes perform the same tasks—for example, playing chess—they have wildly different designs. A human can forage in the jungle (African or Manhattan), whereas a computer can only sit around and rust. A computer can turn one pixel on your monitor green at 7:15 a.m. on August 15, 2012, whereas you might not even bother waking up for the event.

Computers earn our awe because they can calculate faster and remember better. Even the most complex computer applications—video games, photo editors, and digital animators—all reduce down to these two capabilities.

Calculating involves making decisions and following instructions. People are able to and often do both, so comparing computers to people is only natural. However, whereas it might take you 10 minutes to decide between chocolate and vanilla, a computer makes a decision in about a billionth of a second. If you had to make all the decisions your computer does to load a copy of Microsoft Windows, multicellular organisms could evolve, rise up from the sea, mutate into dinosaurs and human beings, and then grow wings and fly to nearby planets before you finished. So it stands to reason that computers are smarter, right?

As with insects, the playing field is not quite level. Your decision isn’t as simple as it looks. It’s not a single issue: Your stomach is clamoring for chocolate, but your brain knows that with just one taste, a zit will grow on your nose and make you look like a rhinoceros. And there are those other flavors to tempt you, too. You might just have several billion conflicts to resolve before you can select a cone, plain or sugar, and fill it full of…did you want ice cream or frozen yogurt, by the way?

No doubt some of us follow instructions better than others. Computers, on the other hand, can’t help but follow their instructions. They are much better at it, patiently going through the list step by step. But again, that doesn’t make them smarter than you. On the contrary, if you follow instructions to the letter, you’re apt to end up in trouble. Say you’ve found the map to Blackbeard’s treasure, and you stand, shovel in hand, at the lip of a precipice. If the map says to take 10 paces forward, you’re smart enough to know better. A computer confronted with the same sort of problem would plummet from its own digital precipice. It doesn’t look ahead (well, some new machines have a limited ability to sneak a peek at coming instructions), and it doesn’t know enough to stop short of trouble.

Computers have excellent memory. But unlike a person, a computer’s memory isn’t relational. Try to remember the name of an old friend, and you might race through every name you know in alphabetical order. Or you might remember he had big ears, and instantly the name “Ross” might pop into your mind. You’ve related your friend’s name with a distinguishing feature.

By itself, a computer’s memory is more like a carved stone tablet—permanent, unchanging, and exacting. A computer has to know precisely what it’s looking for in order to find it. For example, a computer can find a record of your 2002 adjusted gross income quite easily, but it can’t come up with Ross’s name based on the fact that he has big ears. On the other hand, you, as a mere human, have about zero chance of remembering the 2002 adjusted gross incomes of 10,000 people—something even a 10-year-old personal computer can tackle adroitly.

The point is not to call either you or your computer dumb but rather to make you see the differences in the way you both work. The computer’s capabilities compliment your own. That’s what makes them so wonderfully useful. They can’t compete with people in the brain function department, except in the imaginations of science fiction writers.

The glitz is gone. Computers no longer rule Hollywood. Robots and aliens (and alien robots in particular) are now the big villains set to rule the world. Businesses no longer seek the fastest computers but instead strive for slowness—that is, slowing down the time between buying and replacing machines.

Computers are now as disposable as old newspaper. We all have one—or will soon. But their advantages hark back to Babbage’s claims for his unrealized Analytical Engine. They are accurate, error-free, fast, and cheap—particularly when you compare using a computer for calculations with doing the same work by hand. Got an aspirin?

The one claim that we won’t award to the modern computer is being smarter than human calculators. Computers aren’t smarter than you are, even if one can balance a checkbook and you can’t. Certainly the computer has a better head for numbers than you do. After all, computers are specifically designed to work with numbers. For people, numbers are—at best—an afterthought, at least if you’re not an accountant. People have bigger worries, such as finding food, shelter, and sex. Computers have us to take care of those details for them (maybe not the sex) so that they can concentrate on calculating.

Computers are good at calculating—and they’re fast. Even today’s cheapest personal computers can figure the product of two 40-bit numbers billions of times in the fraction of a second it takes one of us human beings even to realize we have two 40-bit numbers to multiply.

Scientists and engineers like to make comparisons between the intelligence of their computers (usually the fastest computer ever built, which changes month to month) and the thinking ability of animate creatures, typically something like “an insect brain.” Most scientists know it’s all balderdash, but they make these claims because it gets them big headlines. No mere bug can multiply two 40-bit numbers—or even wants to.

Computers are more accurate because they are designed that way. Using digital logic, their thinking automatically wipes out any noise that can confuse their calculations. By elaborating on the math with error-checking, they can quickly detect and prevent most mistakes. They don’t think at all like you and I do. They have to be told exactly what to do, led by the hand through the process of finding an answer by a set of instructions we call a program.

Computers also have better memories than people. Again, they are designed that way. One of our human advantages is that we can adapt and shift the way we deal with things thanks to our malleable memories. Remember Mom’s cooking? Computers have long-term memories designed for just the opposite purpose—to remember everything, down to the last detail, without error and without limit. Even Deep Blue, the computer that finally beat a flesh-and-blood chess Grand Master, would quickly succumb to the elements if left outside. Although able to calculate billions of chess moves in seconds, it lacks the human sense to come in out of the rain. And the feet.

What we call “computer intelligence” is something far different from what we call “intelligence” in humans. That’s actually good, because even experts can’t agree on what human intelligence is, or even how humans think. Things are much more straightforward for computers. We know how they think as well as how to measure how well they do their jobs.

Strictly speaking, a computer is something that computes, which is not a particularly informative definition. In the vagueness of the term, however, you’ll find an interesting bit of history. The word computer does not necessarily mean an electronic machine or a machine at all. If you were a researcher a hundred years ago and you wanted to take a break from heavy-duty math work, such as creating a tide table, you might have taken your computer out to lunch. Scientists engaged in difficult mathematics often employed a bevy of computers—men and women with pencils, papers, and green eye-shades who computed the numbers they needed.

Up until the end of World War II, a computer was a person who computed. She might use a pencil (a pen if she were particularly confident of her results), a slide rule, or even a mechanical calculator. Poke a few numbers in, pull a crank, and the calculator machine printed an answer in purple ink on paper tape—at least if the questions involved simple arithmetic, such as addition. If this person did a lot of calculations, the black ink of the numbers soon faded to a pale gray, and he grew calluses on his fingertips and cranking hand.

The early machines for mathematics were once all known as calculators, no matter how elaborate—and they could be quite elaborate. Charles Babbage, a 19th-century English country gentleman with a bold idea and too much time on his hands, conceived the idea of a machine that would replace the human computers used to calculate values in navigational tables. Babbage foresaw his mechanical computer-replacement as having three advantages over number-crunchers who wielded pencil and paper: The machine would eliminate mistakes, it would be faster, and it would be cheaper. He was right about all but the last, and for that reason he never saw the most intricate machines he designed actually built. Moreover, he never called his unbuilt machines “computers.” His names for them were the Difference Engine and the Analytical Engine. Even though Babbage’s machines are considered the forerunners of today’s computers—sometimes even considered the first computers by people who believe they know such things—they really weren’t known as “computers” in Babbage’s time. The word was still reserved for the humans who actually did the work.

The word computer was first applied to machines after electricity replaced blood as the working medium inside them. In the early part of the 20th century, researchers struggled with the same sort of problems as those in Babbage’s time, and they solved them the same way. In the 10 years from 1937 to 1947, scientists created the first devices that are classed as true computers, starting with an electrically powered mechanical machine and ending with an all-electronic device powered by an immense number of vacuum tubes, which required an equally immense amount of good fortune for them to all work long enough to carry out a calculation. Nobody called them computers just yet, however.

The first of these machines—a mechanical computer of which Babbage would have been proud—was the IBM-financed Automatic Sequence Controlled Calculator, which is often called Harvard Mark I. The five-ton design included 750,000 parts, including switches, relays, and rotating shafts and clutches. It stretched out for 50 feet and was eight feet tall. It sounded, according to an observer of the time, like a roomful of ladies knitting.

Many of the fundamentals of today’s computers first took form in the partly electronic, partly mechanical machine devised by John Vincent Atanasoff at Iowa State College (now University). His ideas and a prototype built with the aid of graduate student Clifford Berry have become a legend known as the Atanasoff Berry Computer (with the acronym ABC), the first electronic digital computer—although it was never contemporaneously called a “computer.” Iowa State called the device “the world’s fastest calculator” as late as 1942.

In Britain, crypto-analysts developed a vacuum-tube (valve in Britain) device they called Colossus that some people now call the first electronic computer—usually British folk who don’t want you to forget that the English can be clever, too. But the rest of the world never called Colossus a computer—or anything else—because it was top secret until the end of the century.

The present usage of the word computer goes back only to June 5, 1943, when ENIAC (the most complex vacuum tube-based device ever made) was first proposed as a collaboration between the United States Army and the University of Pennsylvania. The original agreement on that date first used the description that became its name, as well as the name for all subsequent machines: the Electronic Numerical Integrator and Computer.

Three years and $486,804.22 later, the machine made its first computation at the university. The 30-ton behemoth, and its offspring, captured the imagination of the world, and the term computer shifted from flesh-and-blood human calculators to machines. In Hollywood, such thinking machines grew even bigger and took over the world, at least in 1950s science fiction movies. In business, ENIAC’s offspring, the Univac, took over billing for utilities and gave a new name to bookkeeping foul-ups and bureaucratic incompetence: computer error. Also, scientists tried to figure out how to squeeze a room-sized computer into a space capsule, into which they could barely shoehorn a space-suited human being.

The scientists pretty much figured things out—they created the microprocessor, which led to the age of microcircuits—but not until after a few scientific diversions, including sending men to the moon. Oddly enough, although modern microelectronic circuitry is credited as an offshoot of the space program (shrinking things down and making them lighter was important to an industry in which lifting each ounce cost thousands of dollars), in the history of technology, the moon landing (1969) comes two years before the invention of the microprocessor (1971).

In framing a shot, the only image you need to see displayed on the LCD view panel on the back of your camera is a full-screen look through the lens. For the review of photos you’ve previously captured, however, most digital cameras offer additional modes. Some of these include single-image mode, multiple-image mode, slideshow mode, and zoom mode.

Single Image

In single-image mode, that’s all you see—a one-shot view. Most cameras will let you step through all the images you’ve exposed so that you can look at them one at a time. Although you can’t compare shots (except in your mind), you will see the greatest possible level of detail. Single-image mode is the basic viewing mode for digital cameras in review mode, and usually the only preview view.

Multiple Image

In multiple-image mode—sometimes called thumbnail mode—your camera breaks its viewfinder into a matrix of individual images, typically an array of four or nine. Although each image is a fraction of its individual size (say one-quarter or one-ninth), this mode allows you to make side-by-side comparisons. You can pick out an image to keep or trash in one quick glance. This mode is particularly useful when you urgently need more memory and want to eliminate wasted shots to gain memory space.

Slideshow

Long before we had home videos to bore our friends and neighbors through wintry evenings, God gave us the slideshow. You’d drag out a rolled-up screen that never properly unrolled, plug in the projector, and flash side after slide, one at a time, on the screen. The slideshow mode of a digital camera’s electronic viewfinder operates similarly, a one-after-another display of the images in its memory. This mode allows you to briefly view all the photos you’ve captured before deciding to chuck them all and start over.

The slideshow lets you assess the mass of your work in full detail. At that, it can be quite useful in making a quick evaluation of your technical prowess. As with the presentation of single images, it does not allow you to make quick comparisons.

Zoom

The small screen and low pixel count in digital camera LCD displays can make checking image details difficult. Consequently, many cameras incorporate an electronic zoom mode in their viewfinder systems. Typically this mode will let the LCD panel display one pixel for each pixel in the captured image, which magnifies the image by a factor of two to four. Although you cannot see the entire image at one time, you can usually pan across its width and height to check each pixel. If you’re critical about the images you take, you’ll want zoom mode. For ordinary snapshots, however, you may find it unnecessary and may not miss the feature in a camera that lacks it.

If you plan only to use your LCD panel to review images, you don’t much care about where it is on your camera. You can just tilt the camera to the viewing angle you prefer. If, however, you want to use the panel as a viewfinder, the mounting of the LCD is decidedly important. It must be located so you can view it conveniently while pointing the camera lens at your subject. Not all digital cameras have LCD panels that let you do this conveniently.

Adjustable panels allow you to swivel the LCD to whatever position is most comfortable for you to view it. In particular, you can tilt it upward so that it functions as a waist-level viewfinder, which many professional photographers prefer, particularly for portrait photography.