The main differences between it and the OM10 models lies in that fact it was designed from the the get go as a camera with TTL-OTF Autodynamic metering with built in manual over-ride with the shutter ring around the lens throat just like the OM2 models of which the OM2n came out around the same time rather than relying on the optional manual adapter the OM10 did.
In some respects then it's more a cut down OM2 losing that models TTL-OTF flash metering, the interchangeable focusing screens, backs although it kept the ability to use a power winder .
The focusing screen fitted was brighter than the OM10's and displayed the camera system information in a easier to see and less obtrusive way.
The above picture shows the OM20 in front of 1983's OM30 which Pop briefly owned which in truth was a more a focus confirmation with a 'auto focus' 35-70 zoom version of the OM10 that many found less than reliable at that.
The failure to come up with a truly efficient auto focus SLR in many ways was what lead to Olympus losing it's place in the SLR market and dropping out of making its last film slr, the OM4Ti in 2002.
