duel 2.5GHz CPU = 5GHz? Also, Mac CPU rating Vs PC... how do they compare?

spiers69spiers69
Posted:
in Current Mac Hardware edited January 2014
hey all,

a few questions to do with CPU speeds. Is having a duel 2.5GHz G5 like having 5GHz? Im guessing it is... but as far as i know apple doesnt market the G5 like this, which makes me think otherwise.



also, i know that PCs and Macs are measured differently, for example a 400MHz Mac should be faster than a 400MHz PC, right? But how do they compare? What is a Mac Mhz worth in PC Mhz?



im sure i've made some mistakes here, but if you know what im talking about (because clearly I dont!) then please correct me.

Comments

  • Reply 1 of 5
    lundylundy Posts: 4,466member
    Quote:

    Originally posted by spiers69

    [B]hey all,

    a few questions to do with CPU speeds. Is having a duel 2.5GHz G5 like having 5GHz? Im guessing it is... but as far as i know apple doesnt market the G5 like this, which makes me think otherwise.



    Yeah - if you had a perfectly parallel application, say adding up all the numbers between 1 and 10,000 - then you could code your app to split the addition into 2 threads of 5000 numbers each. Mac OS would automatically use both processors and you would have almost the equivalent of a 5 gHz processor.



    Most apps, however, do not thread themselves like that, as they do not know ahead of time how much CPU time each task takes, and usually tasks depend on the results of other tasks, so it gets complicated.



    The OS does put ITSELF on a different processor from the current task, whenever that is feasible. If you look at the processor graphs while OS X is running, both are being used pretty much evenly balanced. But if an app that wants to compute primes, or do RC5 crunching, starts up, and it isn't written to be multi-threaded, then you will see one processor go higher than the other while that app is running. The OS can still put the single-thread app on the least busy processor each time the app's turn comes to run.

    Quote:

    also, i know that PCs and Macs are measured differently, for example a 400MHz Mac should be faster than a 400MHz PC, right? But how do they compare? What is a Mac Mhz worth in PC Mhz?



    There is no way to compute that accurately or for all applications. In general, the G5 has a shorter pipeline so it gets more done per clock than the Pentium 4. The Pentium makes up for that by having a huge clock rate. But again it depends on the application. Apple is moving to Intel not so much because the Pentium is better NOW, but because IBM and Motorola have basically made plans for the future that do NOT include better processors for desktops or laptops. IBM is going with the gaming consoles and mainframes - graphics specialized processors (Cell), which aren't good for general-purpose computing, and the POWER5 and POWER6, both of which are huge, expensive, and hot, but reliable for large mainframes or blade processors which can be noisy, hot and bulky, and are meant to run with dozens of processors hooked together. Nowhere in IBM's or Motorola's road map is there a cool, lo-power CPU for Powerbooks or a faster one for desktops.
  • Reply 2 of 5
    cdoverlawcdoverlaw Posts: 73member
    Dual 2.5ghz isnt as fast as 5ghz, its hard to explain but from what i know i believe that while having dual cpus will boost perfornance it is only helpful when large cpu loads,
  • Reply 3 of 5
    john.outwaterjohn.outwater Posts: 116member
    Quote:

    Originally posted by cdoverlaw

    Dual 2.5ghz isnt as fast as 5ghz, its hard to explain but from what i know i believe that while having dual cpus will boost perfornance it is only helpful when large cpu loads,



    Multiple processors help when performing many different activites. Like when a server is computing so many different processes it really helps. Ofcource to the average user 2.5 compared to a dual 2.5 will be slower. But it won't be like what a 5GHZ machine would be.
  • Reply 4 of 5
    beigeuserbeigeuser Posts: 371member
    Dual processor 2.5 GHz will never equal 5.0 GHz because there are many overhead processes needed in dual-processor setups. But in an ideal multi-threaded environment it might reach up to the equivalent of 4GHz+ (It depends on how well the two CPUs communicate with each other. I think I read before that PowerPCs are better than AMDs or Intels in a DP setup.)



    Anyway, since no software is thoroughly multi-threaded and hardly any software is completely single-threaded, my personal estimate/average was to multiply the clock speed by 1.5.



    So 2.5x1.5=approximately 3.75GHz.



    BTW, it's hard to compare Mac clock speeds and PC clock speeds because of their different architecture. It's difficult to even compare AMDs to Intels so nearly impossible to compare PowerPCs to Intels without knowing the specific types of software that you are using.
  • Reply 5 of 5
    sunilramansunilraman Posts: 8,133member
    this is random, and may get shot down, but based on your question,



    maybe think of a dual 2.5ghz g5 powermac as similar to a dual-core 3.8ghz Intel or AMD cpu



    that said, maybe you could share what you would like to do with that dual 2.5ghz powermac g5? it will be a FAST beast, seriously...



    the g5 chip, while hot, and IBM has been a bitch getting it's speed up, is a really really great powerPC RISC chip, performance wise. anyone that has used a g5, including iMac g5 owners, will tell you performance wise, it's been stellar.
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