Arduino vs Old Computers
Similar capability in turns of processing power if you compare back 10 -20 years. 

arduino is a micrcontroller not a microprocessor.  

A good example is the pdp11 minicomputer and the ti msp430 micro controllers. They share the same instruction set (approx 90%) . Both can (or could) do realtime event handling but pdp11 was more for data processing. Though pdp11 didn't have integrated peripherals

see bottom of this page http://www.cpushack.com/CPU/cpu4.html