Specifications

CHAPTER 3
130
All About Motherboards
3. The OS configures the system and completes its own loading. The OS checks some
of the same settings and devices that startup BIOS checked, such as available
memory and whether that memory is reliable. Then the OS loads the core compo-
nents necessary to access the files and folders on the hard drive and to use memory,
the expansion buses on the motherboard, and the cards installed in these expansion
slots. The user is given a screen to log onto the system. The OS loads the software
to control installed devices, such as the mouse, the video card, the DVD drive, or
the scanner. These devices generally have device drivers stored on the hard drive.
The Windows desktop is then loaded using preferences assigned to the currently
logged in user.
4. Application software is loaded and executed. Sometimes an OS is configured to
automatically launch application software as part of the boot. After this, the user is
in control. When the user tells the OS to execute an application, the OS first must
find the application software on the hard drive, CD, or other secondary storage
device, copy the software into memory, and then turn control over to it. Finally, the
user can command the application software, which makes requests to the OS, which,
in turn, uses the system resources, system BIOS, and device drivers to interface with
and control the hardware.
USB
PCI
slots
Serial
port
Printer
port
Hard
drive
Floppy
drive
AGP
slot
Keyboard
Startup
BIOS
I have
these
resources.
I/O addresses 60–6F
and IRQ1, please!
System Resources
IRQ
0
1
2
.
.
.
15
DMA
channel
0
1
2
3
5
6
7
I/O
addresses
0
1
2
3
.
.
.
3FF
Memory
addresses
A0000
A0010
.
.
.
FFFFF
Figure 3-34 Boot Step 1: The BIOS startup program surveys hardware resources and needs and
assigns system resources to satisfy those needs
Courtesy: Course Technology/Cengage Learning
Notes
The four system resources on a motherboard that the OS and processor use to interact with
hardware are IRQ lines, I/O addresses, memory addresses, and DMA channels, all defined in Table 3-7.
Older systems using DOS and Windows 9x/Me required a technician to make decisions about managing
these resources when installing hardware devices, but newer systems generally manage these resources
without our involvement. For an explanation of how each resource works, see the content, “How an OS
uses system resources,” on the CD that accompanies this book.
A+
220-701
1.2
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