DH-24AA = MTK
DH-24AY = Optiarc
The third letter in the model number can be:
S = no Lightscribe
L = Lightscribe
So far it seems that:
iHASx24 -08, -09 = MTK
iHASx24 -19, -32, -98 = Optiarc
x=[1, 2, 3, 4]
So far iHAS524 drives seem to be all Mediatek (even the ones ending in -32).
Some HP clones marketed as HP DVD1270i (internal) or HP DVD1270e (external) can also be Optiarc clones (they seem to identify as 1270r in Windows, while the MTK ones seem to identify as 1270d in Windows).