Information Technology Reference
In-Depth Information
Figure 4.3
Command-Based and Graphical
User Interfaces
While a command-based user
interface provides only a prompt for
text commands, a GUI provides
icons, menus, and dialog boxes to
support many forms of input.
Figure 4.3 also shows a
graphical user interface (GUI)
, which uses pictures (called icons)
and menus displayed on screen to send commands to the computer system. Many people
find that GUIs are easier to use because they intuitively grasp the functions. Today, the most
widely used graphical user interface is Microsoft Windows. Alan Kay and others at Xerox
PARC (Palo Alto Research Center, located in California) were pioneers in investigating the
use of overlapping windows and icons as an interface. As the name suggests, Windows is
based on the use of a window, or a portion of the display screen dedicated to a specific
application. The screen can display several windows at once. GUIs have contributed greatly
to the increased use of computers because users no longer need to know command-line syntax
to accomplish tasks.
graphical user interface (GUI)
An interface that uses icons and
menus displayed on screen to send
commands to the computer system.
Hardware Independence
To run, applications request services from the OS through a defined
application program
interface (API)
, as shown in Figure 4.4. Programmers can use APIs to create application
software without having to understand the inner workings of the OS.
application program interface
(API)
An interface that allows applications
to make use of the operating system.
Figure 4.4
Application
software
Application Program Interface
Links Application Software to
the Operating System
Application program
interface
Operating
system
Computer
system
hardware
Suppose that a computer manufacturer designs new hardware that can operate much
faster than before. If the same OS for which an application was developed can run on the
new hardware, the application will require minimal (or no) changes to enable it to run on
the new hardware. If APIs did not exist, the application developers might have to completely
rewrite the application to take advantage of the new, faster hardware.
