Arrays in MATLAB 6.5 used to be the same as arrays in current versions of MATLAB. However, as best I recall, "handle" objects were not supported in MATLAB 6.5. MATLAB 6.5 had a completely different method of defining object oriented objects.
Functions in MATLAB 6.5 used to be the same as functions in current versions of MATLAB. However, functions in MATLAB 6.5 did not support arguments processing. Also, in MATLAB 6.5, it was not permitted to have function definitions inside "scripts", and nested functions were not permitted.
Note that there were no free versions of MATLAB; you would need very special reasons to want to use MATLAB 6.5 these days.
On the off-chance that you are interested in more current versions of MATLAB, see
