NCQ differs from PATA TCQ in that the command re-ordering is performed by the drive rather than the operating system, and each command is equal in importance. This is preferable since the drive has the most knowledge of its performance characteristics, and is able to take rotational position into account. NCQ and PATA TCQ have a maximum queue length of 32 in-flight commands (31 in practice), while SCSI TCQ has a maximum queue length of 2 in-flight commands.