How A Computer Works

To be fair to Watson, computers have changed enormously in that time. In the 1940s, they were giantscientific and military behemoths commissioned by the government at acost of millions of dollars apiece; today, most computers are not evenrecognizable as such: they are embedded in everything from microwave ovens to cellphones and digitalradios. What makes computers flexible enough to work in all thesedifferent appliances? How come they are so phenomenally useful? And howexactly do they work? Let's take a closer look!

How a Computer Works

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Imagine if a computer were a person. Suppose you have a friend who'sreally good at math. She is so good that everyone she knows posts their math problems toher. Each morning, she goes to her letterbox and finds a pile ofnew math problems waiting for her attention. She piles them up on herdesk until shegets around to looking at them. Each afternoon, she takes a letter offthe top of the pile, studies the problem, works out thesolution, and scribbles the answer on the back. She putsthis in an envelope addressed to the person who sent her the originalproblem and sticks it in her out tray, ready to post. Then she moves tothe next letter in the pile. You can see that your friend is workingjust like a computer. Her letterbox is her input; the pile on her deskis her memory; her brain is the processor that works out the solutionsto the problems; and the out tray on her desk is her output.

Photo: Calculators and computers are very similar, because both work by processing numbers. However, a calculator simply figures out the results of calculations; and that's all it ever does. A computer stores complex sets of instructions called programs and uses them to do much more interesting things.

Suppose you're looking at a digital photo you just taken in a paint orphoto-editing program and you decide you want a mirror image of it (inother words, flip itfrom left to right). You probably know that the photo is made up ofmillions of individual pixels (colored squares) arranged in a gridpattern. The computer stores each pixel as a number, so taking adigitalphoto is really like an instant, orderly exercise in painting bynumbers! To flip a digital photo, the computer simply reverses thesequence of numbers so they run from right to left instead of left toright. Or suppose you want to make the photograph brighter. All youhaveto do is slide the little "brightness" icon. The computer then worksthrough all the pixels, increasing the brightness value for each oneby, say, 10 percent to make the entire image brighter. So, once again,the problem boils down to numbers and calculations.

What makes a computer different from a calculator is that it can workall by itself. You just give it your instructions (called a program)and off it goes, performing a long and complex series of operations allby itself. Back in the 1970s and 1980s, if you wanted a home computerto do almost anything at all, you had to write your own little programto do it. For example, before you could write a letter on a computer,you had to write a program that would read the letters you typed on thekeyboard, store them in the memory, and display them on the screen.Writing the program usually took more time than doing whatever itwas that you had originally wanted to do (writing the letter). Prettysoon, people started selling programs like word processors to save youthe need to write programs yourself.

Today, most computer users rely on prewritten programs likeMicrosoft Word and Excel or download apps for their tabletsand smartphones without caring much how they got there.(Apps, if you ever wondered, are just very neatly packaged computerprograms.) Hardly anyone writes programs any more,which is a shame, because it's great fun and a really useful skill. Most people see their computers as tools that help them do jobs, rather thancomplex electronic machines they have to pre-program.Some would say that's just as well, because most of us have better things to do than computerprogramming. Then again, if we all rely on computer programs and apps, someone has towrite them, and those skills need to survive. Thankfully, there's been a recentresurgence of interest in computer programming. "Coding"(an informal name for programming, since programs are sometimes referred to as "code")is being taught in schools again with the help of easy-to-use programminglanguages like Scratch. There's a growing hobbyist movement, linkedto build-it yourself gadgets like the Raspberry Pi and Arduino.And Code Clubs, where volunteers teach kids programming, are springing up all over the world.

Photo: Is this a computer... or not? Chess-playing machines like this werepopular in the 1970s. They worked exactly like computers using stored programs. But you couldn't change the program in any way or get these machines do anything other thanplay chess, so they weren't really examples of the kind of reprogrammable, general problem-solving machines that we mean when we're talking about "computers." By contrast, you can turn more or less any off-the-shelf modern computer (or smartphone) into a chess-playing computer just by loading a chessprogram or app. Photo by Marion S. Trikosko, US News & World Report Magazine Collection, courtesy ofUS Library of Congress.

Photo: Typical computer architecture: You can think of a computer as a series of layers, with the hardware atthe bottom, the BIOS connecting the hardware to the operating system, and the applications you actually use (such as word processors,Web browsers, and so on) running on top of that. Each of these layers is relatively independent so, for example, the same Windows operating system might run on laptops running a different BIOS, while a computer running Windows (or another operating system) can run any number of different applications.

That's the basic idea behind an operating system: it's the core software in a computer that (essentially) controls the basic chores of input, output, storage, and processing.You can think of an operating system as the "foundations" of the software in a computer that other programs (called applications) are built on top of. So a word processor and a chess game are two different applications that both rely on the operating system to carry out their basic input, output, and so on. The operating system relies on an even more fundamental piece of programming called the BIOS (Basic Input Output System), which is the link between the operating system software and the hardware. Unlike the operating system, which is the same from one computer to another, the BIOS does vary from machine to machine according to the precise hardware configuration and is usually written by the hardware manufacturer.The BIOS is not, strictly speaking, software: it's a program semi-permanently stored intoone of the computer's main chips, so it's known as firmware(it is usually designed so it can be updated occasionally, however).

Operating systems have another big benefit. Back in the 1970s (and early 1980s), virtually all computers were maddeningly different. They all ran in their own, idiosyncratic ways with fairly unique hardware (different processor chips, memory addresses, screen sizes and all the rest). Programs written for one machine (such as an Apple) usually wouldn't run on any other machine (such as an IBM) without quite extensive conversion. That was a big problem for programmers because it meant they had to rewrite all their programs each time they wanted to run them on different machines. How did operating systems help? If you have a standard operating system and you tweak it so it will work on any machine, all you have to do is write applications that work on the operating system. Then any application will work on any machine. The operating system that definitively made this breakthrough was, of course, Microsoft Windows, spawned by Bill Gates. (It's important to note that there were earlier operating systems too. You can read more of that story in our article on the history of computers.)

Although the mainboard can (theoretically) contain all the chips a computer needs, it's quite common for PCs to have three other separate circuit boards: one to manage networking, one to process graphics, and one to deal with sound.

PC makers tend to design and build their own motherboards, but most of the components they use are off-the-shelf and modular. So, for example, your Lenovo PC or Asus laptop might have a Toshiba hard drive, an Nvidia graphics card, a Realtek sound card, and so on. Even on the motherboard, the components may be modular and plug-and-play: "Intel Inside" means you've got an Intel processor sitting under the fan. All this means it's very easy to replace or upgrade the parts of a PC either when they wear out or grow obsolete; you don't have to throw the whole machine out. If you're interested in tinkering, there are a couple of good books listed in the "How computers work" section below that will walk you through the process.

You can connect your computer to peripherals (external gadgets like inkjet printers, webcams, and flash memory sticks)either with a wired connection (a serial or parallel cable) or with wireless (typically Bluetooth or Wi-Fi). Years ago, computers and peripheralsused a mind-boggling collection of different connectors for linkingto one another. These days, virtually all PCs usea standard way of connecting together called USB (universal serial bus). USB is meant to be "plug and play": whatever you plug into your computer works more or lessout of the box, though you might have to wait while your machine downloadsa driver (an extra piece of software that tells it how to use that particular piece of hardware).

Photo: USB ports on computers are very robust, but they do break from time to time, especially after years of use. If you have a laptop with a PCMCIA slot, you can simply slide in a USB adapter card like this to create two brand new USB ports (or to add two more ports if you're running short).

USB gives you much more connectivity than old-fashioned serial computer ports.It's designed so you can connect it in many different ways, either withone peripheral plugged into each of your USB sockets or using USB hubs(where one USB plug gives you access to a whole series of USB sockets, which can themselves have more hubs and sockets plugged into them).In theory, you can have 127 different USB devices attached to one computer. 041b061a72