As a simple example , if we are running code on a 2-processor system ( CPUs `` a '' & `` b '' ) in a parallel computing environment and we want to do tasks `` A '' and `` B '' , it is possible to tell CPU `` a '' to do task `` A '' and CPU `` b '' to do task ` B '' simultaneously ( at the same time ) , in order to reduce the runtime of the execution . As a simple example , if we are running code on a 2-processor system ( CPUs `` a '' & `` b '' ) in a parallel environment and we wish to do tasks `` A '' and `` B '' , it is possible to tell CPU `` a '' to do task `` A '' and CPU `` b '' to do task ` B '' simultaneously , thereby reducing the runtime of the execution .