Re: AS/400 strong points -Reply

Excerpts from midrange-l: 22-May-97 Re: AS/400 strong points -R.. Danny
McQuestion@vantek. (1782*) 

> Hmmm...  I was under the impression that when you went from a CISC based
> machine (v3r1 or v3r2) to a RISC based machine (v3r7), you had to
> recompile your code. 

If 'compiling' is the process of taking *source code* and producing a
*machine usable format*, then the answer is an unequivocal "No, you
don't need to recompile."   

The reason?  The AS/400 *machine* did not change significantly between
CISC and RISC. 

"WHAT???", you say... "HOW can that BE?!!??  How can you SAY that???"   

It's simply because the AS/400 *machine* itself is an _abstraction_ -- a
non-executable "interface."  When you write assembler code on the
AS/400, you're NOT talking to the hardware, you're talking to a
functional abstraction called the MI. 

So, the Machine Interface (MI) *is* the machine (in an abstract sense),
and it did not change from CISC to RISC (with miniscule exceptions), and
so your existing *machine usable format* is still good. 

Compiling on AS/400 means taking source code and creating the MI
representation of the program (its 'observability'), which *is* the
'machine usable format.'  Again, this format is not directly executable,
and therefore an additional step (called 'translation' or
'retranslation') is required to take the MI (abstract) program form into
the actual hardware-specific instruction set (CISC or RISC or <?>). 
However, this process is architecturally *part of the machine.* 

So, while we shout RISC in great big letters, the bigger (IMO) letters
of _MI_ are what made that possible.  The MI is brilliant, robust, and
enduring design, and I can only hope our users are reaping the benefits
of going to 64 bits without recompiling *from source.* 

I apologize for the fractured nature of this post, and I'm sorry if I'm
ranting -- I spent a few years of my life making sure this stuff works. 
So far it's in pretty good shape.  *8-) 

 ___   _            Blair Wyman (wyman@vnet.ibm.com) / Ph: 507.253.2891 
( /_)  /  _  ' _   Advisory Programmer, Dept GZAA   / TieLine: 553.2891 
_/__)_/_<_/_/_/_' SLIC Program Model, IBM Rochester/ VM: RCHLAND(BLAIR) 
                 Opinions expressed are not IBM's / "SPOOOOOOOOOOOOON!"  





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