> Say, what? z/Architecture machines have 64-bit addressing. It says right > in the Principles of Operation that it can address 16E (16*2**60 == 2**64) > bytes. Putting junk in the high-order bits will get you in trouble right > away.
I suspect that the backplanes have much less than 64-bit addressing - it doesn't make sense to provide more address bits than necessary to address the maximum real storage you plan to attach to the product. However - this level is invisible to the user and all but invisible to the mushware author. Even operating systems like z/OS and Linux/390 can't really see the hardware these days - PR/SM is already virtualising stuff for them. As far as any user at almost any level is concerned, the zSeries is 64-bit at real and virtual levels. Deep underneath it probably isn't, but that's a level that even I am uninterested in. Putting junk in the high-order bits will get indeed the vast majority of people in trouble, because at the level anyone can manage to do this the 64-bit real and virtual mapping will try to honour them. But there's a level deep below where such bits would be notionally ignored. -- Phil Payne http://www.isham-research.com +44 7785 302 803 +49 173 6242039
