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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 do.)
The illustration below shows themost 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.
Desktop computer system
Let's take a look at each of these parts.
System unit
The system unit is the core of a computer system. Usually it's a rectangular box placed on orunderneath 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 israndom access memory (RAM), which temporarily stores information that the CPU uses while the computer is on. The information stored in RAM iserased 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 ordevice.
System unit
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Storage
Your computer has one or more disk drives—devices that storeinformation on a metal or plastic disk. The disk preserves the information even when your computer is turned off.
Hard disk drive
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 almostall of your programs and files. The hard disk drive is normally located inside the system unit.
Hard disk drive
CD and DVD drives
Nearly all 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.
CD
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.

Tip
If you have a recordable CD or DVD drive, periodically back up (copy) your important files to CDsor DVDs. That way, if your hard disk ever fails, you won't lose your data.
Floppy disk drive
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 theyused to be, although some computers still include them.
Floppy disk
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.
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Mouse
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 doeslook 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.
Mouse
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...