In both JES2 and JES3 systems, an EXEC COND parameter determines if a step is executed or bypassed. However, JES3 processes all jobs as though each step will execute; therefore, JES3 allocates devices for steps that are bypassed. JES3 will fail jobs that delete a data set in one step and attempt to reference the deleted data set in a later step, even if the step that deletes the data set is bypassed during execution. JES3 does not support conditional JCL, although it does permit conditional statements to be specified.