Atomic operations tagged memory_order_seq_cst not only order memory the same way as release/acquire ordering (everything that happened before a store in one thread becomes a visible side effect in the thread that did a load), but also establishes a single total modification order of all atomic operations that are so tagged.

This type of ordering may be necessary for situations where all consumers must observe the changes being made by other threads in exactly the same order. It requires full memory barriers as a consequence on multi-core or multi-CPU systems.

As a result of such a complex setup, this type of ordering is significantly slower than the other types. It also requires that every single atomic operation has to be tagged with this type of memory ordering, or the sequential ordering will be lost.