> -----Original Message----- > From: IBM Mainframe Discussion List > [mailto:[EMAIL PROTECTED] On Behalf Of Paul Gilmartin > Sent: Thursday, November 10, 2005 12:24 PM > To: IBM-MAIN@BAMA.UA.EDU > Subject: Re: How much real is required for 64-bit > >
<snip> > I'd guess the "twilight zone" is virtual; I'd hope the system design > wouldn't squander 2 GiB of real storage (or are the sockets between > 2GiB and 4GiB simply left empty; no DIMMs installed?) > > Does something, then, have a problem with real addresses with the > sign bit set? What? What software is so concerned with real > addresses other than OS memory management, which should have been > thoroughly tested at other sites by now? > > -- gil > -- As best as I can tell, the 2Gib to 4Gib "twilight zone" is strictly virtual and a z/OS only "twilight zone". The problem is the fact that putting the high order bit of an AMODE(31) address "ON" is an "end of list" indication when using the standard linkage conventions. The "twilight zone" is 0x00 00 00 00 80 00 00 00 to 0x00 00 00 00 FF FF FF FF because of the question of "how do I interpret these addresses?" Are they actually address between 2Gib and 4Gib, or are the below 2Gib addresses with the high bit set for "end of address"? The z/OS designers simplified this by simply x'ing out this area. I guess that is why it is called "above the bar". The "bar" is 2Gib in size. There is nothing in the hardware itself, as I read the zPOPS, which "dislikes" those addresses. -- John McKown Senior Systems Programmer UICI Insurance Center Information Technology This message (including any attachments) contains confidential information intended for a specific individual and purpose, and its' content is protected by law. If you are not the intended recipient, you should delete this message and are hereby notified that any disclosure, copying, or distribution of this transmission, or taking any action based on it, is strictly prohibited. ---------------------------------------------------------------------- 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
