XDR is a standard for the description and encoding of data. It is
useful for transferring data between different computer
architectures, and has been used to communicate data between such
diverse machines as the SUN WORKSTATION*, VAX*, IBM-PC*, and Cray*.
XDR fits into the ISO presentation layer, and is roughly analogous in
purpose to X.409, ISO Abstract Syntax Notation. The major difference
between these two is that XDR uses implicit typing, while X.409 uses
explicit typing.
XDR uses a language to describe data formats. The language can only
be used only to describe data; it is not a programming language.
This language allows one to describe intricate data formats in a
concise manner. The alternative of using graphical representations
(itself an informal language) quickly becomes incomprehensible when
faced with complexity. The XDR language itself is similar to the C
language [1], just as Courier [4] is similar to Mesa. Protocols such
as Sun RPC (Remote Procedure Call) and the NFS* (Network File System)
use XDR to describe the format of their data.
