On 02/10/2016 11:21 AM, Ed Jaffe wrote: > On 2/10/2016 9:05 AM, R.S. wrote: >> W dniu 2016-02-10 o 17:03, Mike Schwab pisze: >>> On a z14, you won't be able to run OS 2.9 or earlier, or 31 bit Linux. >>> Not even under z/VM. >> Well, I wouldn't call it big problem, especially when compared to >> bunch of 31-bit COBOL programs in use. ;-) >> BTW: LPAR profile in HMC still offers "ESA/390" Mode. No, there is no >> "z/Arch" mode. ESA/390 is the choice for z/OS. >> (details are more complcated, but IMHO not relevant here). > > You bring up a good point, Radoslaw. This future hardware change has > nothing whatsoever to do with addressing mode. > > Today, a machine always IPLs in ESA/390 mode (ARCHLVL=1). Operating > systems that prefer to run in z/Architecture mode (ARCHLVL=2) will > switch to that mode as part of early IPL. > > On the new machines (after z13), ESA/390 mode is no longer supported. > IPL will *always* occur in z/Architecture mode so modern operating > systems won't need to explicitly switch modes to function properly. Of > course, IPLs for older operating systems that still require ESA/390 > mode will fail. > > As we know, z/Architecture machines can run 24, 31, and 64-bit > programs. That's not going to change. > Now I see the light -- had forgotten about the whole ARCHLVL-mode switch thing going on under the covers. This effectively also rules out the possibility of any z/VM on a z14 or later being able to provide ESA/390 support to any Virtual Machine as well, since there many significant differences (register sizes, prefix area, privileged instructions behavior, etc) when running z/Architecture mode, and with CP's in that mode the only way to achieve ESA/390 behavior when the hardware no longer supports it would be grossly inefficient emulation. The change in addressing mode at IPL is a minor issue compared to all the other hardware semantic differences from the ARCHLVL mode change. Any 31-bit operating system must of necessity be written for ESA/390 semantics and is not going to run in z-architecture mode, which expects 64-bit addressing and has different hardware instruction semantics!
-- 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
