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
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.
Click on the various parts of
the PC to learn more about how they
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 games.
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:
- The storing of frequently used data in extremely fast
RAM that connects directly to the CPU
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
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
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
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. 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
- 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 the computer.
disk - This is large-capacity permanent storage used to
hold information such as programs and documents.
system - This is the basic software that allows the user
to interface with the computer.
- Pronounced "scuzzy," the small computer system
interface is a method of adding additional devices, such
as hard drives or scanners,
to the computer.
Accelerated Graphics Port is a very high-speed
connection used by the graphics card to interface with the
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.
Connections 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
Monitor - The monitor
is the primary device for displaying information from the
Keyboard - The keyboard
is the primary device for entering information into the
Mouse - The mouse is
the primary device for navigating and interacting with the
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.
disk - The most common form of removable storage,
floppy disks are extremely inexpensive and easy to save
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.
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 (digital versatile disc, read-only memory) is
similar to CD-ROM but is capable of holding much more
Click on the various PC part
labels to learn more about how they
From Power-up to Shut-down 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
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
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.
This animation walks you
through a typical PC session.
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
Processor management - Breaking the tasks down into
manageable chunks and prioritizing them before sending to
Memory management - Coordinating the flow of data in
and out of RAM and determining when virtual memory is
Device management - Providing an interface between
each device connected to the computer, the CPU and
Storage management - Directing where data will be
stored permanently on hard drives and other forms of
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
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 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
You close the Web browser and choose the "Shut Down"
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
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.
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
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
As the computer moves off the desktop and
becomes our constant companion, augmented-reality
displays will overlay computer-generated graphics to the
Beyond EUVL, researchers have been looking at alternatives
to the traditional microprocessor design. Two of the more
interesting emerging technologies are DNA computers and
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
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.
Photo courtesy IBM By
the end of the decade, we could be wearing our computers
instead of sitting in front of
Already we are seeing powerful computers in non-desktop
computers and personal digital
assistants (PDAs) have taken computing out of the office.
Wearable computers built into our clothing
will be with us everywhere we go. 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.
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.
For more information, check out the links on the next page.