Accessing your computer's CMOS Setup program is easy; you just press a key (or key combination) when the PC starts up. Different BIOS makers use different keys -- usually <Delete> or <F1>. Your monitor screen should announce which key(s) to press. If it doesn't, check your PC's documentation.

Once you reach the CMOS Setup program, you need to figure out how to get safely out of it. The main screen will list a number of submenus -- like Standard, Advanced, Security and Power Management -- as well as the program's exit options. Be sure to find the Exit Without Saving Changes option (or its equivalent). It's your escape route if you ever suspect that you've altered a setting that you didn't mean to change.

You may also notice one or two menu choices that allow you to restore CMOS settings to their default values. Before using one of these, check your documentation to determine which choice restores what. One option -- labelled something like "Restore BIOS Default" -- may return CMOS settings to a minimal configuration for troubleshooting purposes, an arrangement that sacrifices performance in favour of compatibility. Meanwhile, the other choice -- possibly labelled "Load Setup Default" -- may restore settings to the optimal performance-oriented values they were given at the factory.

Following are just a few of the CMOS settings that you may find useful. The precise names given below may not match the settings in your BIOS -- in fact, some may not even be offered in your setup program -- but you should be able to find their equivalents without much difficulty. As a rule of thumb, if you don't know what a setting does, don't play with it.

Hard Disk Settings: this table of settings, which in most cases is located under the Standard menu selection, holds the configuration parameters that your PC needs to recognise your hard disk. The hard disk settings table can record data for up to four drives, one for each of the four EIDE devices supported by most motherboards.

You can enter the hard disk parameters manually, but almost all PCs made in the last few years come with a hard-disk auto-detection program that reads and enters the proper configuration data into CMOS. If you like, you can run the program manually from the CMOS Setup program.

Floppy Disk: this option lets you select the type of floppy drive (for instance, one designed for 3.5in, 1.44MB floppies) that you have in your A: and B: drives. Check this setting if you find yourself running into floppy drive problems. Some BIOS versions have a separate Floppy Read Only setting that prevents data from being written to a floppy disk.

Boot Sequence: this setting determines the order in which the PC examines the drives for boot-up instructions. For example, it may begin with A: and go to C:. Or it may go from C: to the Zip drive, or from C: to A:. If you want to boot your machine from a CD-ROM, Zip, or LS-120 drive, you'll likely have to change this setting.

Password Protection: you can set the BIOS to ask for a password before you boot up, but be careful with this one. If you forget the password, you may have to reset a motherboard jumper, disconnect your CMOS battery (and lose all your settings), or even buy a new motherboard. (In some cases, your system manufacturer may be able to provide you with a "back door" password to use in an emergency -- if you can prove that you're the owner.)

Serial Port Settings: these are great places to investigate if you're having trouble installing a modem. Fixed IRQ and COM settings can wreak havoc on Windows and plug-and-play installations. For their part, serial ports may be turned on or off; so a serial port that seems dead may just be set to "disabled" in CMOS.

Parallel Port Settings: the preceding serial port tips apply here, too. These settings also let you select which mode -- standard, bi-directional, ECP, or EPP -- the parallel port uses, and they determine the speed and transmission capabilities of the parallel-port connection. Most printers manufactured three or more years ago use the slower, standard mode. Many new, full-featured printers won't function without ECP connections. Printer problems can often be traced to a parallel port with the wrong mode setting.

Fan RPM and CPU Temperature: you can find the correct values for both of these critical parameters in the CMOS Setup program. Check the settings here periodically to ensure they are accurate.