POWERとPowerPCの命令セットの話すけど、IBMのJohn McCalpinのコメント
見つけたす。ちなみにこの人わSTREAM benchmarkを作った人すね。
http://groups.google.co.jp/groups?selm=agkcco%24gv4%241%40ausnews.austin.ibm.com&output=gplain
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　　Please note that the old distinction between "POWER" and
　　"PowerPC" is no longer operative. IBM's POWER3, RS64, POWER4,
　　and subsequent processors all implement the 64-bit PowerPC
　　architecture (of which the 32-bit PowerPC architecture is a
　　subset). The RS64 and POWER4 (and following) processors also
　　support the 64-bit PowerPC AS architecture, which includes
　　some additional stuff to make the processor work in iSeries
　　(formerly AS/400) systems.
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つー訳で、>>28に書いたようにバイナリレベルの互換性わ大丈夫す。