Originally posted by barkmonster
can these things do multithreading? I know power4's can't which is one reason they ship two chips on one die. Also if not I hope HOPE they release duals.
You mean Hyperthreading It's the OS that handles multithreading.
Well, actually, multithreading is a valid CPU term as well. It means that a CPU can handle multiple threads across its pipeline stages (ie, stage 1 may be Thread1; stages 2-4 may be Thread2; stage 5 may be Thread1 again, etc) ... while this is obviously less usefull in a wide/short pipeline like the G4, it is a very useful technology for countering memory latency in longer-pipeline CPUs.
Hyperthreading, or SMT, is essentially a refinement of multithreading, allowing multiple threads across a specific pipeline stage (ie, the FPU Stage 1 may be Thread1 while the int units' Stage 1 may be Thread2, etc).
SMT is an extra bump in processor efficiency in that it both counters memory latency issues as MultiThreading, and also keeps all pipelines fed as close to 100% of the time as possible.
To answer the previous question: I've not seen anything indicating that the 970 supports multithreading
or SMT/hyperThreading, and such an advance would be odd considering that its "big brother" Power4 does not support either technology either. However, the "Power5" is slated to support SMT in all its glory (reportedly more efficient than Intel's first-gen hyperthreading implementation), and the scant rumors around a "980" tend to agree that HT is being designed into the 980 as well.
I think Apple have backed themselves into a corner with the dual cpu thing. It's the only way they've had any hope in hell of competing with PCs over the past few years, Mac owners have had several generations of dual models to upgrade to.
Imagine someone who's stayed high end for a few years but only upgraded when there's been a significant increase in speed from doing it.
Dual 500Mhz G4 -> Dual 1Ghz G4 -> Dual 1.42 Ghz G4
The next one would logically be dual n Ghz PPC970. It wouldn't matter if it was only a 1.6Ghz dual, it would be significantly faster than the current top of the range dual model just from the bandwidth increases alone.
Well, two things.
First, the 970 gets a lot of its performance increase from the fact that it has a nice, fat FSB going to it, that is quite true. It has four times the memory bandwidth than any G4 to date.
How does that compare to dual G4s? Well, the 970 has an increase in core efficiency which will, combined with a modest frequency bump, give the user the same raw power s their dual G4s,
but the real kicker is this: a single 970
still has four times the memory bandwidth of dual G4s!
So, a single 970 would be "enough" to justify a top-of-the-line machine, and though it may be hard psychologically for some to accept it, the rational side should be able to overcome. Question is: can Apple go the extra step and make it a dualie?
The problem here is that the 970's architecture demands a single FSB per chip, which means the SC chip now has to support not just one FSB but two. Where "dual G4s" were essentially "free" from the design perspective ("cheap' is probably the better word), dual 970s are not.
On the other hand, dual 970s would indeed offer a 75-90% performance improvement in many scenarios (dual G4s tend to average out around 25-30% improvement over singlies), because it keeps that big fat pipe going to each chip without compromise (granted, they still both share the SC-memory bandwidth, which is likely to be less than the sum of two full-speed FSBs).
In essense, with the 970s, Apple moves more into the Intel-like pricing structure regarding dual processors. They perform great, but they are expensive. I'm not sure if Apple will put itself that high up on the performance/price ladder.
That's why there are so many Switchers, whether you choose to believe it or not.
