Format of array elements in STACKS data segment:

Offset  Size    Description
 00h    BYTE    status: 00h=free, 01h=in use, 03h=corrupted by overflow of
                higher stack.
 01h    BYTE    not used
 02h    WORD    previous SP
 04h    WORD    previous SS
 06h    WORD    ptr to word at top of stack (new value for SP). The word
                at the top of the stack is preset to point back to this
                control block.