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 Web and play
In this edition of
HowStuffWorks, 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.
On the Inside
Let's take a look at the main components of a typical desktop computer.
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.
- 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:
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
input/output system (BIOS) - A type of ROM that is used by the
computer to establish basic communication when the computer is first
- 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
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
from a device (like a
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
stored on a device (like a
or sent somewhere else on the network (back through the modem or network
We have lots of special-purpose processors in our lives. An
MP3 Player is a
specialized computer for processing MP3 files. It can't do anything
else. A GPS is a
specialized computer for handling GPS signals. It can't do anything
else. A Gameboy
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.
supply - An electrical transformer regulates the electricity used by
- 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.
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
- 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.
card - This translates image data from the computer into a format that
can be displayed by the monitor.
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
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
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.
Parallel - This port is commonly used to connect a
- This port is typically used to connect an external
- Universal Serial
Bus (USB) - Quickly becoming the most popular external connection,
USB ports offer power and versatility and are incredibly easy to use.
(IEEE 1394) - FireWire is a very popular method of connecting
digital-video devices, such as
digital cameras, to your computer.
- Internet/network connection
From Power-up to
Now that you are familiar with the parts of a PC, let's see what happens in
a typical computer session, from the moment you turn the computer on until
you shut it down:
- You press the "On" button on the computer and the monitor.
- 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:
- Floppy and hard drive
- BIOS revision and date
- 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.
- 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
- 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
- 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
- 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
- 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
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
- 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.
The Future of Computing
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
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
As the computer moves off the desktop and becomes our
constant companion, augmented-reality displays will overlay
computer-generated graphics to the real world.
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.
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
- 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
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
How DNA Computers Will Work.
Today's computers work by manipulating
bits that exist in
one of two states: 0 or 1.
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
Computers Will Work.
By the end of the decade, we could be wearing our
computers instead of sitting in front of them.
Already we are seeing powerful computers in non-desktop roles.
and personal digital
assistants (PDAs) have taken computing out of the office. Wearable
computers built into our
will be with us everywhere we go. Our
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.
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.