Mouse (I)
Optical Disk Drive (I/O)
A small hand-held device used by a computer
operator for positioning the cursor, making freehand
sketches, or selecting items from menus on a screen.
When the mouse is rolled across the surface of the desk,
the cursor moves a corresponding distance on the
screen.
Scanner (I)
A means of converting hand-drawn art or
photographs into digital form.
CD-ROM Drive (I)
CD-ROM (compact disk-read only memory)
technology is similar to audio disks, except it includes
routines for detection and correction of data errors. A
CD-ROM drive may be internally or externally
installed. It holds a vast amount of information that
makes it valuable to store digital images. Once
recorded, information on CD-ROM cannot be erased or
changed, but it can be read many times. The expression
Write Once, Read Many (WORM) describes this type
of technology.
Magnetic-Tape Unit (I/O)
The magnetic-tape unit moves magnetic tape across
read-write heads that actually read and write the
information. Data is recorded sequentially in the form
of magnetic spots along the entire length of the tape.
Magnetic-Disk Drive Unit (I/O)
The magnetic disk drive unit is a storage device that
reads and writes information on the magnetized
surfaces of rotating disks. The disks are made of thin
metal, coated on each side so data can be recorded in
the form of magnetized spots. As the disks spin around
like a music record, characters can be stored on them or
retrieved from them in a random (direct) manner.
Accessing data directly has several advantages over
accessing data stored sequentially. It provides fast
immediate access to specific data. You can direct the
disk drive to read at any point. Magnetic disk drives
come in two types: hard drives and floppy drives.
Magnetic disk drives are in computer systems and
electronic cameras. Floppy disks come in several sizes,
ranging from 3 to 8 inches in diameter; the 3 1/2-inch
diskette is most common.
A drive used with a form of data storage in which a
laser records data on a disk that can be read with a
lower-power laser pickup. Three types of optical disks
are used: Read Only (RO), Write Once, Read Many
(WORM), and erasable. Two types of erasable disks are
used: Thermo Magneto Optical (TMO) and Phase
Change (PC).
Printer (O)
The printer is a widely used output device that
expresses characters, graphics, drawings, or
photographs on hardcopy (paper or film). A large range
of printers is available. Printers are discussed in more
detail later in this chapter.
Monitor (O)
The monitor is similar to a television screen. It
allows you to see the program or data.
INPUT/OUTPUT CHANNELS
Input/output (I/O) channels provide a means of
communication between the CPU and peripheral
devices. This is accomplished by electrical cables that
carry both data and control information between the
computer and the peripheral devices.
Signals are transmitted and received through a
cable that connects the CPU to an on-line device. This
cable provides a path (channel) for the signal to travel.
Signals for both monitoring and data are transmitted by
way of I/O channels. These I/O channels may be used
specifically for data input, data output, or data input and
output. On desktop computers, the I/O channels are
referred to as communication ports.
Types of Channels
Channels, both input and output, may be either
simplex or duplex. A simplex channel is only capable
of communication in one direction. When a peripheral
device, such as a mouse, is connected to a simplex
circuit, it is only capable of transmitting data. Simplex
circuits are seldom used because a return path is
generally required for acknowledgment, control
information, or error message.
Duplex channels provide two paths for the
transmission of data. One path is for sending, and one
is for receiving data.
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