ROTOR makes a lot of chainrings, so it can get confusing! But the differences here can be explained pretty easily.
ROTOR Direct Mount (DM) Rings
Design: The ROTOR Direct Mount Rings chainrings are a one-piece chainring design that saves weight while simultaneously increasing rigidity. Compared to a standard chainring with spider and bolts, the ROTOR DM ring is approximately 30 grams lighter by comparison. In addition, because the ring is made from a single piece of aluminum, rigidity is improved.
Compatibility: These chainrings are compatible with ROTOR’s 2INpower and INpower DM power meters as well as ROTOR ALDHU and VEGAST cranksets
Sizes: They are available in round or oval shapes.
ROTOR 110×4 Chainrings
Design: The ROTOR 110×4 Round Chainrings are traditional 2-piece rings with a separate outer and inner chainring.
Compatibility: These chainrings can fit both 110×4 cranksets (such as Shimano) as well as ROTOR cranks and power meters (by adding the ROTOR 110×4 Spider). In addition, they allow you to more easily change your chainring sizes in the future if you need to. They are available in round or oval shapes.
Sizes: They are available in round or oval shapes.