On Thu, 25 Feb 2016 07:39:30 +0100, Peter Hunkeler wrote: >The 8 KiB area at absolute 0 is the place where the hardware writes >status information as result of performing the "Store Status" operation.
Among other things. Those Assigned Storage Locations are defined by the architecture. Other areas within the PSA are defined by the operating system. >It has existed for longer than PR/SM. I would say, it is owned by the hardware. >> There is Absolute addressing, real addressing, and virtual addressing. > >But wait a minute, isn't there on more level? Absolulte, real, and >virtual are *within* an LPAR. It is required to support multi-CP >operating system *instances*. Since PR/SM, each LPAR must have its >own "absolute address 0", doesn't it? Yes. >Actually, the requirement has exited since physically partitionable CECs >had been in place (can't remember exaxtly which were the first such >machines, 3033, or 308x, or?). Probably System/360 model 65MP. For sure model 67. >The net would be: Some code is accessing virtual address 0. The DAT >feature will (with the help of the DAT tables) translate virtual 0 to *a* >real address (which just happens to always be real frame 0 in z/OS). >The hardware will recognize an address within the "prefixing area" (8 KiB >in z/Architcture, 4 KiB in ESA/390 and predecessors, 2 KiB in even earlier >architectures?), System/360 Principles of operation has described prefixing all the way back to the -0 level of the manual. You can find it at http://bitsavers.trailing-edge.com/pdf/ibm/360/princOps/A22-6821-0_360PrincOps.pdf The description is on page 18, under "Multisystem Feature". It is described there as a 4K area. Before the -4 level of the System/370 POO in 1974, the SET PREFIX instruction was defined. It was not in the -0 edition. -- Tom Marchant ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
