 NCQ differs from TCQ in that, with NCQ, each command is of equal importance, but NCQ's host bus adapter also programs its own first party DMA engine with CPU-given DMA parameters during its command sequence whereas TCQ interrupts the CPU during command queries and requires it to modulate the ATA host bus adapter's third party DMA engine.NCQ's implementation is preferable because the drive has more accurate knowledge of its performance characteristics and is able to account for its rotational position.Both NCQ and TCQ have a maximum queue length of 32 outstanding commands (31 in practice).