Rational Developer for System z
PL/I for Windows, Version 8.0, Programming Guide

/STACK

Use /STACK to set the stack size (in bytes) of your program. The size must be an even number from 0 to 0xFfffFffe. If you specify an odd number, it is rounded up to the next even number.

reserve indicates the total virtual address space reserved. commit sets the amount of physical memory to allocate initially. When commit is less than reserve, memory demands are reduced, although execution time may be slower.

Default: /STACK:0x100000,0x1000

Abbreviation: /ST

Rational Developer for System z
PL/I for Windows, Version 8.0, Programming Guide