The high logical complexity of the out-of-order technique is the reason that it did not reach mainstream machines until the mid-1990s. Many low-end processors meant for cost-sensitive markets still do not use this paradigm due to the large silicon area required for its implementation. Low power usage is another design goal that is harder to achieve with an out-of-order execution (OoOE) design.

A vulnerability in some microprocessor manufacturers‘ implementations of the out-of-order execution mechanism was reported to the manufacturers on June 1, 2017, but which was not publicized until January 2018, …