The earliest monolithic DACs contained little, if any, logic circuitry and parallel data had to be maintained on the digital input to maintain the digital output. Today, almost all DACs are latched and data needs to only be written once, and not maintained. There are many variations of DAC input structures, which will not be discussed here, but the majority today are "double-buffered". A double-buffered DAC has two sets of latches. Data is initially latched in the first rank and subsequently transferred to the second. There are two reasons why this arrangement is useful, the first allows data to enter the DAC in many different ways. A DAC without a latch, or with a single latch, must be loaded with all bits at once, in parallel, since its output during loading may be different from what it was or what it is to become.