A+ Essentials by vz9r6i


									A+ Essentials

Lesson 19


Learn about operating system, what they are, and what they do
Learn about the CPU operating modes
Learn how the operating system manages hardware

Mini Lesson

Operating modes

The CPU operates in 2 modes: 16-bit and 32-bit

16-bit is called Real mode. CPU processes 16 bits of data at one time. In Real mode an
application has complete access to all hardware resources. Programs written for Windows 3.1 are

32-bit is called Protected mode. CPU processes 32 bits of data at one time. In Protected mode,
the OS controls how an application can access hardware. In protected mode more than one
program can run at the same time. This is called Multitasking. In protected mode OS gives
programs limited and controlled access to hardware. Each program is protected from the other.
Programs written for Windows 95 and later are 32-bit.

How OS manages hardware

An operating system is responsible for communicating with hardware, but the OS does not relate
directly to the hardware. The OS uses device drivers or BIOS to interface with hardware. (Trend
is to manage devices with device drivers rather than BIOS)
Software can be placed into 3 categories:

Device drives or the BIOS
Operating system
Application software

Device drivers are small programs stored on the hard drive that tell the computer how to
communicate with a specific hardware device such as a printer or network card. These drivers
are installed on the hard drive when the device is first installed. Some of the device drivers are
part of the OS and the others come with the hardware devices when you purchase them.
Windows 2000/ XP has a Hardware Compatibility List (HCL) that determine if a driver will
work under Windows 2000/ XP. This list is on Microsoft web site. Sometimes manufacturers
will update the device drivers for improved performance. It is always best to work with the latest
driver for the hardware device.

BIOS is hard-coded or permanently coded into a computer chip called ROM BIOS chip. There
are 3 types of BIOS programs.

System BIOS – these are programs that control the Input/ Output devices
Startup BIOS – these are programs that control the startup of the computer
CMOS BIOS – these are programs to control the setup information stored in the CMOS. This is
accessed during startup. You will see a message to hold down Del key or F12 to change the
CMOS setup.


What are the two operating modes of the CPU?
What is the difference between the Real and Protected mode?
How does an operating system manage hardware?
What are device drivers?
What are the 3 types of BIOS?

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