SAP HR/HCM – Version differences

Basic SAP differences

Unicode was used from ECC 5.0 and upwards, Upto SAP 4.7 – Nonunicode was used.
4.6C has ABAP stack, 5.0 and 6.0 have netweaver component (Java is additional)
For installing SAP ECC6.0 Solution Manager Key is required. Previously it was not required
Features and configurations were done using the tables directly, in ECC5.0 and upwards, it is dont using the IMG nodes.
Integration with SOA was possible after ECC6.0

Check functionality-wise differences in this link