Library routines are addressed through index register XR3. Instructions contained a 12 bit operand, either fixed or offset from an index register. Its core differed from the original 6502 in the lack of the Y index register. Thirty-five patents resulted from the computer and the successful implementation of an index register. For n=0, this turns into a "load index register value into accumulator" instruction. The Index Register is set to N. NAR 2 has instructions to initialize the value of particular index register ("PIR" mnemonic). The instruction set was a single-address type with an index register. The early computers of IAS machine design had no index register. The first three bits after the sign specified an index register. The 6800 had two 8-bit accumulators, a 16-bit index register, and a 16-bit stack pointer. Incrementing the index register to walk the array byte-wise takes only two additional cycles. Some instructions refer to the different bytes in the H&colon;X index register independently.