Acer Aspire M3400 Service Manual page 29

Frequency/Voltage Control
Parameter
Spread Spectrum
Chapter 2
Description
Enables or disables the reduction of the mainboard's EMI.
Note: Remember to disable the Spread Spectrum feature if you are
overclocking. A slight jitter can introduce a temporary boost in clock
speed causing the overclocked processor to lock up.
Option
Enabled
Disabled
22