%ORACLE_HOME%\bin\orastack.exe

the orastack utility was created to allow users to modify the amount of stack that's reserved and/or committed by each thread in the oracle server.

By running orastack on certain .exe files, the headers of these executables are patched to reflect the settings specified. Typically, changing the commit size of each thread's stack is not necessary, since NT will commit more stack as needed. However, decreasing each thread's reserved size may be necessary since this size comes out of the Oracle Server's 2 gigabyte address space.

When thousands of connections or a large SGA are in use, running out of address space in the Oracle server process [although still having available physical memory in the machine] is a possibility.