Biggest differences in terms of underlying foundation are that .classic uses perl only in CGI binary mode, not built into the server like mod_perl would be. Threads, on the other hand, uses PHP which most often is built into the server. It can be run as a CGI binary mode, but usually is not. That difference is huge. If .classic was built to run mod_perl it would have been easier on the server, but not at all portable.
Next, because .classic also was built to be incredibly portable, this it was built on flat text files. It had to load many files as data, more in later versions as it got more features. Some of those text files got quite large and could get corrupted if the server was overwhelmed with too much I/O. Part of what made the later versions of .classic feel slow and heavy was all the work that was put into it to prevent data corruption.
Threads is built on a MySQL relational database which is faster and easier on the server as you scale. It's less likely to corrupt as well. It still can have it's corruption or index problems, but is less likely to have them. MySQL can also be tricky to tune as your site gets larger, but it is able to be tuned pretty easily, where a flat file system really can't without some major voodoo and with less positive effect.
Last edited by David Dreezer; 07/21/2008 2:55 PM.
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