Transcript A+ Guide to Managing and Maintaining Your PC, 4e

Computer Technician
POST
and
The Boot Process
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Booting Up Your Computer
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Refers to the computer bringing itself up to an
operable state without user intervention
Soft (warm) boot
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Uses OS to reboot
Hard (cold) boot
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Uses on/off switch
More stressful on the machine
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Overview of Boot Process
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Step 1: POST (Power-on self test)
Step 2: ROM BIOS startup program searches
for and initializes an OS
Step 3: OS configures the system and
completes its own loading
Step 4: Load the Shell/GUI
Startup BIOS is in control for first step of the
boot, then it turns over control to the OS
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Computer Technician - Boot Process
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Boot Step 1: POST
Power-On-Self-Test
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The first thing that the BIOS does when it boots the PC is to
perform what is called the Power-On Self-Test, or POST for
short. The POST is a built-in diagnostic program that checks
your hardware to ensure that everything is present and
functioning properly, before the BIOS begins the actual boot.
It later continues with additional tests (such as the memory
test that you see printed on the screen) as the boot process is
proceeding.
The POST runs very quickly, and you will normally not even
noticed that it is happening--unless it finds a problem. You
may have encountered a PC that, when turned on, made
beeping sounds and then stopped without booting up. That is
the POST telling you something is wrong with the machine.
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Boot Step 1: POST
Power-On-Self-Test
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The speaker is used because this test happens so early
on, that the video isn't even activated yet! These beep
patterns can be used to diagnose many hardware
problems with your PC. The exact patterns depend on
the maker of the BIOS; the most common are Award and
AMI.
Some POST errors are considered "fatal" while others
are not. A fatal error means that it will halt the boot
process immediately (an example would be if no system
memory at all is found). In fact, most POST boot errors
are fatal, since the POST is testing vital system
components.
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Boot Step 1: POST
Power-On-Self-Test
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The first step of POST is the testing of the Power
Supply to ensure that it is turned on and that it releases
its reset signal.
CPU must exit the reset status mode and thereafter be
able to execute instructions.
BIOS checksum must be valid, meaning that it must be
readable.
CMOS checksum must be valid, meaning that it must
be readable.
CPU must be able to read all forms of memory such as
the memory controller, memory bus, and memory
module.
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Boot Step 1: POST
Power-On-Self-Test
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The first 64KB of memory must be operational and
have the capability to be read and written to and from,
and capable of containing the POST code.
I/O bus must be able to write / read from the video
subsystem and be able to read all video RAM.
If the computer does not pass any of the above tests
your computer will receive an irregular POST. An
irregular POST is a beep code which is different from
the standard which can be either no beeps at all or a
combination of different beeps indicating what is
causing the computer not to past the POST.
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AMI Bios Screen
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Phoenix Bios Screen
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Plug and Play (PnP) Standard
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Standard designed to make installation of
hardware devices easier
Applies to OS, system BIOS, and hardware
devices
Supported by Windows 98SE, Me and
Windows 2000/XP but not by Windows NT
ESCD (extended system configuration data)
Plug and Play BIOS
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Boot Step 2: Loading the OS
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Boot Step 2: Loading the OS
A hard drive might contain more than one logical drive. The
partition table at the beginning of the drive contains
information about the location of each logical drive, indicates
which drive is the boot drive, and holds the Master Boot
Record that begins the boot process for the operation system.
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Boot Step 2: Loading the OS
(DOS, 9x)
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Boot Step 2: Loading the OS
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Boot Step 3: OS Initializes Itself
Windows 9x
Operating system completes the boot process, MS-DOS
core is loaded.
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Boot Step 4: Load the Shell/GUI
DOS Prompt
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