To be honest, if you think of today's digital computer, there's not much of a difference between a digital computer and an analog one, today's digital computers use the same concepts, for instance, memory is stored on chips with matrices of silicon gates, each gate is composed of two layers of silicon, P and N, which interact in a special way that allows for a metaphorical value (the binary 0 or 1) to be stored at said gate, at the bottom line, OFF and ON inevitably become 0 and 1.
With all of the particles involved in this process, you end up using physical particles to represent information.
I'm a big fan of abstract, and even quantum computers use similar techniques for information storage and retrieval, although utilizing a much more delicate property of physical particles, information is stored and retrieved by harnessing the physical properties of the particles themselves, so, you can think of qubits (the quantum computer's equivalent of a bit) as meta-data stored ON a physical particle.
So, in essence, one could argue that you can build a computer out of anything with strict rules of interaction, provided by the right elements, you could build a logic gate out of anything dynamic (which responds to external events and affects surrounding objects in the same sense), even sticks of wood and a water stream serving as current would serve as an adequate (but not optimal) solution, the only problem would be arranging them in the right way.
So, can you use light for this? I bet you could, and photonics are quite close to becoming common place.
Can we use monkeys for this? I BET YOU COULD!
Preface
As outlined above, as long as elements of the system can affect other elements, any chain of events could be considered a form of computing, and as long as a current can turn another current off, you can build a logic gate out of it, and this includes trained monkeys, and a river.
Hardware platform
In this section I'll propose a potential approach to building a CHIMPUTER, and let's begin by defining the term CHIMPUTER, and the hardware architecture: A CHIMPUTER is a closed system with trained MONKEYS and CHIMPS inside, all seated by a stream of water that runs throughout the system, the arms of said monkeys are tied to wooden gates with short ropes, data is transferred through the water stream as BANANAS (or DIGITAL BANANAS for short), and as the first banana enters the stream, the highly trained monkey will try to grab it, pulling the rope in the process, switching gates on and off, and thus interrupting or permitting the flow of a different stream somewhere else.
The rope could also be tied to a BANANA DISPENSER that activates different currents throughout the machine's lifetime.
So, how does computation fall into this? and here we come to the memory, which is stored in matrices of 8BANANA BOXES, divided into small partitions, and placed in a BANANA MAZE, memory addressing is done through the rope pulling of MEMORY CHIMPS that pull the ropes in a specific sequence, influenced by the information carried by the stream of water, thus, opening and closing specific gates inside the BANANA MAZE, through which a highly trained MEMORY CHIMP will navigate and fetch the destination box and then dispatch it to the C-PU.
Same logic applies to the C-PU, the rope-pulling-logic-gates can drive the whole system, for computation, you have the AND-CHIMP, the OR-CHIMP, the ADD-CHIMP, and other specialists trained to process their instructions specifically.
I/O
Input is done using punch-cards, as you'd expect from a top-of-the-line analog computer.
Output: that's my favorite, monkey-with-the-typewriter can press keys based on where the bananas fall.
Of course you'd argue that chimps do all the cool work, and monkeys do the menial tasks, but what can I say, chimps are smarter by nature, and for a successful design, you must not neglect such critical details.
Operating System
The machine will come with a pre-installed copy of MONKEYSOFT® BLINDS©: FIESTA™, a fast, feature-rich, secure, and stable operating system.
Instruction set
The system will include a BASIC-CHIMP to interpret, and natively execute MONKEY-BASIC instructions, MONKEY-BASIC is a powerful, high-level, and highly-structured language with a procedural approach, and a CHIMP-ORIENTED feature set; designed for ease of use and flexibility; and of course line numbers are mandatory, too bad you must use punch-cards to input the program still.
In closing
You can see it, can't you? this technical marvel can (and will, once it goes live), alter the way we think of modern computers, and have a notable impact on everyone's day-to-day life.
Now all I need is adequate funding for my exceptional ideas.