>> well, if you take the TeX Live CD, there are 213 LaTeX packages with
>> at least 1 file, maybe several. Say 500 files; if
>> you do \usepackage{foo}, at a minimum you have to scan the tree
>> containing those 500 files to locate foo.sty. Is that good or bad?

Let's leave this to one side for the moment, because the next case
is easier to analyse"

>> Then again my CD has over 5000 tfm files. If I do
>>  \font\foo=foo.tfm
>> you are going to have to look at all of them, arent you? hard to see
>> how to cut that down rationally.

If there are only TFM files in the tree, then VMS will be as efficient
as any other system in locating a particular file; if the tree has
other files in it, then unacceptable delays may occur.  It was really
this area for which I was seeking clarification: is TDS defined in
such a way that there is a TFM tree, a TEX/LaTeX tree, and so on,
or are the trees conflated in some way?

>> Whether the tree has irrelevant files depends, of course, on how well
>> you specify the subtree to look at.

It depends even more on what the TDS specifies!