Archived from groups: comp.sys.ibm.pc.hardware.chips (
More info?)
In article <TlWkc.7010$Ia6.809665@attbi_s03>,
anonymousjoe@net.net says...
> "Robert Redelmeier" <redelm@ev1.net.invalid> wrote in message
> news:6RUjc.3959$0j3.1020@newssvr23.news.prodigy.com...
> > Paul Tiseo <tiseo123.paul456@mayo.edu> wrote:
> > > If you spend umpteen million in R&D to design the P4, and the P-M
> > > comes along with less R&D and runs slightly faster in some scenarios,
> > > what do you do? Chuck all your P4 R&D out the window?
> >
> > Actually, I believe the Pentium4 was done as a rush job,
> > on the cheap after it became apparant that ia64 (aka
> > Itanium) would not take over. IMHO it's an original
> > Pentium plus SSE2, deeply pipelined for inflated clocks.
> >
> > The Pentium-M is little more than the venerable P6 core,
> > tweaked and clocked higher on smaller processes.
> >
> > -- Robert
>
> It does seem as though the P4 is just that. A P3 with SSE2, with very long
> pipelines (extended further thanks to Prescott) for a hyper-inflated clock
> speed that eventually is pretty decent, but only when you get to a
> ridiculous level of clock speed, and some of that is due to the quadrupled
> bandwidth bus speed combined with the memory speeds (dual channel anyways).
> As the P4 increases in clock speed, so does the L1/L2 cache, which can only
> help but improve performance further.
Yikes! The architectures are *vastly* different. THe P4 has no
integer multiply (has to send the data to the FPU, across chip)
and has no barrel-shifter. The architectures of the
PPro/PII/PIII and P4 are *vastly* different!
>
> What strikes me is that a P4 @ 3GHz is generally on par with an Athlon
> 3000+, which depending on the bus speed chosen is either 2.16GHz (333Mhz
> bus) or 2.1GHz (400Mhz bus).
Sure, because the micro-architecture is *vastly* different.
IFAIC the P4 is a failure in micro-architecture. Maybe they'll
improve it by shoring up it's weaknesses, but so far it is a dud.
> I forget off-hand how deep the P4 pipeline is,
> but is something like 24, isnt it? The Athlon is something like 12, or 15.
> Either way, the numbers are off, but it still is rather close. The P4 has
> L1 & L2 cache running at 3GHz, while the Athlon's is about 66% of that, but
> more plentiful. The bus bandwidth of the P4 is going to be either
You're missing a lot of other details here.
> 4.27GB/sec or 6.4GB/sec (533 or 800MHz bus [yet it is really 133 or
> 166MHz]). Yet the Athlon is using a 3.2GB/sec bus. As for memory, the most
> you can get out of the Athlon is the 3.2GB/sec (whether you use P3200 RAM,
> any speed dual channel RAM, even PC3200), but with P4 you have a shot at
> getting a theoretical of 6.4GB/sec (dual channel PC3200).
Now, consider latency. Bandwidth isn't everything. Bandwith
only takes money, latency takes physics.
> All this combined, things sure look favorable for P4.
Only because you're not looking at the right problem.
> It has so much more
> bandwidth in every area, cache, bus, and RAM. Yet, how come with a 900MHz
> core clock lead, it is only able to tie the Athlon?
See above.
> It seems like it is
> using all the bandwidth and wasting it. If AMD could get the sort of
> bandwidth that Intel has, I would imagine that the P4 would need about a
> 1200MHz or more head start to start being comparable.
Bandwidth isn't a useful measure, unless you don't have enough.
Latency is *always* a useful measure.
>
> For anybody who cares, I do use AMD, so if you want to say I'm promoting AMD
> unfairly or whatever, that's wrong, I'm simply showing that Intel isn't
> efficient.
If I were to buy a system for encoding video and *only* that
function, I'd likely buy a P4. For anything else, forget it. As
you've noted Intel has gone down the wrong path.
<rdh> ;-)
--
Keith
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