By June 1948 the Baby had been built and was working. It was in length, tall, and weighed almost . The machine contained 550 valves (vacuum tubes)—300 diodes and 250 pentodes—and had a power consumption of 3500 watts. The arithmetic unit was built using EF50 pentode valves, which had been widely used during wartime. The Baby used one Williams tube to provide 32 by 32-bit words of random-access memory (RAM), a second to hold a 32-bit accumulator in which the intermediate results of a calculation could be stored temporarily, and a third to hold the current program instruction along with its address in memory. A fourth CRT, without the storage electronics of the other three, was used as the output device, able to display the bit pattern of any selected storage tube.