This directory contains executables (binary) which are operating system
specific. Certain SSW IDL SW may only function if the executable for
your specific machine is available here (might check standard places first,
like '/usr/local/lib').

Subdirectories are named by the tags of the IDL !version system variable.

For YOUR machine, the SSW bin directory is:
   concat_dir(concat_dir('$SSW','bin'),!version.OS + '_' + !version.ARCH)

Example
On MY machine...

IDL> print,concat_dir(concat_dir('$SSW','bin'),!version.OS + '_' + !version.ARCH)
/ssw/bin/OSF_alpha
 
In fact, I am going to write a function right now called: "ssw_bin.pro" 
which returns the above value.  That way, the apprproprate executable may
be accessed via concat_dir(ssw_bin(),'programname')