POSIX規格(IEEE Std 1003.1-2001)では定式化されたメモリモデルを定義しない。

A.4.10 Memory Synchronization
Formal definitions of the memory model were rejected as unreadable by the vast majority of programmers. In addition, most of the formal work in the literature has concentrated on the memory as provided by the hardware as opposed to the application programmer through the compiler and runtime system. It was believed that a simple statement intuitive to most programmers would be most effective. IEEE Std 1003.1-2001 defines functions that can be used to synchronize access to memory, but it leaves open exactly how one relates those functions to the semantics of each function as specified elsewhere in IEEE Std 1003.1-2001. IEEE Std 1003.1-2001 also does not make a formal specification of the partial ordering in time that the functions can impose, as that is implied in the description of the semantics of each function. It simply states that the programmer has to ensure that modifications do not occur "simultaneously" with other access to a memory location.

The Open Group Base Specifications Issue 6, IEEE Std 1003.1, 2004 Edition