MSI 645 Ultra-C Manual page 37

Hardware Setup
Jumpers
1
1
3 3
Keep CMOS
Clear CMOS
1
JBAT1
You can clear CMOS by shorting 2-3 pin while the
system is off. Then return to 1-2 pin position. Avoid
clearing the CMOS while the system is on; it will
WARNING!
damage the mainboard.
2-21