An MDR (Module Description Resource) is just a mini database with text information used to describe the characteristics of an instrument or device.  An MDR can be provided for any instrument module.

A Kmax instrument driver provides the low-level, native code used to communicate between the device/interface and the computer. The MDR for the controller module identifies the driver component which is loaded when the instrument is compiled.   Both are necessary in order to communicate with a external device. MDRs for instrumentation slave modules are not necessary in order to communicate with them via the intrface module, but they make the system easier to setup and use.