Spool data sets and spooling

Simultaneous peripheral operations online (spool) has several meanings as used in this book and throughout JES2 documentation. Spooling is a process by which the system manipulates its work. This includes:

Using storage on direct access storage devices (DASD) as a buffer storage to reduce processing delays when transferring data between peripheral equipment and a program to be run.
Reading and writing input and output streams on an intermediate device for later processing or output.
Performing an operation such as printing while the computer is busy with other work.

Spool also refers to the direct access device that contains the spool data sets. This definition is generally apparent from the context of its use and should not cause any misunderstanding in the JES2 documentation.

Spooling is critical to maintaining performance in a z/OS-JES2 environment. JES2 attempts to maximize the performance of spooling operations, which ultimately benefits the throughput of work through the JES2 installation. As noted previously, spooling provides simultaneous processing and a temporary storage area for work that is not yet completed. When JES2 reads a job into the system, JES2 writes the job, its JCL, its control statements, and its data to a spool data set until further processing can occur.