Please answer the following question: Extract the answer to the question from the following context. Question: What was included in the next wave of computers? Context: Early digital computers were electromechanical; electric switches drove mechanical relays to perform the calculation. These devices had a low operating speed and were eventually superseded by much faster all-electric computers, originally using vacuum tubes. The Z2, created by German engineer Konrad Zuse in 1939, was one of the earliest examples of an electromechanical relay computer.
A:
vacuum tubes