Interesting. I knew that VM had to use some special instructions but not much
more.
Thomas Berg
====== Thompson, Steve (SCI TW) ====== wrote 2006-08-18 17:15:
-----Original Message-----
From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On
Behalf Of Thomas Berg
Sent: Friday, August 18, 2006 8:43 AM
To: [email protected]
Subject: Re: The Fate of VM - was: Re: Baby MVS???
<SNIP>
(I had the impression that there were very little support(ing
developement) needed
for VM, especially compared to MVS.)
Thomas Berg
<SNIP>
IEF (Interpretive Execution Facility) was done for VM to provide the SIE
instruction (Start Interpretive Execution). A super EXecute and
BASR/BALR/BASSM type thing. It is what allows VM to NOT have to shadow
"MVS" any more.
There's some pretty hefty and serious micro-code to implement that. And
because it has gone through at least 3 upgrades (XA to ESA to z/ARCH),
that's quite a bit of support for VM that is not even in CP itself. And
this is on-going development as things about the channel architecture
changes, certain instructions come along (e.g., SCLP - Various of the
B2xx allow you to talk to the service processor -- these have to be
intercepted...) that affect the CEC, etc.
Then there are various instructions that are done just for VM to
dispatch guests that MVS, VSE and TPF don't make use of (at Amdahl we
had various assist instructions that I believe IBM was also doing just
for VM). This is another development area that must be done in
micro-code (does IBM also use vertical micro-code as well as
horizontal?).
So there's more to VM development than one might think.
Lastly, there's PR/SM, which at first WAS VM under the covers (I can't
tell you how many people told us [when I was at Amdahl] about how they
could get into "CP" when running PR/SM). I do not know if PR/SM is still
a flavor of VM. But it makes use of some of those "Hypervisor"
instructions that VM seems to have to know about so that z/OS BCP
developers can do their thing...
Later,
Steve Thompson
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