In almost every IBM-compatible computer, there's a ticking time bomb that can turn an expensive machine into an expensive paperweight.
It struck my friend Sid last week.
"The computer doesn't work," he told me over the phone.
"Can you give me a little more detail?" I asked.
"When I turn it on, it says CMOS X-SUM ERROR, or something like that. Then it just sits there."
"Sounds like your battery ran out," I told him.
"Battery? What battery? The daggone machine's been plugged into the wall for two years now."
That may well be, I told him, but the nasty little secret is that every computer with an 80286, 80386 and 80486 processor depends on a small battery plugged into the motherboard, or main circuit board.
The battery powers a chip that contains the computer's clock and a small package of memory made from a Complementary Metal Oxide Semiconductor, known in the trade as CMOS.
This CMOS RAM contains your computer's setup, or configuration data. When you turn your computer on, it looks to the CMOS to find out what kind of disk drives and video board you have, the amount of conventional and extended memory, and a lot of other arcane information about your motherboard that it needs to get running.
When that battery dies, as it inevitably will, the setup information dies with it. Your computer won't work, and you'll get the kind of cryptic message that Sid saw, along with a message telling you to run the computer's setup utility program.
Many computers sold three to five years ago are at the end of their battery life now, resulting in a lot of terrified owners.
"There's hardly a day goes by that we don't get one in the shop," said Richard Cohen, technical director of Micro Repair Services in Towson.
Fortunately, a dead CMOS battery doesn't qualify as a real disaster. You haven't lost any data on your hard disk. Your computer just doesn't know how to find it. By replacing the battery and running the setup program to restore the configuration data in CMOS RAM, you can get your computer working again.
Unfortunately, this is not a job for the faint of heart or the technically challenged. If you're not interested in opening your computer or fooling around with strange setup menus, take your machine to your dealer's service department or a repair shop. Micro Repair Services charges $18 for the battery and $45 for the installation and setup, which is about average.
In fact, given the hassles I've gone through when CMOS problems have cropped up, $45 is downright cheap.
If you're trying to do it yourself, or you're helping someone else, the most difficult part of the job is figuring out what kind of hard drive you have, so that you can enter the information in the setup program.
It doesn't do any good to tell the computer you have a 120-megabyte drive; it needs much more specific information.
When IBM developed the setup program for its original AT computer, it allowed for 46 different types of drives, which
seemed like plenty in the early 1980s. The drives were classified by the number of heads, cylinders and sectors (if you're getting glassy-eyed here, remember that a service department isn't far away). Those 46 drive types remain enshrined in almost every PC today, although few new drives fit into any of those categories
If you have an older computer, the instruction manual that came with it may tell you what drive type to use (1 through 46). On newer machines, the manual may tell you to use a type 47, or user-defined drive, which means you'll have to manually enter the number of heads, cylinders and sectors the drive contains.
If you don't have this information, you'll have to find it. The manufacturer's technical support department can provide it -- if you can get through. On-line services, such as Compuserve, often have listings of drive specifications in their hardware forums (that's where I found Sid's information). A repair shop may also be able to help if it's well-stocked with technical manuals.
All of this sounds like a lot of trouble, and it is. You can minimize the hassle by running your setup program before your battery dies and writing down everything you see on the screen, even if you don't understand what it means. Don't make any changes. Just run the program and restart your computer. The information will make it much easier for you or whoever else tries to restore the machine if the battery dies, or even if you decide to replace the battery before it drops dead.
The job is easier if you have DOS Version 6. A utility program called MSD (usually in your DOS directory) will scan your entire system and provide all the setup information you're likely to need. Print out the results and keep the report in a safe place.
While I was prowling Compuserve in search of Sid's disk drive setup information, I found an interesting set of utility programs that will write the entire contents of your CMOS RAM to a file on a floppy disk. If your battery dies, you can start your system from a floppy and automatically restore the CMOS to its original state. The file, called CMOS14.ZIP, is in Library 4 of the IBM Hardware Forum.
By the way, Mr. Cohen advises every computer owner to make a "boot disk," a formatted floppy with a copy of the operating system and critical files, such as CONFIG.SYS and AUTOEXEC.BAT. If your battery runs out, or something happens to your hard drive, you can always start the machine from the boot disk and then run a utility such as the CMOS restoration program.
He also recommends replacing the CMOS battery every two years, even if you're not having problems. In my experience, most batteries last a bit longer than that, but given the amount of hassle a dead battery can cause -- always at the worst possible time -- the money is well spent.
Michael J. Himowitz is a staff writer for The Baltimore Sun.