When you enter CMOS Setup, usually pressing the DEL or F1 key right after the PC is powered up, you are presented with the Main Setup screen, a menu of major setup functions. The items with an arrow to the left will present their own submenu; the items without arrows fulfill a single function. One of the most important single function items is Load Fail-Safe Defaults. This option disables memory caching, high-speed drive access, and all performance enhancing features for troubleshooting. Load Optimized Defaults restores all these settings to where you really want them.
Main Setup screen
Standard CMOS Features, once the most frequented page in Setup, has lost most of its reason for existence to automatic drive detection. About the only occasion for which you might need to change settings here is if you are using a hard drive from an older system. If that's the case, before removing the drive from your old clunker, enter Setup there and write down the drive parameters and addressing mode (CHS, LBA, Large). When it's installed in your new system, select that hard drive on this screen and make sure the parameters match in the submenu (note the arrow to the left of the IDE items). If not, change from Auto to Manual and enter by hand.
Standard CMOS Setup
Although there are many user-configurable settings in Advances BIOS Features, most should be left at the default settings unless you are troubleshooting. (For example, you never want to use a PC with the Internet or external CPU cache turned off.) However, you can arrange the order in which the system will try boot devices here, particularly if you have trouble installing your operating system on a new system. It's also the place to change the boot-up status of the NUM LOCK key, which controls the numeric keypad on the far right of the keyboard and drives some of us nuts!
Advanced BIOS features
Advanced Chipset features defines how the motherboard chipset manages the onboard resources. Unless you are troubleshooting, you definitely want the system and video BIOS set "cacheable" so they can run at the speed of system RAM and not the Flash memory they are stored in. Also, if you are using Error Code Correction (ECC) memory DIMMs, you can tell the chipset how to handle error conditions; whether to stop dead and report or fix the error and continue.
Advanced Chipset features
Integrated Peripherals includes all the onboard peripheral controllers, such as the IDE controllers, USB ports, I / O ports and printer port. Generally, the default Auto selection is fine, but in troubleshooting, you may want to cut back the speed of the IDE bus (or temporarily disable DMA). You can even disable the IDE controllers entirely, replacing them with a PCI IDE controller. Note the vertical bar to the right of the menu area that indicates the whole screen isn't shown. You'll have to scroll down to get to the second serial port or the printer port.
Integrated Peripherals
Power Management encompasses not only power conservation settings but all power up and down functions. Here you can instruct the PC to come out of standby (a low power sleep mode) on modem, network, or other PCI adapter activity. You can also control how the power switch on the front panel functions, with a four-second delay or with immediate results. An important feature for servers is whether you want the PC to automatically power back up after a power outage shuts it down.
Power Management
PnP / PCI Configuration is another screen that you can leave alone if everything works, but which is invaluable for troubleshooting or getting older legacy adapters to work. You'll usually want to select PNP OS Installed (i.e., your are using a Plug and Play operating system such as Windows). If you can't get the operating system to recognize or allocate resources to an older adapter, you can allocate the resources manually here, IRQ and DMA, on a slot-by-slot basis. Also, if you try adding a new adapter to your PC and can never boot up afterward, you can try enabling Reset Configuration Data.
PnP/PCI Configuration
PC Health Status is the PC equivalent of the monitoring screens around a hospital bed in ICU, which hopefully you've only seen on TV. Not only is it helpful for troubleshooting overheating conditions and power supply problems, but it allows you to set a ceiling temperature at which the PC will shut itself down to prevent damage. The CD that ships with the motherboard usually contains a program that will display all this information from within your operating system.
PC Health Status
Frequency / Voltage Control is strictly for overclockers--techs who choose to exceed the manufacturer recommended settings for their CPUs and memory. The main dangers are overheating and instability, so the frequency control allows you to raise the basic clock speed in 1MHz increments while monitoring performance. Another side effect of overclocking can be shortened component life, though this isn't much of a concern to someone who wants the performance now. Frankly, I haven't fooled around with overclocking for more than 10 years because all the stuff seems awfully fast to me these days. 
Frequency/Voltage Control
None of the changes in CMOS Setup take effect unless you choose Save Exit, which you can reach directly from most Setup screens by pressing the F10 key. The two options on the Main Setup screen that we didn't mention are the Supervisor Password and User Password. The main reason most people might want to set a Supervisor Password is to prevent their kids from accidentally putting in a password and forgetting what it is, effectively cutting off access to the PC or Setup (password prompting is controlled by Security Options in Advanced BIOS Settings). The sole cure for a lost password is to open the PC and place the "discharge battery" or "forget password" jumper on the motherboard.
Save settings and exit
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