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When you mention the word "technology," most people think about computers. Virtually every facet of our lives has some computerized component. The appliances in our homes have microprocessors built into them, as do our televisions. Even our cars have a computer. But the computer that everyone thinks of first is typically the personal computer, or PC.

A PC is a general purpose tool built around a microprocessor. It has lots of different parts -- memory, a hard disk, a modem, etc. -- that work together. "General purpose" means that you can do many different things with a PC. You can use it to type documents, send e-mail, browse the Internet and play games.
In this article, we will talk about PCs in the general sense and all the different parts that go into them. You will learn about the various components and how they work together in a basic operating session. You'll also find out what the future may hold for these machines.
Let's take a look at the main components of a typical desktop computer.

• Central processing unit (CPU) - The microprocessor "brain" of the computer system is called the central processing unit. Everything that a computer does is overseen by the CPU.
• Memory - This is very fast storage used to hold data. It has to be fast because it connects directly to the microprocessor. There are several specific types of memory in a computer:
  
  
  
  • Random-access memory (RAM) - Used to temporarily store information that the computer is currently working with
  • Read-only memory (ROM) - A permanent type of memory storage used by the computer for important data that does not change
  • Basic input/output system (BIOS) - A type of ROM that is used by the computer to establish basic communication when the computer is first turned on
  • Caching - The storing of frequently used data in extremely fast RAM that connects directly to the CPU
  • Virtual memory - Space on a hard disk used to temporarily store data and swap it in and out of RAM as needed

Click on the various PC part labels to learn more about how they work.

Defining a PC Here is one way to think about it: A PC is a general-purpose information processing device. It can take information from a person (through the keyboard and mouse), from a device (like a floppy disk or CD) or from the network (through a modem or a network card) and process it. Once processed, the information is shown to the user (on the monitor), stored on a device (like a hard disk) or sent somewhere else on the network (back through the modem or network card). We have lots of special-purpose processors in our lives. An MP3 player is a specialized computer for processing MP3 files. A GPS is a specialized computer for handling GPS signals. A Nintendo DS is a specialized computer for handling games, but it can't do anything else. A PC can do it all because it is general-purpose.

• Motherboard - This is the main circuit board that all of the other internal components connect to. The CPU and memory are usually on the motherboard. Other systems may be found directly on the motherboard or connected to it through a secondary connection. For example, a sound card can be built into the motherboard or connected through PCI.
• Power supply - An electrical transformer regulates the electricity used by the computer.
• Hard disk - This is large-capacity permanent storage used to hold information such as programs and documents.
• Operating system - This is the basic software that allows the user to interface with the computer.
• Integrated Drive Electronics (IDE) Controller - This is the primary interface for the hard drive, CD-ROM and floppy disk drive.
• Peripheral Component Interconnect (PCI) Bus - The most common way to connect additional components to the computer, PCI uses a series of slots on the motherboard that PCI cards plug into.
• SCSI - Pronounced "scuzzy," the small computer system interface is a method of adding additional devices, such as hard drives or scanners, to the computer.
• AGP - Accelerated Graphics Port is a very high-speed connection used by the graphics card to interface with the computer.
• Sound card - This is used by the computer to record and play audio by converting analog sound into digital information and back again.
• Graphics card - This translates image data from the computer into a format that can be displayed by the monitor.

In the next section, we'll look at how your computer connects to the outside world.

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A typical computer connects to the world around it in three different ways: input/output devices, ports and networking. Input/Output
No matter how powerful the components inside your computer are, you need a way to interact with them. This interaction is called input/output (I/O). The most common types of I/O in PCs are:

• Monitor - The monitor is the primary device for displaying information from the computer.
• Keyboard - The keyboard is the primary device for entering information into the computer.
• Mouse - The mouse is the primary device for navigating and interacting with the computer
• Removable storage - Removable storage devices allow you to add new information to your computer very easily, as well as save information that you want to carry to a different location.
  
  
  
  
  • Floppy disk - The most common form of removable storage, floppy disks are extremely inexpensive and easy to save information to.
  • CD-ROM - CD-ROM (compact disc, read-only memory) is a popular form of distribution of commercial software. Many systems now offer CD-R (recordable) and CD-RW (rewritable), which can also record.
  • Flash memory - Based on a type of ROM called electrically erasable programmable read-only memory (EEPROM), Flash memory provides fast, permanent storage. CompactFlash, SmartMedia and PCMCIA cards are all types of Flash memory.
  • DVD-ROM - DVD-ROM (digital versatile disc, read-only memory) is similar to CD-ROM but is capable of holding much more information.

Ports

• Parallel - This port is commonly used to connect a printer.
• Serial - This port is typically used to connect an external modem.
• Universal Serial Bus (USB) - Quickly becoming the most popular external connection, USB ports offer power and versatility and are incredibly easy to use.
• FireWire (IEEE 1394) - FireWire is a very popular method of connecting digital-video devices, such as camcorders or digital cameras, to your computer.

Click on the various PC part labels to learn more about how they work.
Internet/Network

• Modem - This is the standard method of connecting to the Internet.
• Local area network (LAN) card - This is used by many computers, particularly those in an Ethernet office network, to connected to each other.
• Cable modem - This type of modem uses the cable TV system in your home to connect to the Internet.
• Digital Subscriber Line (DSL) modem - This is a high-speed connection that works over a standard telephone line.
• Very high bit-rate DSL (VDSL) modem - A newer variation of DSL, VDSL requires that your phone line have fiber-optic cables.

Now that you are familiar with the parts of a PC, let's see what happens in a typical computer session.
BIOS
A typical computer session begins with turning on the power. Here's what happens in that process:

1. You press the "On" button on the computer and the monitor.
2. You see the BIOS software doing its thing, called the power-on self-test (POST). On many machines, the BIOS displays text describing such data as the amount of memory installed in your computer and the type of hard disk you have. During this boot sequence, the BIOS does a remarkable amount of work to get your computer ready to run.
   
   
   
   
   • The BIOS determines whether the video card is operational. Most video cards have a miniature BIOS of their own that initializes the memory and graphics processor on the card. If they do not, there is usually video-driver information on another ROM on the motherboard that the BIOS can load.
   • The BIOS checks to see if this is a cold boot or a reboot. It does this by checking the value at memory address 0000:0472. A value of 1234h indicates a reboot, in which case the BIOS skips the rest of POST. Any other value is considered a cold boot.
   • If it is a cold boot, the BIOS verifies RAM by performing a read/write test of each memory address. It checks for a keyboard and a mouse. It looks for a PCI bus and, if it finds one, checks all the PCI cards. If the BIOS finds any errors during the POST, it notifies you with a series of beeps or a text message displayed on the screen. An error at this point is almost always a hardware problem.
   • The BIOS displays some details about your system. This typically includes information about the following:
     
     
     
     • Processor
     • Floppy and hard drive
     • Memory
     • BIOS revision and date
     • Display
   • Any special drivers, such as the ones for SCSI adapters, are loaded from the adapter and the BIOS displays the information.
   • The BIOS looks at the sequence of storage devices identified as boot devices in the CMOS Setup. "Boot" is short for "bootstrap," as in the old phrase "Lift yourself up by your bootstraps." Boot refers to the process of launching the operating system. The BIOS tries to initiate the boot sequence from the first device using the bootstrap loader.
   
   
   
   
   
   This animation walks you through a typical PC session.
   
3. The bootstrap loader loads the operating system into memory and allows it to begin operation. It does this by setting up the divisions of memory that hold the operating system, user information and applications. The bootstrap loader then establishes the data structures that are used to communicate within and between the sub-systems and applications of the computer. Finally, it turns control of the computer over to the operating system.

Once loaded, the operating system's tasks fall into six broad categories:

• Processor management - Breaking the tasks down into manageable chunks and prioritizing them before sending to the CPU
• Memory management - Coordinating the flow of data in and out of RAM and determining when virtual memory is necessary
• Device management - Providing an interface between each device connected to the computer, the CPU and applications
• Storage management - Directing where data will be stored permanently on hard drives and other forms of storage
• Application Interface - Providing a standard communications and data exchange between software programs and the computer
• User Interface - Providing a way for you to communicate and interact with the computer

Shopping for a new PC? Before you buy, check out the desktop computer reviews at Consumer Guide Products.

You open up a word processing program and type a letter, save it and then print it out. Several components work together to make this happen:

• The keyboard and mouse send your input to the operating system.
• The operating system determines that the word-processing program is the active program and accepts your input as data for that program.
• The word-processing program determines the format that the data is in and, via the operating system, stores it temporarily in RAM.
• Each instruction from the word-processing program is sent by the operating system to the CPU. These instructions are intertwined with instructions from other programs that the operating system is overseeing before being sent to the CPU.
• All this time, the operating system is steadily providing display information to the graphics card, directing what will be displayed on the monitor.
• When you choose to save the letter, the word-processing program sends a request to the operating system, which then provides a standard window for selecting where you wish to save the information and what you want to call it. Once you have chosen the name and file path, the operating system directs the data from RAM to the appropriate storage device.
• You click on "Print." The word-processing program sends a request to the operating system, which translates the data into a format the printer understands and directs the data from RAM to the appropriate port for the printer you requested.
• You open up a Web browser and check out HowStuffWorks. Once again, the operating system coordinates all of the action. This time, though, the computer receives input from another source, the Internet, as well as from you. The operating system seamlessly integrates all incoming and outgoing information.
• You close the Web browser and choose the "Shut Down" option.
• The operating system closes all programs that are currently active. If a program has unsaved information, you are given an opportunity to save it before closing the program.
• The operating system writes its current settings to a special configuration file so that it will boot up next time with the same settings.
• If the computer provides software control of power, then the operating system will completely turn off the computer when it finishes its own shut-down cycle. Otherwise, you will have to manually turn the power off.

We'll look at the future of PCs next.

EUVL Chipmaking
Silicon microprocessors have been the heart of the computing world for more than 40 years. In that time, microprocessor manufacturers have crammed more and more electronic devices onto microprocessors. In accordance with Moore's Law, the number of electronic devices put on a microprocessor has doubled every 18 months. Moore's Law is named after Intel founder Gordon Moore, who predicted in 1965 that microprocessors would double in complexity every two years. Many have predicted that Moore's Law will soon reach its end because of the physical limitations of silicon microprocessors. The current process used to pack more and more transistors onto a chip is called deep-ultraviolet lithography (DUVL), which is a photography-like technique that focuses light through lenses to carve circuit patterns on silicon wafers. DUVL will begin to reach its limit around 2005. At that time, chipmakers will have to look to other technologies to cram more transistors onto silicon to create more powerful chips. Many are already looking at extreme-ultraviolet lithography (EUVL) as a way to extend the life of silicon at least until the end of the decade. EUVL uses mirrors instead of lenses to focus the light, which allows light with shorter wavelengths to accurately focus on the silicon wafer. To learn more about EUVL, see How EUV Chipmaking Works.
DNA and Quantum
Beyond EUVL, researchers have been looking at alternatives to the traditional microprocessor design. Two of the more interesting emerging technologies are DNA computers and quantum computers.
DNA computers have the potential to take computing to new levels, picking up where Moore's Law leaves off. There are several advantages to using DNA instead of silicon:

• As long as there are cellular organisms, there will be a supply of DNA.
• The large supply of DNA makes it a cheap resource.
• Unlike traditional microprocessors, which are made using toxic materials, DNA biochips can be made cleanly.
• DNA computers are many times smaller than today's computers.

DNA's key advantage is that it will make computers smaller, while at the same time increasing storage capacity, than any computer that has come before. One pound of DNA has the capacity to store more information than all the electronic computers ever built. The computing power of a teardrop-sized DNA computer, using the DNA logic gates, will be more powerful than the world's most powerful supercomputer. More than 10-trillion DNA molecules can fit into an area no larger than 1 cubic centimeter (.06 inch³). With this small amount of DNA, a computer would be able to hold 10 terabytes (TB) of data and perform 10-trillion calculations at a time. By adding more DNA, more calculations could be performed.
Unlike conventional computers, DNA computers could perform calculations simultaneously. Conventional computers operate linearly, taking on tasks one at a time. It is parallel computing that will allow DNA to solve complex mathematical problems in hours -- problems that might take electrical computers hundreds of years to complete. You can learn more about DNA computing in How DNA Computers Will Work.
Today's computers work by manipulating bits that exist in one of two states: 0 or 1. Quantum computers aren't limited to two states; they encode information as quantum bits, or qubits. A qubit can be a 1 or a 0, or it can exist in a superposition that is simultaneously 1 and 0 or somewhere in between. Qubits represent atoms that are working together to serve as computer memory and a microprocessor. Because a quantum computer can contain these multiple states simultaneously, it has the potential to be millions of times more powerful than today's most powerful supercomputers. A 30-qubit quantum computer would equal the processing power of a conventional computer capable of running at 10 teraops, or trillions of operations per second. Today's fastest supercomputers have achieved speeds of about 2 teraops. You can learn more about the potential of quantum computers in How Quantum Computers Will Work.

Already we are seeing powerful computers in non-desktop roles. Laptop computers and personal digital assistants (PDAs) have taken computing out of the office. Wearable computers built into our clothing and jewelry will be with us everywhere we go.

Photo courtesy IBM By the end of the decade, we could be wearing our computers instead of sitting in front of them.

Our files will follow us while our computer provides constant feedback about our environment. Voice- and handwriting-recognition software will allow us to interface with our computers without using a mouse or keyboard. Magnetic RAM and other innovations will soon provide our PC with the same instant-on accessibility that our TV and radio have.

As the computer moves off the desktop and becomes our constant companion, augmented-reality displays will overlay computer-generated graphics to the real world.

One thing is an absolute certainty: The PC will evolve. It will get faster. It will have more capacity. And it will continue to be an integral part of our lives.

Have you ever thought about building your own computer? Actually buying a motherboard and a case along with all the supporting components and assembling the whole thing yourself? Here are three reasons why you might want to consider taking the plunge:

1. You will be able to create a custom machine that exactly matches your needs.
2. It will be much easier to upgrade your machine in the future because you will understand it completely.
3. You may be able to save some money.

And, if you have never done it before, you will definitely learn a lot about computers. ­ In this article, we'll take you through the entire process of building a computer. You'll learn how to choose the parts you will use, how to buy them and how to put them all together. When you're done, you will have exactly the machine that you need. Let's get started.
Decisions, Decisions

Determining what type of machine you want to build is the first step in building a computer. See more pictures of computer building.

Where do we start? Actually putting the machine together is pretty easy, but picking the parts and buying them takes research. The first step in building a computer is deciding what type of machine you want to build. Do you want a really inexpensive computer for the kids to use? A small, quiet machine to use as a media computer in the living room? A high-end gaming computer? Or maybe you need a powerful machine with a lot of disk space for video editing. The possibilities are endless, and the type of machine you want to build will control many of the decisions you make down the line. Therefore, it is important to know exactly what you want the machine to accomplish from the start.
Let's imagine that you want to build a powerful video editing computer. You want it to have a dual-core CPU, lots of RAM and a terabyte of disk space. You also want to have FireWire connectors on the motherboard. These requirements are going to cause you to look for a motherboard that supports:

• Dual-core CPUs (either Intel or AMD)
• At least 4GB of high-speed RAM
• Four (or more) SATA hard drives
• FireWire connections (possibly in both the front and back of the case)

Then it all needs to go in a case with enough space to hold multiple hard disks and enough air flow to keep everything cool. With any computer you build, knowing the type of machine you want to create can really help with decision-making.


Choosing a motherboard is the most interesting part of any building project. The reason it is so interesting is because there are hundreds of motherboards to choose from and each has its own advantages and disadvantages.
One easy way to think about motherboards is to break them up into a few categories. For example:

• Cheap motherboards: Generally in the $50 range, these are motherboards for older CPUs. They are great for building inexpensive machines.
• Middle-of-the-road motherboards: Ranging in price from $50 to $100, these are one step up from the cheap motherboards. In many cases you can find motherboard and CPU combos in this price range, which is another great way to build a cheap machine or an inexpensive home/office computer.
  
  
  
  

  A middle-of-the-road motherboard

• High-end motherboards: If you are building a powerful gaming machine or video workstation, these motherboards give you the speed you need. They range in price from $100 to $200. They handle the latest CPU chips at their highest speeds.
• Extreme motherboards: Falling into the over-$200 range, these motherboards have special features that boost the price. For example, they might have multiple CPU sockets, extra memory slots or special cooling features.

You need to decide whether you are building a "cheap machine," a "high-end machine" or a "tricked-out super machine" and then choose your motherboard accordingly. Here are some other decisions that help narrow down your motherboard choices:

Image courtesy Intel Corporation

• Do you want to use an Intel or an AMD processor? Making this choice will cut the number of motherboards in half. AMD chips are often cheaper, but lots of people are die-hard Intel fans.
• What size motherboard do you want to use? If you are trying to build a smaller computer, you may want to look at micro ATX cases. That means you will need to buy a micro ATX motherboard. Otherwise you can use a normal ATX motherboard and case. (There are also smaller motherboard form factors like mini-ITX and even nano-ITX if you want to go really small.)
• How many USB ports do you want? If you want several, make sure the motherboard can handle it.
• Do you need FireWire? It's nice if the motherboard handles it (although it is also possible to add a card).
• Do you want an AGP or PCI Express graphics card? Or do you want to use a graphics card on the motherboard to keep the price and size down? If you want to go the cheapest route, make sure the motherboard includes a video card on-board (easiest way to tell is to see if there is a DVI or VGA connector on the motherboard). PCI Express is the latest/greatest thing, but if you want to re-use an AGP card you already own, that might be a reason to go with AGP.
• Do you want to use PATA (aka IDE) or SATA hard disks? SATA is the latest thing, and the cables are much smaller.
• What pin configuration are you using for the CPU? If you want to use the latest CPUs, make sure that your motherboard will accept them.
• Do you want to try things like dual video cards or special high-speed RAM configurations? If so, make sure the motherboard supports it.

If you don't care about any of this stuff (or if it all sounds like gibberish to you), then you're probably interested in building a cheap machine. In that case, find an inexpensive motherboard/CPU combo kit and don't worry about all of these details.
Once you have chosen your motherboard, you are ready to choose everything else. Here's what you need to get:

• The CPU that's the right brand and the right pin configuration to fit your motherboard. Pick whichever CPU clock speed fits your budget and intentions. (If you purchase a motherboard/CPU combo, you can skip this step.)
• The RAM with the correct pin configuration that will match your motherboard. If your motherboard is using a specialty RAM configuration (normally to improve performance), make sure the RAM you buy matches its requirements.
• If the case does not come with a power supply, you'll need to choose one. Make sure its connectors match the motherboard. Three hundred watts are enough for most machines, but if you are building a gaming machine with multiple video cards or a machine with lots of disks, you may want to consider something bigger.
• Choose a video card if you are not using the onboard video on the motherboard. Make sure the card's connector is appropriate for the motherboard (AGP or PCI Express).
  
  
  
  

  A basic AGP-based graphics card

• Choose an optical drive. If you are building a cheap machine, get the cheapest CD-ROM drive you can find. If you want to burn DVDs and CDs, make sure the drive can handle it.
• Choose a hard disk, making sure that it matches the PATA/SATA status of your motherboard.
• Choose an operating system: Windows XP (which comes in home, professional and media center editions) or Linux in its hundreds of different forms.

­ Buying
Now that you have picked everything out, it is time to purchase your parts. You have three options:

• Mail order on the Internet - All kinds of stores sell computer parts on the Web. Visit a place like HowStuffWorks Shopper to compare prices. Don't forget about eBay.
• A big national chain - Places like Tiger Direct, Fry's, and CompUSA have stores in most large cities that will sell you parts. They also have people on staff who may be able to answer questions.
• local parts retailer - Any big city will have a number of smaller, local shops selling parts. Look in the Yellow Pages or online. I live in Raleigh, N.C., and a typical shop of this genre in Raleigh is called Intrex. The people working at a shop like this can often answer lots of questions, and they may also be willing to help you if your machine does not work after you assemble it.

Now that you have your parts, it is time to build. This is the fun part.
But before we start building, we need to say one thing about static electricity. Most of the parts you will be handling when you assemble your computer are highly sensitive to static shocks. What that means is that if you build up static electricity on your body and a shock passes from your body to something like a CPU chip, that CPU chip is dead. You will have to buy another one.
The way you eliminate static electricity is by grounding yourself. There are lots of ways to ground yourself, but probably the easiest is to wear a grounding bracelet on your wrist. Then you connect the bracelet to something grounded (like a copper pipe or the center screw on a wall outlet's face plate). By connecting yourself to ground, you eliminate the possibility of static shock.


Each combination of parts is unique. But in general, here are the basic steps you will need to follow when you assemble your machine.
Installing the Microprocessor and RAM
First, you'll need to unwrap the motherboard and the microprocessor chip. The chip will have one marked corner that aligns with another marked corner of its socket on the motherboard. Align the corners and drop the microprocessor into the socket. You don't need to apply any pressure - if it's aligned correctly, it should fall into place. Once you have it in, cinch it down with the lever arm.
Now, you need to install the heat sink. The CPU box will contain a manual that tells you how to do it. The heat sink will contain either a heat sink sticker or heat sink grease to use when mounting the heat sink on the CPU. Follow the instructions closely to install it. To install our heat sink, all we had to do was put it in place, cinch it down with flanges on either side and lock it with a cam. Connect the power lead for the heat sink to the motherboard.


Next, you'll install the RAM. Look on the motherboard for the slot marked "one" and firmly press the RAM module into it. It will probably take more pressure than you'd think to get the RAM into place. Each side of the module should also have a rotating arm that will lock the RAM down.
Now your motherboard is ready to put in the case.


Next, you'll assemble the case. You'll need to install the power supply, the motherboard, a faceplate and standoffs to hold the motherboard in place. You'll also need to connect some wires to the motherboard.


Your motherboard should have come with a face plate for its back connectors. The case already has a hole cut in it for the plate, so you just need to put in the plate and press it until it clicks into place. Now you can put in in the motherboard. It needs to sit about a quarter of an inch away from the case's surface so that none of its connectors touch the case. You'll accomplish this by placing spacers, which are also included with the motherboard.
Because each motherboard is different, you'll have to set it into the case first to see which screw holes on the motherboard match up with the pre-drilled holes in the case. Then you can take the motherboard back out, place the spacers, and put the motherboard in on top of them. Make sure that the motherboard lines up with the faceplate and the holes line up with the spacers.
Find the screws that fit (these should have come with the case) the spacers and screw down the motherboard. Don't screw them in too tightly -- they just need to be in snugly. Be very careful when putting in the screws. If you drop them into the case, they could damage the fine wires on the motherboard.

Installing the power supply.

Now you can install the power supply in the case if it's not already installed. The power supply has two sides. The fan side faces outside the case and the wire side faces inside. Slide the power supply onto its brackets and secure it with screws (the case or the power supply should have come with them).
Connect the power leads to the motherboard. There should be a large one and a small one, and it will be obvious as to where each one goes.
You'll be left with about 15 more wires. Don't worry -- the manual has a page to tell you exactly where each one goes. Each of them has a label that corresponds to a label on the correct port.
The last steps are installing the hard drive and the CD-ROM drive. The case has a removable bracket with four rubber grommets on it, which line up with four holes on the hard drive. It also came with four screws made just to punch through those grommets. Screw the hard drive into the bracket, then put the bracket back into its slot in the case. If you are using IDE/PATA drives, be sure to set the jumpers correctly. Then connect the hard disk to the power using one of the connectors coming off of the power supply. If it fits, then it's a match.


Now install the cables. One side of the cable has a red stripe on it, which makes it " pin 1." Look on the motherboard and hook the cable into the IDE connector marked "1." Insert the other end of the cable on the back of the drive. Now the drive is ready to go.
Install the CD-ROM drive next. Again, set the jumpers correctly. The drive fits in the front of the case, and you may have to pop out a faceplate to make room for it. Slide it in and screw it into place, making sure that it's aligned with the front of the case. Just as with the hard drive, you can use any available connector from the power supply. You'll also use the cable that came with the CD-ROM drive to connect it to the motherboard (align the red stripe for "pin 1") and plug the other end into the drive. Connect the audio for the CD drive. Again, there's an obvious place for it to plug in on the motherboard and on the drive itself.

Placing the hard drive into its bracket.

If you're using a video card, now you'll install it as well. Our motherboard has an AGP video slot so we have an AGP video card. The motherboard only has one video card slot, so you should be able to find it easily (you can also use the manual). Line up the card with the slot and push it into place. If the video card has its own power connector, connect it to the power supply. If the case has extra fans, make sure they have power too.
Now you can close up the case and add a monitor, keyboard, mouse and speakers. In the next section, we'll cover what to do after powering up the computer and what steps to follow if it doesn't work.
Now, the moment of truth -- it's time to turn your machine on and see if it works. If there's a switch on the back of the power supply, make sure it is on. Also make sure that the power supply is set correctly to 110 or 220 volts (some power supplies do this automatically, others have a switch or a slider).
Then push the power switch on the front of the case. In the ideal case, four things will happen:

• You will see/hear the fans spin up
• You will hear the hard disk spin up.
• Lights will light on the case.
• You will see something happening on the monitor to indicate that the motherboard is alive.

If you see/hear all of that happening, you are successful. You have created a working machine. Using the manual that came with the motherboard you can enter the BIOS screens and make sure everything looks OK. Chances are you will need to set the machine's date/time, but that is probably all you have to do. Everything else is probably automatic. All the drives will be recognized and auto-configured. The default settings on the motherboard will be fine.
The next step is to install the operating system. And presto, you have a working machine of your own creation. Congratulations!
Troubleshooting
What if you put it all together and it doesn't work? This is the one possible downside of building your own machine. It is hard to describe the feeling you get when you try turning on the machine and nothing happens. You have put in several hours of work and a significant amount of cash, so it's discouraging to get no response.
All is not lost, however. Here are several items to check:

• Is the power supply firmly plugged in and turned on (many power supplies have a small switch on the back)? Try a different outlet.
• Did you plug the power supply into the motherboard? Look at the manual for details.
  
  
  
  

  Make sure that your motherboard is connected to the power supply.

• Is the case's power switch properly connected to the motherboard? If you have plugged the switch into the wrong pins on the motherboard, it will not work. Check the motherboard manual.
• Are the drives connected to the motherboard properly? Do they have power?
• Unseat and reseat the video card. If the motherboard has onboard video, try to remove the video card completely and boot using the onboard version.

If you have checked all of that and nothing continues to happen, it could mean:

• The power supply is bad
• The switch on the case doesn't work. We actually had this happen once on a machine we built at HowStuffWorks.
• Something is wrong with the motherboard or the CPU.

The easiest way to determine where the problem lies is to swap parts. Try a different power supply. Swap a different motherboard into the case. Play around with different combinations. If it is still not working, then you have a few options at this point. You can go back to the shop that sold you the parts. If you bought them from a small local shop, they can help you debug the problem (although it may cost you). If they sold you a bad motherboard (rare, but possible) they will usually help you out. You can also try to find a more experienced builder who would be willing to help you. There is a rational cause for the problem you are experiencing -- either a bad part or a bad connection somewhere -- and you will find it.
Now that you've seen how simple it is to build your own computer, we hope that you'll give it a shot. You'll have a computer that you understand completely and will be easy to upgrade. You can save money, and it's a lot of fun too. So the next time you need a new computer, consider building it yourself!


Q: I am trying to build a computer and need some help with some terms that are being used.
1) What is an MGP Slot?
2) What connects to an ATX connector?
3) What connects to a FDD header?
4) What connects to a IDE header?
And, 5) do I need a 56K hookup?
A:
1) This is correctly a AGP graphics card as described above. It is faster then a PCI card, but if you are building your own ATX computer, it is most likely that the Graphic will be on the board. Unless you plan to be a gamer, don't waste your money on a AGP card, save it for a scanner.
2) ATX connector: ATX is a type of board. You have AT/ATX towers; you will want to make sure that the ATX board matches the ATX tower. As far as the connectors, ATX is a solid connection; an AT is a dual connection to the motherboard.
3) FDD connection is for your Floppy drive; this will be the smaller ribbon connector on the motherboard, and this ribbon then goes to the back of the Floppy drive.
4) IDE connection: There is a primary and secondary. Primary goes to your hard drive, secondary goes to your CD-ROM; these are the thicker ribbons. Make sure that the red line of the ribbon is inline with pin 1 on both of these; they also plug in the back.
5) 56K hookup: This is a PCI Modem that you will install into the white PCI Block for Internet; you should have software that comes with that card. Q:

As a computer technician, I have been told that I can build a new computer every six to eight months and deduct some or all of the machine built. I was told this by a teacher who claims to take this deduction every year. Is this deduction real/current and what are the terms to taking it?

A: You may only deduct the cost of the computer to the extent it is used for business purposes. Simply building a computer and letting it sit there does not make it deductible for tax purposes. If you sell the computer for a profit (i.e. sale price less your cost of materials) then you are taxed on the profit. Alternatively, if you build the computer and use it for business purposes, you may then deduct the cost (either through depreciating it or expensing it under Sec. 179) in proportion to its business use.

Because it is impossible for me to identify and consider ALL the relevant facts, this advice is not intended or written to be used for the purpose of avoiding penalties, and cannot be used for that purpose.
- Christopher Phelps -- Certified Public Accountant (CPA)


Q: I have an HP media center laptop. About a month ago it got very hot, turned off and since then I have not been able to get it back on. Here is what happens: When I plug the power cord into the computer, it sizzles and starts to smoke. Is it POSSIBLE that this is the power supply and that the entire computer is NOT destroyed?? Either way can anyone tell me what something like this would cost to repair??

A: While the whole computer itself may not be smoked, it does sound like at least the DC-DC converter board would need to be replaced. Where does the smoke actually come out from the computer? If it's right near the connection where the power supply plugs in, then it could be the DC-DC board. I would need the model number of the unit to determine a part cost for the board. If you're not comfortable opening the computer, it's probably between a $150-300 repair. Depending on the particular model and board, you might need to be friendly with a soldering iron also.
Joe -- Computer Systems Analyst

For most of the twentieth century, the only ways to watch television were through over-the-air broadcasts and cable signals. With broadcast TV, an antenna picks up radio waves to transmit pictures and sound to your television set. With cable TV, wires connect to a set-top box or to your TV itself. These wires run from your house to the nearest cable TV station, which acts as one big antenna. Aside from a few options like satellite TV, broadcast and cable were -- and still are -- the main ways to watch television.

© Photographer: Robert Mizerek | Agency: Dreamstime.com Internet TV could change the way we access information and entertainment.

New technology can change the way we receive news and entertainment, though. Radio challenged newspapers in the early 1900s, and television challenged radio. Now, it looks as though traditional television has its own competitor, but it's not one that's easily separated from television. It even has television in its name -- it's what we're now calling Internet TV.

Internet TV, in simple terms, is video and audio delivered over an Internet connection. It's also known as Internet protocol television, or IPTV. You can watch Internet TV on a computer screen, a television screen (through a set-top box) or a mobile device like a cell phone or an iPod.

Packets and Protocols An IPTV signal is basically a stream of data packets traveling across the Web. To learn more about the technical steps and protocols -- or rule sets -- involved, read this tutorial from the International Engineering Consortium.

It's almost the same as getting television through an antenna or a series of cable wires -- the difference is that information is sent over the Internet as data. At the same time, you can find even more variety on Internet TV than cable TV. Along with many of the same shows you find on the big networks, many Web sites offer independently produced programs targeted toward people with specific interests. If you wanted to watch a show on vegetarian cooking, for example, you could probably find it more easily over the Internet than on regular TV.
Because many sites offer on-demand services, you don't have to keep track of scheduling. For sites using webcasting or real-time streaming video, though, live broadcasting is still an option.

Internet TV is relatively new -- there are lots of different ways to get it, and quality, content and costs can vary greatly. Shows can be high-quality, professionally produced material, while others might remind you of Wayne and Garth broadcasting "Wayne's World" from their basement. Traditional TV networks are also easing into the technology and experimenting with different formats.


In this article, we'll go over the basics of Internet TV and talk about some of the current options for finding and watching it.

Mario Tama/Getty Images The Apple TV wirelessly connects computers to televisions and displays videos from iTunes.

Although video quality and screen size vary, right now Internet TV offers a few more benefits than traditional television does. It also offers a variety of options and formats. You can watch two basic types of broadcasts through Internet TV: live broadcasts or on-demand videos.
Web sites like wwiTV compile lists of live broadcast channels. If you want to catch up on the news in Buenos Aires, Argentina, for instance, simply click on Argentina -- channels are usually grouped by country -- and browse through the list of available broadcasts. Some TV networks also play live, streaming feeds of their programming on their official sites. Either way, it's like watching live TV on your computer screen. You can't pause, back up or skip through parts of the broadcast that don't interest you.
On-demand videos, on the other hand, are usually arranged like a playlist. Episodes or clips are arranged by title or channel or in categories like news, sports or music videos. You choose exactly what you want to watch, when you want to watch it. Comedy Central's official site, for example, features the Motherload, which lets you browse through prerecorded clips from programs such as "The Daily Show" and "The Colbert Report." Although it's not live television, you don't have to worry about networks taking down clips because of copyright issues.
In addition to the two basic broadcast categories, there are three basic fee structures for Internet TV:

• Free: Aside from the fee you pay for Internet connectivity, many Internet TV sites or channels don't cost anything. Many of these free sites are supported by advertising, so banner ads may show up around the site, or short commercials may play before you watch videos. It may seem a little bothersome to wait for video, but it's the only way for the Web site designers to make money and offer quality content for you to watch. Plus, the wait is never too long -- ad lengths can range from a few seconds to 30 seconds, which is still shorter than most commercials.
• Subscription: This works just like your cable bill. You typically pay a monthly fee for a certain number of channels or on-demand video. Prices are constantly changing since Internet TV is in its early stages, but subscriptions can cost as little as $20 and as much as $120, depending on the number of channels you want.
• Pay-per-view: Pay-per-view videos or podcasts can cost nothing if the site is free, and major networks generally charge between $3 and $7 for downloads and rentals.

The most popular ways to watch Internet TV are available in a variety of formats and costs. Joost, a free peer-to-peer program, offers shows from MTV, Comedy Central, CBS and Cartoon Network's "Adult Swim." Apple released the Apple TV in March 2007, and the device allows you to wirelessly transmit movies and TV shows from iTunes onto your television screen. Microsoft's Xbox Live Video Marketplace, on the other hand, lets Xbox 360 users download and rent movies and TV shows onto the system's hard drive.
To learn about how Internet TV is possible, read on to the next page.

Peer-to-peer Television Some Internet TV sites rely on peer-to-peer file sharing and require you to download a specific software client. Instead of receiving video from one central server, the software searches other computers with the same P2P program for a specific file. This is the same technology used for applications such as BitTorrent or the old Napster.

There are two things that make Internet TV possible. The first is bandwidth. To understand bandwidth, it's best to think of the Internet as a series of highways and information as cars. If there's only one car on the highway, that car will travel quickly and easily. If there are many cars, however, traffic can build up and slow things down. The Internet works the same way -- if only one person is downloading one file, the transfer should happen fairly quickly. If several people are trying to download the same file, though, the transfer can be much slower.
In this analogy, bandwidth is the number of lanes on the highway. If a Web site's bandwidth is too low, traffic will become congested. If the Web site increases its bandwidth, information will be able to travel back and forth without much of a hassle. Bandwidth is important for Internet TV, because sending large amounts of video and audio data over the Internet requires large bandwidths.

© Photographer: Zoltan Pataki | Agency: Dreamstime.com Think of bandwidth as a road. More lanes equals more room for traffic.

The second important part of Internet TV is streaming audio and video. Streaming technology makes it possible for us to watch live or on-demand video without downloading a copy directly to a computer.
There are a few basic steps to watching streaming audio and video:

1. A server holds video data.
2. When you want to watch a video, you click the right command, like "Play" or "Watch." This sends a message to the server, telling it that you want to watch a certain video.
3. The server responds by sending you the necessary data. It uses streaming media protocols to make sure the data arrives in good condition and with all the pieces in the right order.
4. A plugin or player on your computer -- Windows Media Player and RealPlayer are two popular examples -- decodes and plays the video signal.

Although Internet TV promises quite a lot, the concept doesn't come without criticism. Users with slow Internet connections may have difficulty getting data fast enough. Many complain that the video quality pales in comparison to HDTV screens, and Web sites have difficulty providing sufficient bandwidth. Peer-to-peer software may offer a possible solution, since it spreads out the amount of available information across lots of computers instead of putting all the pressure on one server.
Internet TV could eventually change the way we get our news and entertainment. People who are enthusiastic and knowledgeable about certain subjects but don't have a contract with a major network can produce their own shows if they have the right technology -- you can read more about what it takes in ­How Podcasting Works. Since video recording and editing technologies are becoming more accessible to the public, it will become easier to transmit user-generated content from all over the planet.

Whether you're using a desktop or laptop computer, there's a good chance that if you stop what you're doing and listen carefully, you'll hear the whirring of a small fan. If your computer has a high-end video card and lots of processing power, you might even hear more than one.
In most computers, fans do a pretty good job of keeping electronic components cool. But for people who want to use high-end hardware or coax their PCs into running faster, a fan might not have enough power for the job. If a computer generates too much heat, liquid cooling, also known as water cooling, can be a better solution. It might seem a little counterintuitive to put liquids near delicate electronic equipment, but cooling with water is far more efficient than cooling with air.

Image courtesy Darrin Gatewood A liquid-cooled PC in a clear case. See more liquid-cooled PC pictures.

A liquid-cooling system for a PC works a lot like the cooling system of a car. Both take advantage of a basic principle of thermodynamics - that heat moves from warmer objects to cooler objects. As the cooler object gets warmer, the warmer object gets cooler. You can experience this principle firsthand by putting your hand flat on a cool spot on your desk for several seconds. When you lift your hand, your palm will be a little cooler, and the spot where your hand was will be a little warmer.
Liquid cooling is a very common process. A car's cooling system circulates water, usually mixed with antifreeze, through the engine. Hot surfaces in the engine warm the water, cooling themselves off in the process.

Click on "Start" to see the fluid flow through the engine as the engine warms up.

The water circulates from the engine to the radiator, a system of fins and tubes with a lot of exterior surface area. Heat moves from the hot water to the radiator, causing the water to cool off. The cool water then heads back to the engine. At the same time, a fan moves air over the outside of the radiator. The radiator warms the air, cooling itself off at the same time. In this way, the engine's heat moves out of the cooling system and into the surrounding air. Without the radiator's surfaces making contact with the air and dispelling the heat, the system would just move the heat around instead of getting rid of it.
A car engine generates heat as a byproduct of burning fuel. Computer components, on the other hand, generate heat as a byproduct of moving electrons around. A computer's microchips are full of electrical transistors, which are basically electrical switches that are either on or off. As transistors change their states between on and off, electricity moves around in the microchip. The more transistors a chip contains and the faster they change states, the hotter the chip gets. Like a car engine, if the chip gets too hot, it will fail.
Most computers dispel this heat with heat sinks and fans. Heat sinks are basically pieces of metal that provide lots of surface area for the air to touch. The chip warms the heat sink, the heat sink warms the air, and the fan moves the warm air out of the PC case.

Image courtesy HowStuffWorks Shopper A heat sink uses lots of surface area to transfer heat from electronic components to the air.

This system works most of the time, but sometimes, electronic components produce more heat than simple air circulation can dispel. High-end chips with lots of transistors can overwhelm an air-cooling system. So can chips that have been overclocked, or manually set to work at faster than their default speed.

Cooling with a Terminator T-1000 In 2005, computing magazines reported that a liquid-metal cooled graphics card called the Radeon Blizzard X850XTPE would soon hit the market. Preliminary reports suggested that cooling with a liquid metal alloy was even more efficient than cooling with water. However, the card never made it to market, most likely because the cost of materials and production outweighed any improvement in cooling performance.

That's where water cooling comes in. Water has a higher thermal conductivity than air - it can move heat faster than air can. Water also has a higher specific heat capacity. It can absorb more heat before it starts to feel hot.
There are two reasons why a computer might need the increased thermal conductivity and heat capacity of water:

• Its electronic components produce more heat than the air around them can absorb
• The fans required to move enough air to cool all the components make too much noise or use too much electricity

In other words, there are two reasons why you might need to cool a computer with a liquid instead of air:

• The components inside your computer need more cooling than air alone can provide
• You want your system to be quieter

Next, we'll look at the components of a liquid-cooled system and how they work together.

All-in-one Units and Kits If you like the idea of liquid cooling but don't want to research individual components, you can buy a ready-to-use unit or kit. Self-contained units can plug directly into a computer's expansion slots or power supply and provide liquid cooling to one specific chip. Kits include all the parts you need and instructions for assembling them - just make sure the parts included are compatible with your computer's hardware. Some companies also sell high-end PCs with liquid cooling factory-installed.

A liquid-cooling system for a PC is a lot like a cooling system for a car. Coolant flows through channels in a car's engine block, and the rest of the cooling system incorporates:

• A pump that moves coolant through the system
• A radiator that dispels heat into the air
• A fan that moves air over the radiator
• A coolant reservoir that holds extra fluid and allows easy addition of coolant
• Hoses that connect the different parts of the system

Image courtesy Darrin Gatewood These water blocks can cool a GPU, a CPU and a northbridge.

Many electronic components do not tolerate direct contact with liquid. So instead of using channels to pump liquid directly through microchips as in a car engine, a liquid-cooled PC uses water blocks. A water block is a piece of heat-conductive metal, like copper or aluminum, that's filled with hollow tubes and channels. The bottom of the water block is a flat piece of metal that sits directly on top of the chip being cooled. Thermal paste between the chip and the block improves the heat transfer between the two surfaces. The chip heats the block, and the water absorbs the heat as it flows through all the channels.
Many central processing unit (CPU) water blocks are universal, but some graphics processing unit (GPU) water blocks only work with specific chips. You can also find water blocks designed to cool other high-temperature chipsets, like the northbridge, which connects your CPU to your memory. Usually, small bolts and washers attach the water block to the necessary printed circuit board (PCB), such as the motherboard or video card.
The rest of a liquid-cooling system's components are much like those found in a car's cooling system. Most liquid-cooled PCs have:

• A pump
• A radiator
• A fan
• A coolant reservoir
• Tubing

A centrifugal pump like the one used in your car

The pump is usually a centrifugal pump, much like you'd find in a car's cooling system. Some liquid-cooling pumps are submersible, and you can place them directly inside the coolant reservoir. Others need to be kept dry. If you're thinking about using a submersible pump, make sure its exterior doesn't get hot enough to heat all the fluid in the reservoir.
The pump is one of the most important parts of the system. Its flow rate determines how quickly the coolant moves through the tubes and blocks. If the water moves too quickly, it doesn't have time to absorb heat before moving on. If it moves too slowly, too much heat can build up around sensitive components. The complexity of the system affects the overall flow rate - the more resistance the fluid encounters within the blocks and radiator, the slower the overall flow rate.
The pump also has to be strong enough to move the liquid from the lowest point in the system to the highest. This is known as head pressure or vertical pressure, and it's especially important when liquid cooling tall server towers.

Image courtesy Amazon.com A pump for a liquid-cooled PC.

The system's radiator can be designed specifically for liquid-cooling systems, or it can be the heater core from a car. Heater cores dispel lots of heat - they provide the warm air for a car's heating system in the winter. However, they're not usually as attractive as radiators that are designed for use with a liquid-cooling system.
Not every liquid-cooled system has a fan, but most use one to help the radiator dispel heat faster. Similarly, not every system has a separate reservoir. Those that don't generally have a fill/bleed line for adding coolant and removing extra air from the system. Usually, the fill/bleed line leads to a filling port at the top of the computer's case.

Image courtesy Darrin Gatewood Many cooling reservoirs fit into a computer's drive bay.

In a liquid-cooled PC, the tubing presents a special challenge. It has to be flexible enough to connect components that may be at odd angles to one another. But it can't be prone to kinking - a kinked hose can severely restrict the flow of fluid through the system.
In a simple system, a tube connects the pump to the inlet of a water block. Separate tubes run from the water block's outlet to the radiator and the radiator to the reservoir, which often sits in one of the computer's CD-ROM bays. The final tube connects the reservoir back to the pump. For systems with multiple water blocks, tubes connect one block's outlet to the next block's inlet, connecting the blocks in series like a daisy chain.

Deep-fried PCs? Image © 2003 Ebo Eppenga Many electrical components can short-circuit when exposed to liquid, but some liquids can both dispel heat and act as electrical insulators. One such liquid is cooking oil. Check out what happens when you submerge a computer in oil at the Toms Hardware site or at Eppenga.com.

The final component of a liquid-cooling system is the liquid itself. Many people use distilled water, since tap water contains contaminants that can cloud the system or clog the channels in the water blocks and radiator. Specialized additives can add color to the fluid, making it more visually appealing when used in a clear case. They can also lower the freezing point or surface tension of the water, making it a more effective coolant. Finally, some additives have antimicrobial or anti-corrosion ingredients, which can increase the life of the system.

Image courtesy Darrin Gatewood In an operational system, tubes carry coolant to and from water blocks.

If you decide to install a liquid-cooling system in your computer, it's a good idea to let the pump circulate the fluid for a while so you can check for leaks. Keep your computer turned off during this test period so you'll be less likely to damage your hardware if a leak does occur.
Once you're sure that everything is watertight, boot up the computer. You can check the temperature of your components in your computer's BIOS menu or by using a third-party application that monitors temperature. If necessary, you can also apply smaller heat sinks to RAM chips and other higher-temperature components in your system.

Even as you read this article, computer chip manufacturers are furiously racing to make the next microprocessor that will topple speed records. Sooner or later, though, this competition is bound to hit a wall. Microprocessors made of silicon will eventually reach their limits of speed and miniaturization. Chip makers need a new material to produce faster computing speeds.
You won't believe where scientists have found the new material they need to build the next generation of microprocessors. Millions of natural supercomputers exist inside living organisms, including your body. DNA (deoxyribonucleic acid) molecules, the material our genes are made of, have the potential to perform calculations many times faster than the world's most powerful human-built computers. DNA might one day be integrated into a computer chip to create a so-called biochip that will push computers even faster. DNA molecules have already been harnessed to perform complex mathematical problems.
While still in their infancy, DNA computers will be capable of storing billions of times more data than your personal computer. In this article, you'll learn how scientists are using genetic material to create nano-computers that might take the place of silicon-based computers in the next decade.

Surpassing Silicon? Although DNA computers haven't overtaken silicon-based microprocessors, researchers have made some progress in using genetic code for computation. In 2003, Israeli scientists demonstrated a limited, but functioning, DNA computer. You can read more about it at National Geographic.

DNA computers can't be found at your local electronics store yet. The technology is still in development, and didn't even exist as a concept a decade ago. In 1994, Leonard Adleman introduced the idea of using DNA to solve complex mathematical problems. Adleman, a computer scientist at the University of Southern California, came to the conclusion that DNA had computational potential after reading the book "Molecular Biology of the Gene," written by James Watson, who co-discovered the structure of DNA in 1953. In fact, DNA is very similar to a computer hard drive in how it stores permanent information about your genes.
Adleman is often called the inventor of DNA computers. His article in a 1994 issue of the journal Science outlined how to use DNA to solve a well-known mathematical problem, called the directed Hamilton Path problem, also known as the "traveling salesman" problem. The goal of the problem is to find the shortest route between a number of cities, going through each city only once. As you add more cities to the problem, the problem becomes more difficult. Adleman chose to find the shortest route between seven cities.
You could probably draw this problem out on paper and come to a solution faster than Adleman did using his DNA test-tube computer. Here are the steps taken in the Adleman DNA computer experiment:

1. Strands of DNA represent the seven cities. In genes, genetic coding is represented by the letters A, T, C and G. Some sequence of these four letters represented each city and possible flight path.
2. These molecules are then mixed in a test tube, with some of these DNA strands sticking together. A chain of these strands represents a possible answer.
3. Within a few seconds, all of the possible combinations of DNA strands, which represent answers, are created in the test tube.
4. Adleman eliminates the wrong molecules through chemical reactions, which leaves behind only the flight paths that connect all seven cities.

The success of the Adleman DNA computer proves that DNA can be used to calculate complex mathematical problems. However, this early DNA computer is far from challenging silicon-based computers in terms of speed. The Adleman DNA computer created a group of possible answers very quickly, but it took days for Adleman to narrow down the possibilities. Another drawback of his DNA computer is that it requires human assistance. The goal of the DNA computing field is to create a device that can work independent of human involvement.
Three years after Adleman's experiment, researchers at the University of Rochester developed logic gates made of DNA. Logic gates are a vital part of how your computer carries out functions that you command it to do. These gates convert binary code moving through the computer into a series of signals that the computer uses to perform operations. Currently, logic gates interpret input signals from silicon transistors, and convert those signals into an output signal that allows the computer to perform complex functions.
The Rochester team's DNA logic gates are the first step toward creating a computer that has a structure similar to that of an electronic PC. Instead of using electrical signals to perform logical operations, these DNA logic gates rely on DNA code. They detect fragments of genetic material as input, splice together these fragments and form a single output. For instance, a genetic gate called the "And gate" links two DNA inputs by chemically binding them so they're locked in an end-to-end structure, similar to the way two Legos might be fastened by a third Lego between them. The researchers believe that these logic gates might be combined with DNA microchips to create a breakthrough in DNA computing.
DNA computer components -- logic gates and biochips -- will take years to develop into a practical, workable DNA computer. If such a computer is ever built, scientists say that it will be more compact, accurate and efficient than conventional computers. In the next section, we'll look at how DNA computers could surpass their silicon-based predecessors, and what tasks these computers would perform.


Silicon microprocessors have been the heart of the computing world for more than 40 years. In that time, manufacturers have crammed more and more electronic devices onto their microprocessors. In accordance with Moore's Law, the number of electronic devices put on a microprocessor has doubled every 18 months. Moore's Law is named after Intel founder Gordon Moore, who predicted in 1965 that microprocessors would double in complexity every two years. Many have predicted that Moore's Law will soon reach its end, because of the physical speed and miniaturization limitations of silicon microprocessors.
DNA computers have the potential to take computing to new levels, picking up where Moore's Law leaves off. There are several advantages to using DNA instead of silicon:

• As long as there are cellular organisms, there will always be a supply of DNA.
• The large supply of DNA makes it a cheap resource.
• Unlike the toxic materials used to make traditional microprocessors, DNA biochips can be made cleanly.
• DNA computers are many times smaller than today's computers.

DNA's key advantage is that it will make computers smaller than any computer that has come before them, while at the same time holding more data. One pound of DNA has the capacity to store more information than all the electronic computers ever built;­ and the computing power of a teardrop-sized DNA computer, using the DNA logic gates, will be more powerful than the world's most powerful supercomputer. More than 10 trillion DNA molecules can fit into an area no larger than 1 cubic centimeter (0.06 cubic inches). With this small amount of DNA, a computer would be able to hold 10 terabytes of data, and perform 10 trillion calculations at a time. By adding more DNA, more calculations could be performed.
Unlike conventional computers, DNA computers perform calculations parallel to other calculations. Conventional computers operate linearly, taking on tasks one at a time. It is parallel computing that allows DNA to solve complex mathematical problems in hours, whereas it might take electrical computers hundreds of years to complete them.
The first DNA computers are unlikely to feature word processing, e-mailing and solitaire programs. Instead, their powerful computing power will be used by national governments for cracking secret codes, or by airlines wanting to map more efficient routes. Studying DNA computers may also lead us to a better understanding of a more complex computer -- the human brain.