The following message is a courtesy copy of an article that has been posted to bit.listserv.ibm-main,alt.folklore.computers as well.
[EMAIL PROTECTED] (Shmuel Metz , Seymour J.) writes: > PSA is real address 0; it's absolute address 0 for at most one of the > processors in the complex. Neither real nor absolute addresses are virtual > addresses, and the mapping of virtual 0 to real 0[1] is strictly a > software convention. multiprocessor support required a unique PSA for every processor. in 360 multiprocessor, the prefix register (for every processor) contained the "real" address of the PSA for that processor; different processors chose different "real" addresses for their PSA ... so as to have a unique PSA for every processor in the complex. the real, "real" page zero was no longer addressable (assuming every processor chose some other "real" address than zero). this was modified for 370, the prefix register specified the "real" address of the PSA for that processor (as in 360) ... however, if the processor addressed the address in the prefix register, it would "reverse" translate to real page zero. as a result, the real, real page zero could be used as common communication area between all processors in the complex ... and was addressed by using the address in the processor's prefix register. http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/BOOKS/dz9zr003/3.7?DT=20040504121320 from above: 1. Bits 0-50 of the address, if all zeros, are replaced with bits 0-50 of the prefix. 2. Bits 0-50 of the address, if equal to bits 0-50 of the prefix, are replaced with zeros. 3. Bits 0-50 of the address, if not all zeros and not equal to bits 0-50 of the prefix, remain unchanged. ... snip ... #1 & #3 was how things operated in 360 multiprocessor support; #2 was introduced with 370 multiprocessor support (modulo 360 & 370 were 4kbyte pages and above description is for 64bit Z and 8kbyte pages) past posts mentioning multiprocessor support and/or compare&swap instruction http:/www.garlic.com/~lynn/subtopic.html#smp other recent posts in this thread: http://www.garlic.com/~lynn/2007r.html#56 CSA 'above the bar' http://www.garlic.com/~lynn/2007r.html#62 CSA 'above the bar' http://www.garlic.com/~lynn/2007r.html#64 CSA 'above the bar' http://www.garlic.com/~lynn/2007r.html#65 CSA 'above the bar' http://www.garlic.com/~lynn/2007r.html#67 CSA 'above the bar' http://www.garlic.com/~lynn/2007r.html#69 CSA 'above the bar' ---------------------------------------------------------------------- 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
