BIOS (Basic Input/Output System)

The place where you can make changes to the BIOS is known as the CMOS (pronounced "see-moss"). The term CMOS comes from the type of low-voltage Complimentary Metal-Oxide Semiconductor chips used for actually storing the changes you make.

Sometimes the CMOS is called by other names such as: the CMOS menu, the Setup, the Setup menu, the System Configuration, the System Configuration Menu, the System Configuration Utility, the Computer Setup Menu, or the Configuration Setup Utility.

More about the CMOS.

The CMOS is where you can tell your computer about a new hard disk drive or floppy disk drive you've added to your system. Most of the time you'll find your CMOS is divided into several pages of information, navigated by arrow keys although some CMOS menus allow you to use your PC's mouse to move around.

How to get into the CMOS.

If you want to take a look at your computer's CMOS, the most common way is to enter a special key squence during the time when your PC starts. If you watch your monitor when your PC starts, the BIOS sometimes will tell you what the key squence is.

The most common key squence is to type the Del key while the PC starts. Other common keystrokes are to press the F1 or F2 key. You may find pressing more than one key at a time is necessary, such as pressing Ctrl, Alt, and S keys at the same time.

Most PC manufacturers purchase their BIOS's from well-known vendors and them modify the BIOS within certain parameters to meet the requirements of the company's PCs. However, there are manufacturers who develop a proprietary BIOS specifically for the company's line of computers. Computer manufacturers IBM and Compaq work this way.

The proprietary BIOS

A proprietary BIOS often requires a particular set of keystrokes or a special software program in order to enter the CMOS menu. If you have your user documentation, you can look there. If not, you usually go to the web site of the vendor in question and look up the information by the model number of your computer.

For example, to enter the CMOS on some models of IBM Aptiva computers, you must press F1 when a small box known as the "POST Configuration Icon" appears on the monitor during the boot sequence. (POST stands for Power On Self-Test.) Many models of Compaq computers store the CMOS information on the computer's hard disk drive, so you need a special software program to access the CMOS and make changes. (This is especially important to note if you're adding a new hard disk drive to a Compaq computer.)

The CMOS and the battery backup

There's one more thing you should know about the CMOS. In order for the CMOS to maintain your changes when your computer is off, there's a small battery to maintain power. If this battery loses power, then your computer can forget all settings, including hard disk drive settings.

It's possible to upgrade your BIOS. This can be done either by a physical replacement of a chip on your motherboard or via software. The type of BIOS that's software upgradeable is known as a flash BIOS. A flash BIOS is stored in integrated circuit (IC) chips that can be rewritten via a software program.

Why do a BIOS upgrade?

I'm not trying to sell you on performing a BIOS upgrade. However, these upgrades are interesting and can be useful if you do your homework beforehand.

BIOS upgrades are most commonly performed to obtain fuctionality not present in the previous BIOS. For example, on PCs such as those with 386, 486, and some Pentium processors, the BIOS was unable to recognize any disk space over approximately 500 MB in hard disk drives larger than than that size. (The exact size barrier varies between 500 and 540 MB depending on the BIOS.) While memory-resident software is available to get past this barrier, a BIOS upgrade was common cure to get past the 500 MB road block to hard disk drive size.

Currently, BIOS upgrades are commonly performed to allow for support of new components for the PC. One example, a BIOS upgrade might be performed so the computer can support the new LS-120 floppy disk drives. The LS-120 looks like a standard 3.5-inch floppy disk drive and is capable of reading 720K and 1.44MB diskettes. However, it's designed to allow the storage of about 120 MB of data on a specially designed 3.5-inch size diskettes.

How do I get a BIOS upgrade?

In order to upgrade your BIOS, you must know the date and manufacturer of the BIOS you have now. That's done by either watching the computer when it comes up and noting any version numbers as well as the manufacturer and date, or by entering the BIOS and noting the version numbers there.

It's important to know what version BIOS you have now so you can make sure an upgrade is available. To give you an idea of what you're looking for in determining the version of your current BIOS, let's look again at the examples from earlier.

In the system start up message for an Award BIOS displayed below, you can see the final date of the copyright is 1997. That's the date to pay attention to. Also the manufacturer is Award Software, Inc. and the version is the Modular BIOS v4.51 PG.

BIOS Manufacturers

Question: I've heard that I can goof up my system by viewing my CMOS. Is that true?

Answer: Most CMOS menus require you to deliberately choose to save the changes you make. You can view your CMOS settings risk-free if you are sure to choose the option of exiting without saving your changes.

Another thing to watch out for is some computers, especially laptops, will let you into the CMOS menu at anytime the PC is running instead of just during the start-up squence. While this can be convenient, it can also be a problem if the PC automatically restarts itself after you leave the CMOS. This will cause improper shut down of any applications running or of Windows. Improper shut down can cause lost clusters, file corruption, and other problems.

To avoid these problems, the best thing to do is to enter the CMOS menu from the DOS prompt with no other applications running, including Windows. For example, shut down Windows 95 or 98 with the Restart in MS-DOS mode option. Once at the MS-DOS prompt, type the keystrokes to enter the CMOS menu.

Question: If I add memory to my motherboard, how do I tell the BIOS the memory is there? Do I enter the memory in the CMOS menu?

Answer: You don't need to tell the BIOS about more memory -- it will automatically pick up the additional memory when your system starts. However, some CMOS menus require you go in and save the new amount of memory manually. This amounts to entering the CMOS and then saving the changes as you exit. You don't have to enter the new amount of RAM (and there's no way for you to enter the amount of RAM anyway) because the BIOS picked up that information from the motherboard when the system started. It just cannot save the new CMOS settings without your help.

You'll know if you need to save the new CMOS memory settings in your system because the BIOS will report a mismatch. It will then either automatically start the CMOS menu for you or ask if you want to enter the CMOS menu each time the computer starts. All you have to do to prevent this is save the changes to the CMOS when you exit. Then the system should boot normally.

Question: What if I password protect my CMOS, then forget the password. Can I get back into my CMOS?

Answer: Probably. As mentioned earlier, the CMOS is powered by your system's battery. If you can remove or otherwise disconnect the battery power, then over a period of a few days, your CMOS will forget everything, including the password. You just need

The rub here is two-fold. First, you need to have the type of battery you can remove or disable, and not all systems have batteries that are easily disabled. And second, your CMOS will forget everything, so it's a good idea to have written down the CMOS settings. But without either diagnostic software or a BIOS that displays it's settings during the boot, you won't be able to write down the settings because, of course, you can't get into the CMOS menu to see them.

If you have a removeable battery, be sure to note how the battery was connected so you can reconnect it correctly after the CMOS forgets everything. When you restart the system, you should see an error message from the BIOS that says something like CMOS checksum error or CMOS checksum bad. You should be able to enter the CMOS without a password at that point. Power down the system, reconnect the battery, re-enter the CMOS, and enter the settings you hopefully were able to write down. (For those of you who have a copy of Upgrade Your Own PC, photos and detailed information on battery replacement is found in Chapter 10.)

Question: Do some BIOS's have a limit to how much RAM you can add to your PC?

Answer: It's not really a limit as much as a bug. BIOS's developed for the Pentium 90 and 100 MHz processor motherboards and earlier BIOS's have trouble addressing more than 64MB of RAM. If you add more than 64MB of RAM, the BIOS will recognize the memory, but you'll start getting errors during the operation of the computer such as General Protection Faults (GPFs) in Windows. I'd recommend you avoid adding more than 64 MB of RAM to systems with BIOS's dated 1996 or earlier.