If you use a
desktop computer, you might already know that there isn't any single part
called the "computer." A computer is really a system of many parts working
together. The physical parts, which you can see and touch, are collectively
called hardware. (Software, on the other
hand, refers to the instructions, or programs, that tell the hardware what to
The illustration below shows the most common hardware in a
desktop computer system. Your system may look a little different, but it
probably has most of these parts. A laptop computer has similar parts but
combines them into a single notebook-sized package.
Let's take a look at each
of these parts.
The system unit is the core of a computer system.
Usually it's a rectangular box placed on or underneath your desk. Inside this
box are many electronic components that process information. The most important
of these components is the central processing unit (CPU), or
microprocessor, which acts as the "brain" of your computer.
Another component is random access memory (RAM), which
temporarily stores information that the CPU uses while the computer is on. The
information stored in RAM is erased when the computer is turned off.
Almost every other part of your computer connects to the system unit
using cables. The cables plug into specific ports
(openings), typically on the back of the system unit. Hardware that is not part
of the system unit is sometimes called a peripheral device
Your computer has one or more disk drives—devices that
store information on a metal or plastic disk. The disk preserves the
information even when your computer is turned off.
Your computer's hard disk
drive stores information on a hard disk, a rigid
platter or stack of platters with a magnetic surface. Because hard disks can
hold massive amounts of information, they usually serve as your computer's
primary means of storage, holding almost all of your programs and files. The
hard disk drive is normally located inside the system unit.
computers today come equipped with a CD or DVD drive, usually located on the
front of the system unit. CD drives use lasers to read (retrieve) data from a
CD, and many CD drives can also write (record) data onto CDs. If you have a
recordable disk drive, you can store copies of your files on blank CDs. You can
also use a CD drive to play music CDs on your computer.
DVD drives can do everything that CD
drives can, plus read DVDs. If you have a DVD drive, you can watch movies on
your computer. Many DVD drives can record data onto blank DVDs.
If you have a
recordable CD or DVD drive, periodically back up (copy) your important files to
CDs or DVDs. That way, if your hard disk ever fails, you won't lose your
Floppy disk drives store information on floppy
disks, also called floppies or
diskettes. Compared to CDs and DVDs, floppy disks can store
only a small amount of data. They also retrieve information more slowly and are
more prone to damage. For these reasons, floppy disk drives are less popular
than they used to be, although some computers still include them.
Why are floppy disks "floppy"? Even
though the outside is made of hard plastic, that's just the sleeve. The disk
inside is made of a thin, flexible vinyl material.
A mouse is a small
device used to point to and select items on your computer screen. Although mice
come in many shapes, the typical mouse does look a bit like an actual mouse.
It's small, oblong, and connected to the system unit by a long wire that
resembles a tail. Some newer mice are wireless.
A mouse usually has two
buttons: a primary button (usually the left button) and a secondary button.
Many mice also have a wheel between the two buttons, which allows you to scroll
smoothly through screens of information.
When you move the mouse with your hand, a pointer
on your screen moves in the same direction. (The pointer's appearance might
change depending on where it's positioned on your screen.) When you want to
select an item, you point to the item and then click (press
and release) the primary button. Pointing and clicking with your mouse is the
main way to interact with your computer. For more information, see
A keyboard is used mainly
for typing text into your computer. Like the keyboard on a typewriter, it has
keys for letters and numbers, but it also has special keys:
The function keys,
found on the top row, perform different functions depending on where they are
keypad, located on the right side of most keyboards, allows you to
enter numbers quickly.
navigation keys, such as the arrow keys, allow you to move
your position within a document or webpage.
You can also use your keyboard to
perform many of the same tasks you can perform with a mouse. For more
information, see Using
displays information in visual form, using text and graphics. The portion of
the monitor that displays the information is called the
screen. Like a television screen, a computer screen can show
still or moving pictures.
There are two basic types of monitors:
CRT (cathode ray tube) monitors and LCD
(liquid crystal display) monitors. Both types produce sharp images, but LCD
monitors have the advantage of being much thinner and lighter. CRT monitors,
however, are generally more affordable.
A printer transfers data from a computer
onto paper. You don't need a printer to use your computer, but having one
allows you to print e‑mail, cards, invitations, announcements, and other
materials. Many people also like being able to print their own photos at
The two main types of printers are inkjet
printers and laser printers. Inkjet printers are
the most popular printers for the home. They can print in black and white or in
full color and can produce high-quality photographs when used with special
paper. Laser printers are faster and generally better able to handle heavy
Speakers are used to play sound. They
may be built into the system unit or connected with cables. Speakers allow you
to listen to music and hear sound effects from your computer.
To connect your computer to the Internet, you need a
modem. A modem is a device that sends and receives computer
information over a telephone line or high-speed cable. Modems are sometimes
built into the system unit, but higher-speed modems are usually separate