Java Reference
In-Depth Information
actually uses them, to memory, which operates at much faster speeds than permanent storage
devices can.
There are three main types of storage devices:
Magnetic disk drives
■
Optical disc drives (CD and DVD)
■
USB flash drives
■
Drives
are devices for operating a medium, such as disks and CDs. A storage medium
physically stores data and program instructions. The drive reads data from the medium and
writes data onto the medium.
Disks
A computer usually has at least one hard disk drive.
Hard disks
are used for permanently stor-
ing data and programs. Newer computers have hard disks that can store from 500 gigabytes to
1 terabytes of data. Hard disk drives are usually encased inside the computer, but removable
hard disks are also available.
CDs and DVDs
CD
stands for compact disc. There are two types of CD drives: CD-R and CD-RW. A
CD-R
is
for read-only permanent storage; the user cannot modify its contents once they are recorded.
A
CD-RW
can be used like a hard disk; that is, you can write data onto the disc, and then
overwrite that data with new data. A single CD can hold up to 700 MB. Most new PCs are
equipped with a CD-RW drive that can work with both CD-R and CD-RW discs.
DVD
stands for digital versatile disc or digital video disc. DVDs and CDs look alike, and
you can use either to store data. A DVD can hold more information than a CD; a standard
DVD's storage capacity is 4.7 GB. Like CDs, there are two types of DVDs: DVD-R (read-
only) and DVD-RW (rewritable).
USB Flash Drives
Universal serial bus (USB)
connectors allow the user to attach many kinds of peripheral
devices to the computer. You can use a USB to connect a printer, digital camera, mouse,
external hard disk drive, and other devices to the computer.
A USB
flash drive
is a device for storing and transporting data. A flash drive is small—
about the size of a pack of gum. It acts like a portable hard drive that can be plugged into your
computer's USB port. USB flash drives are currently available with up to 256 GB storage
capacity.
drive
hard disk
CD-R
CD-RW
DVD
1.2.5 Input and Output Devices
Input and output devices let the user communicate with the computer. The most common input
devices are
keyboards
and
mice.
The most common output devices are
monitors
and
printers.
The Keyboard
A keyboard is a device for entering input. Compact keyboards are available without a numeric
keypad.
Function keys
are located across the top of the keyboard and are prefaced with the letter
F.
Their functions depend on the software currently being used.
A
modifier key
is a special key (such as the
Shift
,
Alt
, and
Ctrl
keys) that modifies the nor-
mal action of another key when the two are pressed simultaneously.
The
numeric keypad
, located on the right side of most keyboards, is a separate set of keys
styled like a calculator to use for entering numbers quickly.
Arrow keys,
located between the main keypad and the numeric keypad, are used to move
the mouse pointer up, down, left, and right on the screen in many kinds of programs.
function key
modifier key
numeric keypad
arrow keys
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