The old one? ALL archived threads are old - no? Are old threads now permanently impervious to response?
Technically, the old style threads are stored as HTML files, each new post causes the file to be rewritten (with the new post appended near the end.) This system was terribly difficult to keep backed up, as any change to any thread would require an archive of the entire thread, which meant on a daily basis hundreds of megabytes would need to be backed up when only a few megabytes actually changed. It also would not work well in an environment where the forum was spread out over several different servers (fault tolerance) which is something I intend to implement later.
The new system has all posts stored in a database, which is easy to "replicate" (backup.) Only the few kilobytes of data that change with each post needs to be backed up, instead of the multi megabyte threads in their entirety. And accessing these posts and adding new posts to threads across a network is trivial. As it stands, I could easily (matter of minutes) change the forum to work with FR's second machine if the first needed to come down for repairs. And eventually, I would like a software program to automatically change over to the second machine if the first one dies unexpectedly.