IBM Mainframe Discussion List <IBM-MAIN@BAMA.UA.EDU> wrote on 11/08/2007 06:23:58 PM:
> No, there is no such 24 bit virtual address. With only 4,096 pages > that are 24-bit addressable, I guess we didn't want to dedicate one of > them for that purpose. > <SNIP> > > Actually, yes. It is address x'000000' and was called PSA (but is > actually absolute page 0). And as I recall, it is always reserved when > you have more than 1 possible CPU on a machine. Actually, no. We are talking about virtual addressability, and x'000000' is certainly addressable as a 24-bit virtual address in every address space, and addresses the PSA for the processor on which the code is executing. Furthermore, absolute frame 0 is also addressable by using the SQA virtual address of the PSA for the processor on which the code is executing. This will reverse prefix to absolute 0. As of z/OS 1.5, if there was more than one CPU available at IPL time, the SQA virtual address of the a PSA will be a 31-bit ESQA address. Otherwise, it will be a 24-bit SQA address. As of MVS/XA, we always use a non-zero prefix for each online CPU, so practically speaking, MVS does not use frame absolute 0 for anything other than IPL processing and SADMP processing (SADMP only uses one CPU and uses a prefix of zero). Jim Mulder z/OS System Test IBM Corp. Poughkeepsie, NY ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
