When calculating more than one scenario, WEAP can calculate multiple scenarios simultaneously, each in their own separate "instance" of WEAP. Because most modern computers have multiple CPU "cores," each instance of WEAP can run on a separate core, thus achieving a significant speedup over running all scenarios sequentially on a single core. Go to Help, About to see how many CPU Cores your computer has.
Turn on the Use Parallel Calculation? checkbox to activate parallel calculations. (Note :this option is not available in the following circumstances: only one scenario needs to be calculated, your computer only has one CPU core, your WEAP area is linked to LEAP, MODFLOW or QUAL2K, you are doing PEST Calibration or a Safe Yield Analysis. It is not available in the unlicensed evaluation version of WEAP.) Choose the Number of Workers to use. Each worker will be a separate instance of WEAP. To achieve the maximum speedup, you should set this to the number of CPU cores in your computer. Regardless of the setting, WEAP will not launch more instances of WEAP than there are scenarios to calculate.
Note: If you have made any changes to the area, WEAP will automatically save them so that the changes can be copied to the Workers.
When calculations begin, WEAP will launch several new instances of WEAP (the smaller of "Number of Workers" and the number of scenarios to calculate). The original instance of WEAP, the "Manager," will be moved to the left side of the screen, and each new instance of WEAP, the "Workers," will be tiled on the right side of the screen. You will be able to see the progress of calculations in each worker, as well as in the manager. Once all scenarios have been calculated, the Workers will close and the Manager will open the Results View to display the results. If you want to stop the calculations before they are complete, click the "Cancel" button. If WEAP doesn’t hear from a new worker within two minutes, it considers that worker dormant and tries to start another one.