筆者らが1990年代から提唱しているMBCF(Memory-Based Communication Facility)は受信側のメインCPUによる受信割り込み時にメモリ操作まで処理を完結するRDMA等の特殊な機構を必要としない分散共有メモリ環境構築手段である．メモリ操作は必ずメインCPUによってなされるため，異なるアドレス変換方式が混在する問題が発生しない．また，同じ理由から同期を取る方法も単純になる．さらに，複雑な不可分処理もノード間に跨るロックが不要になりロックフリーに行える．これらの意味において，筆者らはMBCFが一定の条件下で定性的に究極の通信同期機構であると考えている．本稿では，MBCFのこの定性的究極性について論じる．

MBCF (Memory-Based Communication Facility), which the authors have been developing since the 1990s, can generate an efficient distributed shared memory environment that does not require special mechanisms such as RDMA, and completes processing target user memory operations by the end of a reception interrupt. Since memory operations are always performed by the main CPU, problems with mixed address translation mechanisms do not occur. Also, for the same reason, the method of synchronization becomes simpler. Furthermore, complex atomic operations can be performed lock-free as there is no need for locks across nodes. In this sense, the authors believe that MBCF is qualitatively the ultimate communication synchronization mechanism under certain conditions. This paper discusses this qualitative ultimateness of MBCF.