Chapter 15 Unified Threat Management for FortiOS 5.0 : Intrusion protection : Configure IPS options : Configuring the IPS engine algorithm
  
Configuring the IPS engine algorithm
The IPS engine is able to search for signature matches in two ways. One method is faster but uses more memory, the other uses less memory but is slower. Use the algorithm CLI command to select one method:
config ips global
set algorithm {super | high | low | engine-pick}
end
Specify high to use the faster more memory intensive method or low for the slower memory efficient method. The setting super improves the performance for FortiGate units with more than 4GB of memory. The default setting is engine-pick, which allows the IPS engine to choose the best method on the fly.