On Thu, 9 Dec 2010 06:23:45 -0700, Paul Gilmartin wrote: >I understand that on z/OS Java has a special dispensation to use >storage within the bar.
I wish you wouldn't write "within the bar". It suggests that the bar has thickness, which it does not. Addresses up to and including 7FFFFFFF are below the bar. Addresses from 80000000 and up are above the bar. "Special dispensation" is not needed. Prior to that, it is true that that IARV64 would never create a memory object in the range from 2GB to 4GB. That was an arbitrary decision intended to avoid confusion. As I understand it, there was some concern that a user might see an address with bits 0-31 all zero and bit 32 on and be confused. Is it a 31-bit address with the high order bit on to signify AMODE(31) or is it a 64-bit address? It seems to me that it hes led to considerable other confusion. As to Java, this was discussed on IBM-MAIN. See, for example, this post from Jim Mulder: http://www.mail-archive.com/[email protected]/msg108339.html where he writes, >>The range from 2GB to 32GB is set aside for a particular >>intended user, which is the JVM. The way that the area is used is described in SHARE presentation 2160 from Seattle last year, titled, "Java SDK5, SDK6 and Beyond: A Performance Update" -- Tom Marchant
