TCS - CMOS

CMOS

by Dick Maybach
Brookdale Computer Users Group
From the June 2003 issue of the I/O Port Newsletter

When you first turn on your PC, no programs are loaded into RAM; instead, a program, called the Basic Input Output System (BIOS), which is permanently stored in Read - Only Memory (ROM), begins the boot process. It consults a small non-volatile memory (meaning that it doesn't lose information when you shut off the power) which stores your PC's configuration. This memory is called CMOS, because it was originally implemented using Complementary Metal Oxide Semiconductors. It keeps such information as the configurations of your hard and floppy disks, from which disks to boot, the date and time, power management (what to shut down after an idle period), and configurations of any non-plug-and-play expansion cards. You must edit this if you add hard or floppy drives or if you add non-plug-and-play expansion cards. Because making an error here can disable the PC, many people are reluctant even to look at it. However, with a little care, you can safely explore CMOS and change the data to fit your needs.

To access the CMOS configuration program, watch the screen carefully as your PC boots. You will see a brief message on what keys to press to configure the computer. Common ones are F1, F2, F10, Esc, Ins, and Del. You may have to reboot more than once to catch the message. Once you know what to do, place your finger over the correct key or keys and reboot again and repeatedly (once a second or so) press the key(s) until you see the CMOS set-up screen.

Before you do anything, carefully read everything on the screen. Note especially the instructions, usually at the bottom. You will see there are two ways to exit the program, one saves any changes you've made and the other discards them. The second one is the key to safe exploring. You should always exit without saving changes, unless you are sure what you've done is correct. So long as you do this, there is little chance of creating problems.

There are three kinds of items on CMOS screens, parameters that you can edit, action buttons, and new pages that you can select. With some BIOS's, you change screens with a key press (ALT-P on my desktop for example), and these won't have items of the last type. Approach action buttons with care. Two common action buttons are "Load BIOS defaults" and "IDE auto-detect". The first sets all the parameters to values the motherboard manufacturer thinks are reasonable. They probably aren't all correct for your PC, and if you select this, you may have to reset some parameters. The second queries the hard disk and sets up the BIOS parameters to match. This is almost certainly safe, unless your hard disk was set up incorrectly.

Your first task should be to navigate all the CMOS pages (there are usually several) and write down or print everything you see. You probably can use the print-screen key for this, but because modern BIOS's use graphics on the CMOS screen expect to see many gibberish characters. Once you have recorded all the parameters, you are safe since you can restore any incorrect parameters.

Now that you can access the CMOS set-up, what can you do there? (There are many different BIOS's, and yours may differ somewhat from this.)

Find out about your hardware - It lists such things as CPU type and speed, cache sizes, video controller type and memory, disk sizes, and sound card type.

Change the boot order - You can set from which disks and in which order your PC will try to boot. I prefer to boot only from the hard disk. On those rare instances when I really have to boot from a diskette or a CD-ROM, I change the boot order only as long as I need it.

Configure the POST - The first thing your BIOS does on boot-up is to run the Power On Self Check. This can be either elaborate or minimal. I prefer minimal since it decreases boot time.

Configure the ports - You can enable or disable your infrared port, configure the printer port (to SPP, EPP, or ECP), and enable or disable the COM ports. Usually you set the printer port to ECP, but you may have to change it if you connect different devices to this port. Internal modems that use the ISP bus use the same addresses and IRQ as one of the serial ports. When you install one, you'll have to disable the appropriate COM port. You will also have to set-up the plug-and-play features to tell the BIOS that it must not try to allocate the addresses and IRQ that the modem uses. See your computer or motherboard manual for the instructions if it isn't clear on the CMOS screen. You have to configure plug-and-play for any non-plug-and-play interface card. Fortunately, these are becoming rare.

Configure a hard disk - When you add or replace a new disk, select the "IDE Auto-detect" feature let the BIOS load the correct parameters. (The wording of this feature may differ for your particular BIOS.) If the disk is very old, you will have to enter the parameters by hand.

Set up power management - Modern PCs can shut down the display monitor and hard disk if you leave them idle. You can set the length of these periods and what happens if they elapse. This is more important for laptops than for desktops, and they can cause problems with some programs. If you experience problems after changing these parameters, just change them back or disable power management altogether.

Set up security - There are two passwords: one is required to run the PC and the other to modify CMOS. Usually both are disabled, but you can set them to keep others from using your PC.

It is not difficult to set up CMOS to reflect your own preferences, and because you can always exit the set-up program without saving changes there is little risk, especially if you've recorded the correct parameter values.



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Tulsa Computer Society 6/02/2003
Don Singleton, President