This little sketch will give you an idea of how the architecture of a PBX may be configured.
If you get a chance - ask a System Admin to explain the Common Control Shelf to you.|
You will hear a lot of good old telephony/computer terms like: Alogrithms, CPU, Hard Drive, Floppy Drive, Memory, Processing Speed, Switching Matrix, DTMF Generation, Switchover and so on.
I think you will be surprised to learn that the processing power on most PBX's is still in the 386 - 486 mhz range.
You will also come to realize that the main function of a PBX is not to store and output readily accessible data but rather to switch or connect call paths.
Complex data manipulation is still in the Third Party domain.
Remember - most System Admins are not Engineers but a sharp System Admin should be able to tell you the throughput on a shelf Back-plane.
I think you'll be surprised again.