external data representation (XDR)

External Data Representation (XDR) is located on the representation layer of the OSI reference model and provides a machine, operating system and network independent data structure in the Network File System( NFS).

The XDR data structure supports a set of primitive data types from which the more complex data structures of XDR are composed. The purpose is to enable the exchange of data between computers that work with different data representation. Thus by XDR different notations are adapted to each other or arithmetic operations are unified as for example computations with floating point, which are differently implemented in different computers.

XDR uses an RPC system, Remote Procedure Call; it is similar to the abstract syntaxASN.1 and described in RFC 1014.