Page "Digital filter" Paragraph 41

The alternate Direct Form II only needs N delay units, where N is the order of the filter – potentially half as much as Direct Form I.

This structure is obtained by reversing the order of the numerator and denominator sections of Direct Form I, since they are in fact two linear systems, and the commutativity property applies.

Then, one will notice that there are two columns of delays () that tap off the center net, and these can be combined since they are redundant, yielding the implementation as shown below.