If we go into the evolution of radio technology, then we can say that radio technology has been in evolutionary process. Typically the system is designed and built for operations based on some parameters.
For example there could be a radio system which works only a HF range or in the VHF range, or in the UHF range. One could have a system which uses one or the other modulation scheme, for example we may have a radio system which works on analogue AM, FM, PM, etc., or it works in the digital mode like, say, FSK, QPSK, etc.
We may have radio systems which may accept different data formats. So one would have different kinds of systems and a system which is designed for a HF will not work for in the VHF range or a system which is designed for analogic modulation technique will not work when the modulation technique is digital. Basically what we say is that inter operability is a basic issue.