A 64-bit address is only ambiguous when the high word is zero and the high bit of the low word is on. When the high word is non-zero all 32 bits of the low word can address storage locations without ambiguity.
Chuck Arney Arney Computer System > On Nov 4, 2014, at 6:22 PM, Paul Gilmartin > <[email protected]> wrote: > >> On 2014-11-04, at 17:07, Tony Thigpen wrote: >> >> 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. > Wouldn't that be similarly true for ranges such as 6GiB <= A < 8GiB, > 10 GiB <= A < 12 GiB, ...? Are all such ranges blocked out? > > -- gil >
