Re: OoO execution (was: The Seymour Cray Era of Supercomputers)

On Tue, 20 May 2025 21:21:07 GMT
anton@mips.complang.tuwien.ac.at (Anton Ertl) wrote:

Michael S <already5chosen@yahoo.com> writes:

On Mon, 19 May 2025 06:22:42 GMT
anton@mips.complang.tuwien.ac.at (Anton Ertl) wrote: 

The Pentium Pro (introduced 1995-11-01), HP PA-8000 (introduced
1995-11-02), and MIPS R10000 (introduced 1996-01) are the first
microprocessors which have full-blown OoO execution.
 

>
What about PPC604? It had more limited OoO resources than the 3
processors you mentioned above, esp. fewer numeber of reservation
stations, but it most certainly had reorder buffers, 16 of them.
So, by your own definitions, it should be called the first
single-chip full-blown CPU. 

 
Yes.  The OoO nature with ROB is explained in
<https://arstechnica.com/articles/paedia/cpu/ppc-1.ars/6>.
 
Somehow that did not register with me earlier (even though a collegue
had a Mac with a PPC 604e IIRC).  I guess it's because Apple Marketing
is low on technical details, and if Motorola emphasized this aspect,
that did not pass the filters of the press.  Also, IIRC the
performance was not so exceptional that it would direct a spotlight at
the underlying technology, whereas the Pentium Pro with its suprising
SPECint win certainly did.  Finally, the successors of the 604 (in
particular, the PPC 7450) did not progress much further with OoO
execution

From uArch perspective, PPC/MPC 7xx and 7xxx are really successors of
603 rather than of 604.

The thing closest to microarchitectural successor of 604 (via ill-fated
620) is POWER3, but that one was aimed at completely different market.
An offspring that attempted to re-enter PC processors market was PPC970
(a red-headed little brother of POWER4). This foray was terminated by
Steve Jobs (he always prefer Intel but until this millennium did not
poses political power to impose his preferences on technical team)
lasting for about 3 years.

and still had only mild OoO capabilities at a time when the
Pentium 4 already has a 128-entry ROB (and other structure sizes to
match).  So given the lack of ambition in the 7450, I did not even
think about the possibility that the 604 might have been the first
microprocessor with OoO execution.
 
- anton