Chapter 2 Operating Systems 37
Operating systems allow application
software to communicate with the BIOS. The
BIOS translates the application software requests
into instructions the hardware can understand.
Examine Figure 2-1.
As you can see, users give instructions to the
computer system via application software such as
word-processing, graphics, and gaming. The user
can also give instructions directly to the operating
system. The operating system communicates with
the BIOS, which then communicates with the
computer hardware and peripherals.
Operating System
Characteristics
The way an operating system handles
activities, such as storing data, interfacing with
the user, and presenting information on the
screen, can be referred to as operating system
characteristics. Most operating systems appear
similar when judged by their screen display.
However, there are many differences in the way
they handle activities, especially data storage.
Multitasking
Multitasking is the ability of an operating
system to support two or more programs running
at the same time. When multitasking, it seems
to the user that both programs are running
simultaneously. However, in reality, they are not.
The computer simply switches control between
the programs, giving the illusion they are running
at the same time.
An example of multitasking is using the
printer while at the same time using e-mail,
surfing the Internet, or running another computer
application. The computer runs the software in
between sending packets of data to the printer.
Most operating systems support multitasking,
but the hardware may not. Systems designed
with minimal hardware, such as tablets and
smartphones, do not support multitasking very
well. If you attempt to perform more than one
task, the system will either not allow you to run
an additional program or the system will run
sluggishly because of the shared resources (CPU,
RAM, and chipset). The two major classifications
of multitasking are preemptive and cooperative.
Preemptive multitasking, sometimes
referred to as time slicing, is the process which
allows multiple programs to share control of
the operating system. For example, two or more
programs can share the CPU for processing
information. No single program can totally take
charge of the computer system. All programs
running in the preemptive mode of multitasking
share RAM. If two programs attempt to use
the same area of RAM at the same time, the
computer will lock up. Windows 95, Windows Me,
Windows XP, Windows Vista, Windows NT,
Windows 2000, OS/2, and MAC OS X use
preemptive multitasking.
Cooperative Multitasking
With cooperative multitasking, one program
dominates the operating system but will allow
another program to run while it is idle. This type
of multitasking is common to MAC OS 9 and
earlier and to Windows 3.x.
Figure 2-1. Typical relationship of computer hardware and
software components.
User User
Application Software
Operating System Software
BIOS
Computer Hardware
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