Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!ucsd!ucbvax!UMDD.BITNET!BRUCE
From: BRUCE@UMDD.BITNET (Bruce Crabill)
Newsgroups: comp.lang.asm370
Subject: New System/3x0 Instruction
Message-ID: <9103180151.AA14097@ucbvax.Berkeley.EDU>
Date: 18 Mar 91 01:44:23 GMT
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Reply-To: IBM 370 Assembly Programming Discussion List
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I would call an instruction something that was architected and well defined.
These assist microcoded subroutines change as the function in the operating
system that it is trying to implement in microcode changes with new releases.
That is why you have various EC levels of these assists.  CP will check the
EC level of the assists installed and if not at the right level, will
disable the assists.  I think this is the major difference, an "instruction"
is something that the manufacturer has defined to work according to the
Principles of Operations and does not change, whereas a microcode assist
can change at the manufacturer's whim and is not generally documented.  Yes,
there are publically available books that tell you what they do, but they
do not define in Principles of Operations detail exactly what they do.

                                       Bruce