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Subject: Re: Introducing "No-Moore's Law"

Author: Robert Hyatt

Date: 20:29:48 03/11/03

Go up one level in this thread


On March 11, 2003 at 20:17:57, Jeremiah Penery wrote:

>On March 11, 2003 at 12:22:09, Robert Hyatt wrote:
>
>>On March 10, 2003 at 19:56:12, Jeremiah Penery wrote:
>>
>>>On March 09, 2003 at 22:10:06, Robert Hyatt wrote:
>>>
>>>>Did you see an advertisement where someone was trying to convince you to
>>>>buy over the other?  I doubt it.
>>>
>>>When P3 and P4 existed concurrently, every single ad where Intel advertised the
>>>P4, they were trying to get you to buy P4 over P3.  Of course they didn't
>>>explicitly say so, but I don't ever remember seeing an AMD ad where they
>>>explicitly mentioned an Intel chip either.  The P3 was, for many things, faster
>>>than the higher clocked P4.  Intel prematurely killed the P3 because they wanted
>>>to sell P4s, and P3 could have made P4 look bad.
>>
>>You are arguing this from the _wrong_ side.
>
>??? You asked if I'd ever seen an ad where Intel tried to convice me to buy a P4
>over a P3.  I answered that question - every single ad Intel made for the P4 was
>trying to get you to buy it over the P3.


Again, that isn't the point.  I asked where Intel had tried to get you to buy
a PIII instead of a PIV.  They haven't.  And _any_ PIII program will run on a
PIV, so the compatibility in that direction is 100%.



>  No, they didn't specifically mention
>the P3, but the AMD ads never specifically mentioned an Intel processor either.
>


The magazine ads I saw _did_ mention the Intel chip by name.  The headline
was "why pay more?" (again, not an exact quote but but that was the gist)
and later "the K7 is faster and cheaper."  (another non-literal quote).




>>The PIV is 100% compatible with the
>>PIII.  The inverse is _not_ true, and this is often referred to as "backward
>>compatibility".
>
>I gave one example earlier of where P4 is not 100% backward compatible.


Where?  IE what can I do on a PIII that will fail on a PIV?





>
>>That is _different_ than their trying to sell a PIII and saying it is equal to
>>the PIV but
>>much cheaper.  And that case is closest to the K6 vs PII point.
>
>I'm not sure what exactly you're trying to say.


Trying to sell the PIV instead of the PIII is logical.  The PIV will
execute all PIII code.  It is faster.

The K6 vs PII was not so clear, as the K6 would definitely _not_ execute
all programs that run on a PII.




>
>>>>Again, it depends.  If I do a target=P3, I would expect that to run on a PIV.
>>>
>>>If I do target=Pentium, I'd expect it to run on a K6.  That's basically the
>>>comparison you're making there.
>>
>>No, I bought a PII and did "target=pentiumII" because _ knew_ that the PII had
>>different optimization isues than the original pentium.  The PII had an OOE core
>>for example, while the original pentium depended on the compiler to pair
>>instructions
>>for the super-scalar execution units.  At the time I bought a PII, AMD was
>>advertising
>>their chip as faster and cheaper.  And it did _not_ say (but not 100%
>>compatible) and
>>that led to the confusion I mentioned.
>
>You said, "If I do a target=P3, I would expect that to run on a PIV."
>I replied "If I do target=Pentium, I'd expect it to run on a K6."
>
>Is that not a fair analogy?  I'm not sure where the rest of your paragraph came
>from, but it's pointlessly obfuscating.
>


Yes.  But that isn't what we are doing.  I'm interested in buying a PII.
I buy one.  I compile for it and say target=pentiumII.  A friend buys a
K6 and assumes it is compatible with the PII since it is marketed as a
faster/cheaper replacement.  The code doesn't work.

I have a PIII.  A friend buys a PIV.  My target=PIII program will work
perfectly for him.  I wouldn't assume a PIII will do everything a PIV
would do, but the inverse is logical as Intel makes that claim.  I'm used
to the idea that a newer version will be compatible with the older version,
plus adding some new features.




>>>>And most likely if I do a target=p4 it would run on a P3 although I can
>>>>certainly think of reasons why it wouldn't.
>>>
>>>Most of the time it would, just as most of the time K6 would run P2 executables.
>>> The only difference I'm aware of (for K6/P2) is CMOV.  For P3/P4 the difference
>>>is SSE2.
>>
>>But _if_ you compile for the PIII it will absolutely run on the PIV.  If you
>>compile for
>>the PIV it will run on the PIV but perhaps not on the PIII depending on the
>>instructions
>>the compiler is capable of producing.  However, _nowhere_ did you see Intel say
>>"The
>>PIII is 100% compatible with the PIV".  You will find "The PIV is 100% backward
>>compatible with the Pentium processor product line."
>
>Point me to something where AMD specifically mentioned compatibility in terms of
>the _P2_.  Nowhere did you see AMD say "The K6 is 100% compatible with the P2".
>


No, they just said "we are faster and cheaper than the PII."  With the
implication that all else is "equal".  It isn't.  (or wasn't).




>>>>But Intel doesn't market the P3 to be compatible with the P4.
>>>
>>>No.  They market P4 to be compatible with P3.
>>
>>Playing word games.  "backward compatible" is not "compatible".
>
>Just a couple paragraphs ago, you wrote, "The PIV is 100% compatible with the
>PIII."  Before you accuse me of playing 'word games', don't play them with your
>own writing.

I believe I also used the term "backward-compatible" pretty clearly.  I'm
not playing any word games.  _anything_ that works on a PIII will execute on
a PIV, unless instruction timing is critical.  That _is_ compatible in the
definition of "backward compatible".




>
>>look at their ads.  It's very clear what they are saying and what it means.
>
>I think it's pretty clear what Intel's ads were trying to get across, but
>apparently not, since you disagree.  As far as any ads for the K6, I guess it's
>a matter of interpretation as well.


Apparently so...



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