On 02/10/2016 04:09 PM, Tony Harminc wrote: > On 10 February 2016 at 15:50, Joel C. Ewing <[email protected]> wrote: >>> Why do you think that SIE would not continue to provide virtual >>> ESA/390 support? Today, when z/VM is running in zArch mode on the >>> metal on e.g. a z12, it can surely have an ESA/390 mode guest OS. I >>> see no reason that wouldn't continue just because the host processor >>> doesn't IPL in ESA/390 mode. >>> >>> Tony H. >>> >>> >> Well that was sort of my first thought too, but the actual wording in >> z/VM Statement of Direction was that "the IBM z13 server family will be >> the last to support ESA/390 architecture mode", not that it wouldn't >> support ESA/390 mode on IPL. That sure sounds like there will no longer >> be any hardware ability to switch ARCHLVL mode, and that z14 and later >> will run only in ARCHLVL2 mode. > Well I don't know what IBM has actually said, or what they mean, so > I'm speculating as much as you are. Hopefully one of our friendly > IBMers will step in and clarify. But my understanding of "the IBM z13 > server family will be the last to support ESA/390 architecture mode" > is simply that on z14+ the IPL sequence will not start in or pass > through ESA/390 mode, and it will not be possible to issue a SIGP to > set ESA/390 mode. OK, but none of this suggests that a guest under SIE > will not be able to run in ESA/390 mode. Perhaps the IPL will take > some assistance from z/VM, but no one cares if that has high emulation > overhead. > > BTW, this whole "switch architecture modes on the fly" reminds me of > the famous Gordon Letwin "turning the ignition off and back on when > the car's doing 60 MPH" scheme for the Intel 286 on OS/2. Only it's > architected, rather than being a fortuitous kludge. > > http://www.google.com/patents/US4825358 > > Tony H. > > > The announcement for z/VM V6.4 on Feb 16 says (emphasis added): "ESA/390 removal. Enhancements enable hypervisor initialization and termination, SAPL, and stand-alone utilities to run entirely in z/Architecture® mode. The z13 is planned to be the last z Systems server to support running an operating system in ESA/390 architecture mode. All future systems will support only operating systems that run **entirely** in z/Architecture mode."
"In addition, support will be added to simulate a z/Architecture-only environment, by providing a virtual machine environment that is always in the z/Architecture architectural mode and **cannot switch** to the ESA/390 architectural mode. This can be useful for testing software in a **z/Architecture-only environment**, in advance of deploying software on a future z/Architecture-only machine." That seems pretty explicit to me that the plan is that on z14 and beyond an operating system will be required to start and run exclusively in z/Architecture mode and that there will simply be no hardware capability to run in ESA/390 mode, period. I think in this context z/VM must also be classed as an operating system. It is also, I think, significant that the z/VM V6.4 "enhancement" topic is titled "ESA/390 removal", not "ESA/390 future emulation" or "ESA/390 future support". -- Joel C. Ewing, Bentonville, AR [email protected] ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
