Boot Sequences, The BIOS, The CMOS, and the POST

Another one of the most critical parts of the computer you must understand is the BIOS.  BIOS Stands for Basic Input/Output System, and contains all the programming your motherboard needs in order to boot your computer.  

The BIOS is in charge of remembering what equipment you have inside your computer, and how to boot that hardware so the computer can run.  Essentially, the programming inside the BIOS is the first instructions your computer receives when it turns on.  It tells the video card to start, the hard drives to initialize, and your keyboard how to work.  Without the BIOS the computer couldn't initialize to run your operating system.

The BIOS is invoked by what's known as a jump instruction.  The jump instruction is located at address FFFF0h in conventional memory.  This happens to be the first location that the microprocessor is designed to look at and run.  This in turn runs the POST, and then performs the necessary instructions to start the operating system.

Most BIOS's you will come across today are referred to as EEPROM. (Electrically erasable, programmable, read only memory)  This allows the BIOS to be updated to allow for new versions of hardware to be recognized through a process called Flashing.  Flashing the BIOS is essentially re-writing the BIOS by sending a specific electrical charge through the BIOS chip.  

To be honest, there are not many instances where flashing a BIOS will actually cure a problem on a motherboard.  BIOS's are built pretty standard, and all the peripheral equipment inside a computer is generally built around the BIOS types.   If you are having a problem with a particular piece of equipment, it is possible that the BIOS may be responsible.  Check the web site of the vendor of the BIOS, the motherboard, and the peripheral for more information.  To find out what BIOS you are working with, watch the top of the screen after the video BIOS boots for the manufacturer and the version number of the BIOS.  

What is important to know is the boot sequence that is invoked by the BIOS.  Knowing the cold boot and warm boot processes of a system. A cold boot is a boot performed when the computer has been totally powered off and then powered on again.  A warm boot is a boot that occurs when Windows is told to restart, or you press Cntl-Alt-Del in order to re-set the system.  Below is the standard cold boot sequence for most computers.

A warm boot is essentially a cold boot that starts at #5.

Beeps, Blips, and POST codes

The POST has an ingenious system for telling you when something is critically wrong with your system.  If nothing is wrong with the system, a single beep is emitted through the system speaker and the boot sequence continues.  If errors do occur, a series of beeps will emit.  Unfortunately, some beeps on some BIOS's don't mean the same thing on other BIOS's.  There is a standard, but to be sure you have the right code check the BIOS manufacturer's web site.  Thankfully, newer BIOS's have been programmed to show non-video beep codes on-screen.  Here is the Award/Phoenix and AMI POST code lists;

Knowing what the beeps signify is not as important as knowing what an individual error message means.  Make sure you can identify the major system errors and what they mean.  There may also be a question on BIOS setup keys; Most BIOS's require you to press the Delete key or F10 to enter the BIOS setup.  Lastly, the BIOS screen will normally also show a logo called the Energy Star Compliance Logo.  Be aware that this means that the BIOS is compatible with Energy Star's guidelines for power usage and power-down modes.

CMOS

The Complimentary Metal-Oxide Semiconductor, or CMOS, was introduced in the 286 processor line as a means of storing BIOS information.  Before CMOS, all the hardware information on a computer was stored on Dip switches on the motherboard.  This system was cumbersome and made creating unique peripherals difficult for manufacturers.  By using a CMOS and a back-up battery, BIOS's became able to store system information without the use of dip switches.  If you want to see the CMOS battery, look for the quarter-sized round lithium cell on the motherboard.  Problems with BIOS's not keeping their information can normally be solved by replacing this battery.

Some older systems had lithium cells soldered to their board.  This made replacement more difficult, as the old battery had to be cut out and a new one soldered in place.  Because the CMOS runs at about 3 volts, some inventive technicians simply bypassed this battery and replaced it with another 3.6 volt cell or two AA batteries in a holder Velcro-ed to the side of the case.  Although this hasn't happened since the late 486 era, be aware that if you unplug this battery system from the main board you will erase the CMOS.

BIOS's also have the ability to be password protected.  This was done to keep unscrupulous users from entering the BIOS and messing with the settings inside.  (I had a friend that made a regular visit to the local computer store to reset their BIOS's and erase their operating systems...  He found some form of perverse pleasure from it.)  If you run across a BIOS that is password protected, you should try and find the password before proceeding.  If you can't find the password, there is a way to erase the CMOS's memory.  Most motherboards have a jumper close to the CMOS battery through either removing a jumper or shorting the pins out will erase the CMOS.  If you can, consult the motherboard manual.  If you can't, here's a few tricks I remember.  #1 Pins that must be shorted generally must be shorted for several minutes.  The data retention ability of the CMOS requires the jumpers to be shorted for up to 5 minutes.  #2 If you can't find the jumpers, remember that removing the CMOS battery will serve the same function.  Press down on one edge and insert a flat head screwdriver under the lip and pull it slowly out.  Again, wait about 5 minutes before returning the battery to it's holder.  #3 If you do remove the battery, remember that it will go in writing-side up, and be careful of the metal tap that stretches out across the battery.  If you break this piece of metal, you may not be able to make good contact with the negative connection on the bottom.

The BIOS Setup Utility

In order to put the information into the CMOS, you must use the BIOS setup utility.  Again, this is entered through a keystroke or series of keystrokes during the POST.  Most motherboard's use the Delete key, but F10, Alt-Esc, Ctrl-Esc, Ctrl-Alt-Esc, F1, and F2 have been known to be used.  Whichever format is used, a new screen (usually blue) will show up with several menu items.

In the modern BIOS utility there are an average of 120 settings that can be modified.  The wording on many of these may change, but the meanings remain the same.  Here is the list of the most important CMOS settings.

As well as the setting described in the CMOS, there are several other settings on a motherboard that are user-serviceable.  These control items such as CPU clock speed, CPU multiplier, and Memory timing.  Consult the motherboard manual for proper settings for these jumpers, as each motherboard has it's own settings for each jumper.

In Conclusion...

Most of the information on BIOSes and CMOSes that you will be tested is non-consequential by today's standards.  Besides some basic CMOS settings, the motherboard can control most of the options and provide the faster, most stable configuration automatically.  The reason this information is still on the test is the increasing number of older systems that do not have this ability that users continue to use.  Therefore, you will not use most of this lesson on a new computer, but may be forced to look back at it to fix a computer from ages past. 

I remember my first experience with an older computer.  I had a gentleman that wanted to put a 386 board to upgrade his existing 286 computer.  Unfortunately, he had an old MFM hard drive and controller that was 8086 era.  He had the MFM controller card hooked up to a standard I/O 286 board which then connected to an MFM hard drive. I was totally lost, and ended up having to call for back-up a couple of times to guide me through it.  No matter how outdated the equipment people use may seem, it's still their computer and you should have some idea how to work with it.