> Yes, but computers are not whats important in calculation. Algorithms are.
That's not correct.
> The physical properties of the computer don't matter in this regard.
That's not correct.
> You could do exactly what a computer does with pen and paper (it would just take a much longer time).
Yes, and that time matters greatly as it's the difference between practical and hypothetical. Beyond that, programs that can evolve their hardware have been shown to come up with optimizations no human could have created and thus the physical properties of the computer do matter.