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Table Of Contents  CertiGuide to A+ (Core Hardware)
 9  Chapter 0001:  Power Supplies - System Board

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When you first turn on the PC, the system memory is empty, and even what the PC is made of, is not known. The system goes through a system boot sequence. While this process may vary slightly, overall it goes like this:

The power supply converts the AC power to DC, and starts charging capacitors. When the power supply is fully charged that sends a Power Good signal to the system board.

The CPU manufacturer pre-programmed the processor to look for the start of the BIOS boot sequence. The location of the BIOS the CPU is looking for is specifically set right at the end of system memory.

This allows for changes to be made in the actual size of the BIOS. Note that this point is only a reference point, with the location being instructions to jump to an actual starting point of the particular BIOS.

The first thing BIOS does is queries the CMOS about what is supposed to be in the PC. Then the Power On Self Test (POST) begins. This is a built-in diagnostic routine to ensure all parts and pieces are ready and accounted for.

Suppose you just installed a new video card, and in your excitement you neglected to fully press into place (seat) the video card.

The POST sequence cannot find a video card that isn't there. Without a video card it would be difficult to display an error message on a video screen. With this in mind, the BIOS sends a code through the PC speaker. Note that the codes vary from one BIOS manufacturer to another.

Assuming you have realized the error, powered off the computer, properly seated the video card, and re-started, a BIOS startup screen is displayed.

This screen displays the BIOS manufacturer and version number, along with the date of creation, and the one or more keys that must be pressed to get into the BIOS setup program. The particular key or keys must be depressed at this time to get into the setup program.

If the setup program is not entered, the System Configuration Summary is displayed. This data includes the:

  • CPU type

  • Math coprocessor

  • Clock speed of the processor

  • Style and capacity of all detected floppy drives

  • Hard drives

  • CD-ROM

  • Base memory

  • Extended memory

  • Type of memory

  • Display type

  • Serial or communication ports

  • Parallel or LPT (printer) ports

From this point the PC begins to attempt to find a device that has an operating system. That could be a floppy or more commonly, a hard drive.

Once that device is found, the Operating System begins to load. If everything is in order, you are ready to being your work or play.

Cold/ Warm Boot

on or pressing Reset performs POST. This is a Cold Boot. CTRL-ALT-DEL does NOT do POST. This is a Warm Boot.

With your computer ready to assist you with your work or play, the question arises, is it up to the task at hand? Some of that answer depends on what capabilities your PC has. Curiously enough, that is the next topic.

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CertiGuide to A+ (Core Hardware) ( on
Version 1.0 - Version Date: December 6, 2004

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