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What are those clunky characters on my monitor at bootup?

Updated on July 13, 2008
A typical BIOS screen for a zoomy Intel CPU.
A typical BIOS screen for a zoomy Intel CPU.

Every computer user has seen that antiquated 1960s type ASCII character screen that pops up as your PC starts up, but only a fairly small percentage of us have ever understood what all that stuff is, let alone delve into its mysterious functions. When your computer is first turned on, it literally doesn't know what it is. It could boot into a Windows environment or maybe a Linux one, or a Unix server or one of an almost infinite number of proprietary business or technical variants. The Basic Input Output System (BIOS) is how your computer knows how to start the process of launching into the Operating System you have chosen for it.

The BIOS is a tiny chunk of software that your PC utilizes to configure and test its various systems, including disk drives, memory, video, and all its various subsystems. The BIOS information is held in an Electrically Erasable Programmable Read Only Memory (EEPROM) that holds the current version of the program. Almost all BIOS chips on the market today are manufactured by either AMI or Phoenix. Even if your BIOS shows your PC manufacturer's name instead of AMI or Phoenix, it is most likely that you're running one of those same BIOSes but your manufacturer has licensed to use it under its own name.

The BIOS checks the information on the Complementary Metal Oxide Semiconductor (CMOS) which contain the PC's current settings. A tiny battery on the motherboard maintains electricity to the CMOS to ensure that data does not get erased even if the PC is unplugged for months or years. With the CMOS info, the BIOS now proceeds to configure the various computer subsystems to all work in harmony. Some of the functions that the BIOS controls is the order the disk drives will be polled for boot information, the loading of various interrupt handlers and device drivers to make the subsystems and attached peripherals work properly. After that's all taken care of, the BIOS turns its attention to the video subsystem and will either start its own onboard graphics controller or trigger a separate BIOS which resides inside a third party video card. Once video output is determined to be available, the BIOS runs the Power On Self Test (POST) where it confirms that the power supply voltages, checksums, onboard memory, input/output and video controllers are operating according to specification. This is why you'll often hear distraught computer enthusiast crying "My PC won't POST!"

Once the POST routine is completed and the graphics controller is enabled to show the amount of onboard RAM memory on the monitor, everything is A-OK and the boot sequence of the loaded Operating System can begin. That's when you start getting the Windows logos and in many cases go out for lunch, take in a movie, go for a stroll in the park and come back to wait for your Windows to load. If there is anyone to blame for that it's Bill Gates, it is most certainly not the fault of your BIOS which will usually perform all its duties in a matter of a few seconds!


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