The Base
SAS engine and other engines are able to process several tasks concurrently.
For example, you can enter statements into the Program Editor at the
same time that PROC SORT is processing a large file. The reason that
this is possible is that the engine enables task switching.
Task switching is possible
because the engine architecture supports the ability to start one
task before another task is finished, or to handle work asynchronously.
This ability provides greater efficiencies during processing and often
results in faster processing time. The ASYNCHIO system option controls
this activity.