Controlling generic robot via computer

use controller that supports said number of I/O. normally this would be some kind of PLC.

Well, 600 individual switches would require a minimum 10-bit addressing space. That puts one lower bound on the solution.

How are you connecting to these switches? Do you need to run an ON and OFF wire to each one? Are they on some kind of serial addressable bus?

One extremely crude method would be to run 10 signal wires (plus power&ground) to all 600 switches. And at each switch, wire a unique binary circuit that would respond to only one specific binary pattern on those 10 wires (000000001 for Switch 1, 0000000010 for Switch 2, etc). Then control the binary states of those 10 wires from your computer.

A better method would probably be to run a simple RS485 bus to all the switches, and give each switch a small microcontroller that could respond to addresses and commands across the bus, and generate discrete on/off signals to individual switches. Ideally, instead of 600 microcontrollers, you might use one micro for every 8-16 switches.

But, as Panic says, the "correct" solution would be to utilize COTS hardware made for this, most likely a PLC with an appropriate number of control outputs. And, depending on the physical dispersion of the switches, some industrial bus and distributed I/O modules.

Quote from AspiringMadScientist

Compete beginner's stupid question. What is the easiest way to control a large number (like over 600) of on/off switches (for controlling actuators of whatever kind) via a computer program, presumably assigning each switch a variable?

I never saw a robot job using over 600 actuators

What kind of job has this robot to do?