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What is a Data Stack

The Data Stack, known as the Program Stack on z/VM, and as the External Data Queue on other platforms, can be viewed as a scratch pad within memory.

Data items can be added to the Stack in one of two ways, but are only extracted by one:

PUSH - Add to the front, like adding to the top of a pile.

QUEUE - Add to the rear, as with any queuing system.

PULL - Extract from the front, like taking the top item of a pile.

Stack management per se is beyond the scope of this tutorial.