Specifications

CHAPTER 3
132
All About Motherboards
hard drives—ports, and other hardware devices are tested and configured. The
hardware devices that POST finds are checked against the data stored in the CMOS
chip, jumpers, and/or DIP switches to determine if they agree. IRQ, I/O addresses,
and DMA assignments are made; the OS completes this process later. Some hardware
devices have BIOSs of their own that request resources from startup BIOS, which
attempts to assign these system resources as requested.
14. Some devices are set up to go into “sleep mode” to conserve electricity.
15. The DMA and interrupt controllers are checked.
16. BIOS setup is run if requested.
17. BIOS begins its search for an OS.
STEP 2: STARTUP BIOS FINDS AND LOADS THE OS
After POST and the first pass at assignment of resources are complete, the next step is to
load an OS. The startup BIOS looks to CMOS RAM to find out which device is set to be
the boot device. Most often the OS is loaded from drive C on the hard drive. The minimum
information required on the hard drive to load an OS is shown in the following list. You
can see some of these items labeled in Figure 3-35.
Even though a hard drive is a circular affair, it must begin somewhere. A drive is laid
out in a series of concentric circles called tracks. Each track is divided into segments
called sectors, and each sector can hold 512 bytes of data. On the outermost track,
one sector (512 bytes) is designated the “beginning” of the hard drive. This sector,
called the Master Boot Record (MBR), contains two items. The first item is the master
boot program, which is needed to locate the beginning of the OS on the drive.
(A record and a sector are both 512-byte segments of a hard drive.)
The second item in the MBR is a table, called the partition table, which contains a
map to the partitions on the hard drive. This table tells BIOS how many partitions
Drive C
D
r
i
v
e
D
MBR program
Partition table holds
information about
where each partition
is located
Identifies boot drive
Drive C begins here
with the OS boot record
Master Boot
Record
Very beginning of
the hard drive
Hard drive
Figure 3-35 For a successful boot, a hard drive must contain a healthy Master Boot Record (MBR) and a
healthy OS boot record
Courtesy: Course Technology/Cengage Learning
A+
220-701
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