The Z3 had a binary memory unit, a binary floating point processor, a control unit, and input and output devices. Figure 1 shows the building blocks of the Z3 computer. The binary unit stored up to sixty-four floating point numbers. The floating point representation is comparable to the current IEEE 754 standard. The program was kept on a punched tape and the instructions were coded using eight bits on each row of the tape (Rojas, 2000). There were three types of instructions: memory, input and output, and arithmetic operations which relied on telephone relays; 600 relays for the arithmetic unit, 1,400 relays for the memory and 600 relays for the control unit (“First Relay Computer”, nd). There was a special keyboard for entering instructions. The instructions on the punched tape could be placed in any order and the Lu and Ld instructions stopped the machine. This gave the operator time to enter a number or note the results and then continue with the program (Rojas, 1997). The Z3 contained sixty-four memory words loaded into two floating point registers, called R1 and R2. Rojas points out: “The first load operation in a program (Pr z) transfers the contents of address z to R1; any other subsequent loading operation transfers a word from memory to R2” (Rojas, 1997, p. 8). Once the final instruction is executed, the processor resets to its initial state.