Applies to: @RISK 7.x and Up

How Many CPUs (Cores or Processors) Do @RISK and RISKOptimizer Use?

Default Behavior

When you start a simulation, @RISK estimates the expected run time and uses one or more CPUs to complete the simulation efficiently.

• @RISK 7.x Industrial: Uses between 1 and all available cores, depending on the tradeoff between parallel processing and Excel overhead.

• @RISK 7.x Standard and Professional: Uses no more than 2 cores, regardless of the number installed.

• RISKOptimizer 7.5: Uses multiple cores for parallel simulations during optimizations.

• RISKOptimizer 7.0: Uses a single CPU.

• Project simulations: Use only one CPU.

Controlling CPU Usage

If you want to limit @RISK to a single core:

1. Go to Simulation Settings.

2. On the General tab, set Multiple CPU Support to Disabled.

Multiple CPU Options in @RISK 7.5 and Newer

• Automatic (default): @RISK chooses the optimal number of cores.

  • Industrial: 1 to all cores

  • Professional/Standard: 1 or 2 cores

• Enabled: Specify a number in the #CPUs box; @RISK will create that many Excel copies.

  • Do not exceed your computer’s capacity to avoid slowing down simulations.

• Disabled: Only one core is used.

Beginning with 7.5, Multiple CPU settings also apply to RISKOptimizer optimizations.

Multiple CPU Options in @RISK 7.0

To specify CPU usage:

1. Open Excel Name Manager (Formulas → Name Manager).

2. Define or edit the name RiskUseMultipleCores at the workbook level.

3. Set the value to one of the following:

   • Specific number of cores (won’t exceed your computer’s available cores).

   • all — use all available cores.

   • off — use 1 core.

   • auto — @RISK decides the optimum number of cores.

   • Absolute cell reference (e.g., =$B$12) for dynamic settings.

Defining RiskUseMultipleCores in a workbook overrides the Multiple CPU setting in Simulation Settings.

Technical Notes

• @RISK recognizes as a "CPU" anything Windows recognizes as a CPU. Check your CPU count via Task Manager → Performance.

• Physical cores provide the largest speed improvement; hyperthreaded cores give modest gains.

• Multithreading in Excel is separate from @RISK CPU usage and should generally be enabled for faster simulations.

• System registry values (RiskUseMultipleCores, ForceMultiCore, NumCPU) and Excel name _AtRisk_SimSetting_MaxCores are ignored in @RISK 7.5 and newer.