< Assuming each relay occupied a cubic inch, one million relays would < occupy a cube 100 inches on each side, or just a bit over 8 feet on each < Not ridiculously large. The problem is not the size of the relay but the wires to interconnect them. For each relay one can assume there would be a minimum 10% volume overhead for interconnecting wires. < Of course, real relays much smaller than a cubic inch are readily availa < and a real computer of that density would have incredible cooling < problems. There are small units in the size of T05 (.325" dia, .265 tall) and the crystal can sizes (1.25x1.00x.375). So small relays are common and their power needs are very small. Also they cycle faster. These relays also have the advantage of being sealed preventing contamination. The later detail is real for larger systems. I have used the crystal can relays for control systems (25 relays!) and they are reliable fast and modest power. the units I used were Allied Signal manufacture and at 26.5v only required 50mA (max) and had 5A DPDT contacts. Each relay would use 1.325W... full scale machine using say 10,000 would use a fair amount of power. There are lower power relays available as well. Using two cross coupled makes a fine flip-flop. Allison