Async processors have been around a long time, and some were sold commercially in the pre-microprocessor days. The IAS machine and clones, designed by von Neum

Async processors have been around a long time, and some were sold commercially in the pre-microprocessor days. The IAS machine and clones, designed by von Neumann's team in the 1940s, was asynchronous. A bit later, the PDP-6 and first generation of PDP-10, were too, as well as Honeywell's mainframe processors in the 70s and 80s: > The 6180 processor was among the last of the great non-microcoded engines. Entirely asynchronous, its hundred-odd boards would send out requests, earmark the results for somebody else, swipe somebody else's signals or data, and backstab each other in all sorts of amusing ways which occasionally failed (the "op not complete" timer would go off and cause a fault). Unlike the PDP-10, there was no hint of an organized synchronization strategy: various "it's ready now", "ok, go", "take a cycle" pulses merely surged through the vast backpanel ANDed with appropriate state and goosed the next guy down. Not without its charms, this seemingly ad-hoc technology facilitated a substantial degree of overlap [...] [1] I think it's fair to say it's harder to reason about async logic. And nearly all design tools are today oriented around clocked logic. So asynchronous designs have become very niche (and they were never mainstream). But the basic premise that it is more efficient, is probably true. [1] https://www.multicians.org/mga.html#6180 https://www.multicians.org/mga.html#6180