64 Computer Service and Repair
POST
As you can see in Figure 2-31, all operating
systems start out with a power-on self-test. The
power-on self-test (POST) is a simple diagnostic
program that is initiated when electrical power
is applied to the computer system. It is common
to all operating systems, even to MAC OS X and
all versions of Linux. The POST does a quick
system check to determine if all major hardware
components, such as the CPU, RAM, keyboard,
mouse, video system, and storage devices, are
in proper working order. The devices checked
may vary slightly from computer to computer
depending on the firmware.
The test it performs is not as sophisticated as
diagnostic software, but it will check for major
problems. When the POST is finished, it usually
makes one “beep” sound to let you know that the
POST is complete and everything is in working
order. If an error is detected during the POST, an
error code is usually displayed on the screen and
a series of beeps are heard that match the code.
The codes and beep pattern vary according to the
different BIOS or UEFI chip manufacturers. A list
of error codes and beep codes can be obtained
from the website of the manufacturer.
BIOS
In a BIOS-based system, the POST is initiated
by the bootstrap program in the firmware. The
bootstrap program is a short program that runs
the POST; searches for the Master Boot Record
operating system files. This section serves as an
introduction to the boot sequences of Windows XP,
Windows Vista, Windows 7, and Windows 8.
An in-depth understanding of boot sequences
is essential to troubleshooting startup problems.
Therefore, a more detailed description is presented
in Chapter 15—PC Troubleshooting.
The A+ Certification exams usually stress
knowledge of the boot sequence. Exercises
in the accompanying Laboratory Manual
will help you to better understand the boot
process.
A+ Note
Warm and Cold Booting
A computer cannot begin the boot sequence
if it is not initiated. When the boot sequence is
initiated, it is called booting the computer. There are
two styles of booting a computer: cold boot and
warm boot. A cold boot, also called a hard boot,
means that the electrical power switch is used
to turn on the computer. A warm boot, or soft
boot, is used to restart a computer that is already
running. A warm boot can be initiated by a
software program as part of a typical installation,
such as installing a game. Another common style
of initiating a warm boot is by pressing the [Ctrl],
[Alt], and
[Delete]
keys simultaneously or clicking
the
Restart
command located in the
Start
menu,
Figure 2-30.
Figure 2-30. A warm boot can be performed by clicking the
Restart command on the Start menu or pressing the [Ctrl],
[Alt], and [Delete] keys simultaneously.
Windows 2000 and XP Windows Vista, 7, and 8
POST POST
Initial startup phase Initial startup phase
Boot loader phase Windows Boot Manager
phase
Detect and conFig-
ure hardware phase
Windows Boot Loader
phase
Kernel loading phase Kernel loading phase
Logon phase Logon phase
Goodheart-Willcox Publisher
Figure 2-31. Comparison of Windows operating system boot
sequences.