I upgraded my Dos to 3.3 (Zenith)
and started having intermittent lockups.  One of the Model 55SX machines down
the hall was running Dos 4.00 and wouldn't run at all with the driver loaded.
I've tracked it down to a stack overflow.  The default setting for STACKS is
9,128 in Dos 3.3 and Dos 4.00.  When the system is servicing a hardware IRQ,
the stack is only 128 bytes.  Add a Token receive IRQ, and bang, the system
hangs.  You can fix the problem by setting STACKS=9,512 (the 512 is the
important number here).

