Define storage.
labelDSexpression
The DS directive reserves a block of memory, the length of which in words is equal to the value of expression. This directive causes the runtime location counter to be advanced by the value of the absolute integer expression in the operand field. The expression can have any memory space attribute. The block of memory reserved is not initialized to any value. The expression must be an integer greater than zero and cannot contain any forward references (symbols that have not yet been defined).
S_BUF DS 12 ; 12-byte buffer