> Nevertheless, absolute 0 is owned by PR/SM, right? The 8 KiB area at absolute 0 is the place where the hardware writes status information as result of performing the "Store Status" operation. 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. ... and for practical purposes absolute and real addressing are the same, except when takling about the 8 KiB at real address 0 and the 8KiB point to by the prefix resigsters. 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? 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?). 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?), and will translate real 0 (with the help of the Prefix Register) to absolute 0 (for this LPAR). Some other part of the hardware needs to translate "absolute 0 of this LPAR" to a *physical* memory address (how this works in detail is far beyond my knowledge). -- Peter Hunkeler -- Peter Hunkeler ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
