BSS was a "pseudo-operation" in SAP (SHARE assembly program) for the IBM 704. My recollection is that the assembler manual called it "block starting at symbol". There was also a BES (block ending at symbol) pseudo-op. Both reserved a block of memory, with the assembler assigning the appropriate value to the pseudo-op's label. The reason for BES was that index registers were subtractive. There was a loop-ending instruction ,TIX (transfer on index), that decreased the index by a specified amount and transferred to a specified location unless the index hit zero, in which case the instruction counter continued in sequence. BES was originally conceived for addressing an array stored by increasing subscript but indexed by a register that counted down. BES was also useful for FORTRAN object code, which stored arrays backward and kept the true, uncomplemented subscript in an index register. Doug