Troubleshoot CMOS Errors on PC Start Up - dummies

By Dan Gookin

To troubleshoot your PC when it is experiencing persistent start-up errors, take a look at the words that scroll across the screen on start up to see if the errors say anything about CMOS. If so, it may be a dead motherboard battery.

Yes, your computer has an internal battery. That battery keeps track of the time while the computer is turned off. On ancient computers, it also maintained something called the CMOS (say “see moss”). So a telltale sign of a CMOS error, and therefore a dead PC battery, was that the word CMOS appeared in the error message. For example:

162-System Options Not Set
163-Time & Date Not Set
The following configuration options were automatically updated:
Disk 1: 2428 Mbytes
If you are running Unix, you need to configure your system using the COMPAQ User Diagnostics diskette.
Total memory installed: 98304 Kbytes
Diskette Drives
CMOS checksum invalid, default values loaded
F1: Save Changes Compaq Deskpro 4000

To the trained eye, the information in this start-up text error message says a lot. Don’t concern yourself with those details; just note the line that says CMOS checksum invalid. That’s the clue that the PC needs a new battery.