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External Data Representation (XDR) is atechnical standard format fordata serialization, for uses such ascomputer network protocols. It allows data to be transferred between different kinds of computer systems. Converting from the local representation to XDR is calledencoding. Converting from XDR to the local representation is calleddecoding. XDR is implemented as a softwarelibrary of functions which isportable between differentoperating systems and is also independent of thetransport layer.
XDR uses a base unit of 4 bytes,32 bits,serialized inbig-endian order; smallerdata types still occupy four bytes each after encoding. Variable-length types such asstring andopaque are padded to a total divisible by four bytes.Floating-point numbers are represented inIEEE 754 format.
XDR was developed in the mid 1980s atSun Microsystems, and first widely published in 1987.[2] XDR became anInternet Engineering Task Force (IETF)Internet Standard in 1995.
The XDR data format is in use by many systems, including:
The XDR standard exists in three different versions in the following RFCs:
