STACK Segment : The purpose of the STACK Segment declaration is to set aside a block of memory (the stack area) to store the stack. The stack area should be big enough to contain the stack at its maximum size. The declaration syntax is
Where size is an optional number that specifies the stack area size in bytes.
Sets aside 100h bytes for the stack area(a reasonable size for most applications). Is size is omitted, 1KB is set aside for the stack area.