What is a Computer?

Ben Brubaker has a new Quanta essay Does Computer Science Need Computers? 

Despite the title (and authors generally don't choose their titles), Brubaker's essay really addresses the question as to whether computer science is about computers. He starts with Dijkstra's apocryphal quote "Computer science is no more about computers than astronomy is about telescopes."

This is the wrong analogy: computers are not the telescopes, they are the stars. You just have to use a broad definition of computer.

The word "computer" goes back to at least 1613. The etymology

1. Latin com- meant “together.”
2. Putāre meant “to reckon” or “calculate”—and originally “to prune” or “clear up.”
3. English added -er, meaning “someone or something that performs an action.”

The word originally meant one who computes, usually referring to a human performing a computational task. Its meaning as a machine didn't come into wide use until the mid-20th century. 

I start off every undergraduate theory class I teach with the question "What is a Computer", even in my Foundations of Complexity posts. After some discussion we end up with a diagram like this.

A Computer

The computer doesn't need to be electrical, mechanical or biological. You can think of the postal service delivering a letter based on an address, an auction arriving at a price, or even a well that draws water as we pull a rope. 

The Church-Turing thesis says the process can always be represented by a Turing machine, and then we are off to the races.

When theoretical computer science stops talking about computing, it just becomes mathematics and no longer computer science. If we want to keep it computer science, we need a computer at the center, some kind of process.

How about the title "Does Computer Science Need Computers?" No, not for electronic computers, though they've become more helpful, especially in this AI era. But doing research in computing is a process in itself. Alan Turing drew inspiration for his machine from thinking about how a mathematician works. So yes, you need a computer for computer science, and a computer for astronomy and every other discipline, even if that computer is just yourself.