IO Pins for Computer like an Arduino
I'm assuming that a computer, which the O.P. has in mind, is an old PC-like desktop or laptop.

There are ways to add microcontroller-style I/O to a computer (old or new).  The class of peripherals that does this is usually called I/O cards or DAQ (data acquisition) card.  The complexity and functionality of these devices varies a lot.  

A good example of a simple I/O card is NI USB-6008.  Another example: an Arduino can be used as a USB I/O card.