.beam difference between builds and misc HiPE questions

Matthias Lang <>
Wed Nov 16 23:57:20 CET 2005

François-Denis Gonthier writes:

 > - I just noticed that everytime I build, whatever options I choose,
 > the .beam files are actually changed.  The size is not changed in
 > anyway but there is a small difference on the binary level.
 > What has changed? and most importantly for me, are those files
 > interchangeable between builds?  I suppose the difference is
 > something like a date to differentiate builds but I think it's
 > easier for me to ask this list than dig the internals of .beam
 > files.

Among other things, there's a timestamp (compile-time) in the BEAM
file. You can see the timestamp by evaluating


The files are interchangeable, as long as you don't change Erlang
VM versions.

(Actually, you can use beams made by the an older compiler in a newer
VM for many useful combinations of VM and compiler, but you usually
can't do the reverse.)


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