Future G4/G5 scaling?

Posted:
in Future Apple Hardware edited January 2014
Does anyone know how the future PowerPC processors will scale? Right now I understand that Motorola is adding to the pipeline to achieve higher clock speeds (which would mean the G4 doesn't scale all to well).



AMD and Intel both have scallable CPUs while from what I know MIPS and UltraSparcs don't scale all to well either. With Intel I know that they added a phat pipeline in order to be able to achieve 10 ghz but it's supposedly not as effective on a per clock basis.



How will the 7500/8xxx scale? Is the PowerPC trying to catch up mhz wise at all cost or will they use an AMD-like rating? AMD was scaling by short 66mhz steps with the AthlonXP, could Apple do likewise?



Also, do you think that it's be wise to have Fast, Faster, Fastest rating for the Macs and simply putting the current low, mid and high clock speed CPU into them? So that they wouldn't be announcing every 33 mhz step but simply put the currently fastest availible CPU in the top Macs.

Comments

  • Reply 1 of 8
    thttht Posts: 3,980member
    <strong>Originally posted by xype:

    Does anyone know how the future PowerPC processors will scale? Right now I understand that Motorola is adding to the pipeline to achieve higher clock speeds (which would mean the G4 doesn't scale all to well).</strong>



    For every fab process that reduces the size of the chip in half (or 30% reduction in transistor size) there will be about 50 to 100% increase in clock rate from the previous fab process size, depending on the microarchitecture of the chip.



    For example, a 7450 processor fabbed at:



    0.18 micron reaches 1 GHz

    0.13 micron reaches 1.5 GHz

    0.09 micron reaches 2.25 GHz

    ...



    How much that rate increases depends on the agressiveness of the fab. Moto's fabs are dirty, so they have a relatively difficult time. And Moto isn't into the higher Watts for higher clock game much anyways.



    <strong>AMD and Intel both have scallable CPUs while from what I know MIPS and UltraSparcs don't scale all to well either. With Intel I know that they added a phat pipeline in order to be able to achieve 10 ghz but it's supposedly not as effective on a per clock basis.</strong>



    Scalability is more dependent on the process technology than the microarchitecture of the processor. All processors will or should increase in clock rate 50 to 100%, with the appropriate circuit tuning, for every 30% reduction in transistor size.



    <strong>How will the 7500/8xxx scale? Is the PowerPC trying to catch up mhz wise at all cost or will they use an AMD-like rating? AMD was scaling by short 66mhz steps with the AthlonXP, could Apple do likewise? </strong>



    We have no idea what MHz any hypothetical PowerPC chip will clock in it. I doubt Moto or IBM will catch up with AMD in clock rate unless they want to sell a 70 Watt processor.



    <strong>Also, do you think that it's be wise to have Fast, Faster, Fastest rating for the Macs and simply putting the current low, mid and high clock speed CPU into them? So that they wouldn't be announcing every 33 mhz step but simply put the currently fastest availible CPU in the top Macs.</strong>



    It's marketing. Who knows what works.
  • Reply 2 of 8
    powerdocpowerdoc Posts: 8,123member
    [quote]Originally posted by xype:

    <strong>Does anyone know how the future PowerPC processors will scale? Right now I understand that Motorola is adding to the pipeline to achieve higher clock speeds (which would mean the G4 doesn't scale all to well).



    AMD and Intel both have scallable CPUs while from what I know MIPS and UltraSparcs don't scale all to well either. With Intel I know that they added a phat pipeline in order to be able to achieve 10 ghz but it's supposedly not as effective on a per clock basis.



    How will the 7500/8xxx scale? Is the PowerPC trying to catch up mhz wise at all cost or will they use an AMD-like rating? AMD was scaling by short 66mhz steps with the AthlonXP, could Apple do likewise?



    Also, do you think that it's be wise to have Fast, Faster, Fastest rating for the Macs and simply putting the current low, mid and high clock speed CPU into them? So that they wouldn't be announcing every 33 mhz step but simply put the currently fastest availible CPU in the top Macs.</strong><hr></blockquote>



    this is the 64 000 * question, some times ago here on AI some rumor said that it will scale at 1,6ghz in the begining.



    One thing is sure about the G5 it will be a 0,13 micron SOI chip. It's mean that like THT said , even with the same basic architecture than the 7450 it can scale at 1,5 ghz in the beginning. If the G5 have a deeper pipeline it will be able to scale higher.

    However i doubt that we will see a PPC chip with a deeper pipeline than the G4, the PPC chip have choose a different direction than the P4 chip, P4 chip are designed for very high clockspeed and huge data transfer, the PPC chip are designed for high power per clock cycle, low consumption, but not very high clock speed.

    I will add that for the moment we do not know what is the limiting factor of clockspeed for the 7455 chip, i mean is there some exucution unit that can be clocked faster than other (for example is the FPU unit less clockable than the integer unit ?) The answer to this question can give you some clues about the G5 design.
  • Reply 3 of 8
    agent302agent302 Posts: 974member
    I have a curious question: does anyone know what the max multiplier for the G4 is? I mean, a bus improvement seems likely, but if it doesn't happen, what's the highest the G4 could go on a 133 Mhz bus?
  • Reply 4 of 8
    2.13GHz
  • Reply 5 of 8
    agent302agent302 Posts: 974member
    [quote]Originally posted by Nostradamus:

    <strong>2.13GHz</strong><hr></blockquote>



    So, from that I assume that 16x is the max. Thanks!
  • Reply 6 of 8
    spartspart Posts: 2,060member
    If they don't put a faster bus in before the chip reaches 1.5GHz it will just be too laughable...



    The current situation is already laughable...
  • Reply 7 of 8
    *l++*l++ Posts: 129member
    Max speed for the 7445/7455 for 133Mhz bus is 2GHz (15x bus ratio).



    I doubt there ever will be a greater bus ratio.

    IMHO the curent G4 will be pushed no further than 2GHz. There is no point having such a fast CPU on such a slow bus.



    It will be G5 with RapidIO beyond that. With a 400Mhz bus (16bits, double pumped), the G5 will be much better for high speeds.
  • Reply 8 of 8
    cdhostagecdhostage Posts: 1,038member
    d00dz! 400 Mégáhúrtz sééstym bóos!
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