1. POST and The Boot Process
Computer Technician
POST
and
The Boot Process
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2. 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
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3. 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
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4. Boot Step 1: POST Power-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 notice 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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5. Boot Step 1: POST Power-On-Self-Test
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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6. Boot Step 1: POST Power-On-Self-Test
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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7. Boot Step 1: POST Power-On-Self-Test
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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8. Bios Screen example
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9. Bios Screen example
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10. Plug and Play (PnP) Standard
Standard designed to make installation of hardware devices easier
Applies to OS, system BIOS, and hardware devices
ESCD (extended system configuration data) Plug and Play BIOS
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11. Boot Step 2: Loading the OS
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12. 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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13. Boot Step 2: Loading the OS
(DOS, 9x)
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14. Boot Step 2: Loading the OS
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15. Boot Step 3: OS Initializes Itself
Operating system completes the boot process, DOS core is loaded.
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16. Load the Shell/GUI DOS Prompt
Boot Step 4:
Load the Shell/GUI DOS Prompt
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