On Fri, May 11, 2018 at 9:10 AM, Wayne Driscoll < wdrisc...@rocketsoftware.com> wrote:
> Paul, > Unlike Hercules, z/Architecture is part of a business, and, as such, a > business value needs to be made in order to get support for changes, in > particular radical changes like AM32. "it would be nice" and "but it's so > cool" aren't business rationalizations for the amount of potentially broken > customer code that would result from the change you propose. In order to > not have to recompile all applications, or maintain strict bounds between > 32 bit apps and 64 bit apps like most other 64 bit architectures, I will > gladly sacrifice 2 GiB out of the massive virtual space offorded by a 64 > bit address space. If your mythical AM32 was invented, applications would > still have to switch back to AM31 before calling other AM31 code that > expects a variable length paramter list. I still fail to see any business > value to IBM's customers in what you are proposing. > The real solution is to go back to the 1960s and tell the OS/360 developers to not use bit 0 as an "end of list" indicator. If OS/360 had used either an initial half(or full) word which indicated how many addresses were in the list following or, similar to CMS, had indicated the end-of-list with a fullword of high values (x0FFFFFFFF), then when the architecture was extended to "beyond 24 bit addresses", they could have use AMODE(32) and we wouldn't be having this discussion. AMODE(31) is, IMO, the direct result of this "problem" in the design of OS/360. Of course, the OS/360 design made finding the end-of-list "easier" and did not "waste" a fullword of storage. I guess back in the day, that was a very big consideration. > > Wayne Driscoll > Rocket Software > Note - All opinions are strictly my own. > -- We all have skeletons in our closet. Mine are so old, they have osteoporosis. Maranatha! <>< John McKown ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
