The first bit of the address in the PSW indicates that the address is a
31 bit address. So, there was ambiguity for any address with the first
bit set on.
Was the bit on because it was 31bit code setting the flag, or was it a
real address in 64bit mode?
It was easier to just block out the range as unusable.
Tony Thigpen
Paul Gilmartin wrote on 11/04/2014 06:58 PM:
I know that z/OS STORAGE OBTAIN will never return a block of storage
with 2GiB <= address < 4GiB. But what's the rationale for this?
ISTR that I once knew, but I've forgotten, or always misunderstood.
Is there a superstitious phobia of having bit 32 of a 64-bit
address be 1? If so, isn't 6GiB <= address < 10GiB similarly
offensive? Is it because 2GiB <= address < 34GiB is dedicated
to Java?
-- gil
