In this tutorial, we explore how a computer adds numbers. We start by taking a look inside the adder, which we have re-constructed using relays. These are electromechanical switches. We explore how the switches form logical components and how they are interconnected to form an adder. Because relays are slow and make clicking sounds, we can both see and hear our adder computing. Enjoy!

In this tutorial, we are building a simple 4-bit computer capable of addition, subtraction, data retrieval and data storage. We learn how to arrange the boards and connect them with power, data and control wires. We program the B4 by entering data into the Data RAM and control instructions (the program code) into the Program RAM. For both, we use the Manual Programmer. Step by step, we then walk through the code and observe how it operates inside the machine.