computer technician

Computer Technician

POST

and

The Boot Process

©UNT in Partnership with TEA 1

Booting Up Your Computer

Refers to the computer bringing itself up to an operable state without user intervention

Soft (warm) boot Uses OS to reboot

Hard (cold) boot Uses on/off switch More stressful on the machine

©UNT in Partnership with TEA Computer Technician - Boot Process 2

Overview of Boot Process

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


Boot Step 1: POSTPower-On-Self-Test

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.



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.


Boot Step 1: POSTPower-On-Self-Test1. 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.

2. CPU must exit the reset status mode and thereafter be able to execute instructions.

3. BIOS checksum must be valid, meaning that it must be readable.

4. CMOS checksum must be valid, meaning that it must be readable.

5. CPU must be able to read all forms of memory such as the memory controller, memory bus, and memory module.



6. 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.

7. I/O bus must be able to write / read from the video subsystem and be able to read all video RAM.

8. 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.


AMI Bios Screen


Phoenix Bios Screen


Plug and Play (PnP) Standard

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



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.



(DOS, 9x)

Boot Step 3: OS Initializes Itself


Operating system completes the boot process, MS-DOS core is loaded.

Windows 9x


Boot Step 4: Load the Shell/GUIDOS Prompt

computer technician

Documents

post boot errors

actual boot

step of post

post power

post errors

system memory

memory test

memory bus