For reference, any stacks are written as data sets, not stored in memory and are named by using the stack ID, if present, with a .stk extension. The default when no stack ID is present is $mfsstak.stk. A maximum of 32 unique stack IDs are supported. These files are created in the Project's Listing folder.
These files are deleted according to the UNSTACK statement. If the last UNSTACK statement keeps the stack, these files remain on disk. The use of KEEP and DELETE is fully supported.