Performance difference between the 3 available CPU

Discussion in 'MacBook' started by bibyfok, Mar 29, 2015.

  1. bibyfok, Mar 29, 2015
    Last edited: Mar 30, 2015

    bibyfok macrumors 6502

    bibyfok

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    #1
    Hello everyone,

    I think a thread about the 3 CPU options available is important as there is a lot of speculation on if those little boys will be able to sustain good performances.

    First here are the 3 CPU used by Apple.
    [​IMG]

    As wee can see, they frequency and TDP is selectable by the manufacturer, however the turbo boost is chip independant.
    At the end there is only 2 difference:
    • With the entry level, the H5300 is underclocked in comparison to the 2 other versions
    • With the CTO option, the chip has 2 security features that may even not been use by Apple (so this point is irrelevant).
    • The entry level (Core-M 5Y31) has a base frequency of 900Mh with a TDP of 4.5W, but has a max base frequency of 1.1Ghz (the base frequency of the Macbook) and thus will inherit max base TDP of 6W. Thus, the entry level CPU might produce the most heat (as all other would run on "mid-TDP" @ 5W).

    Now let's talk about how the processor behave:
    The CPU is not fan-cooled which means that the dissipation is made thanks to the metal body (Alu?) and thus, even with a very low TDP of 5W, the case might go a bit hot when there are heavy tasks.
    The other point it that because of this cooling method, the CPU will not be able to do intensive task in turbo boost for a long period of time, however it will be super capable of everyday task. (Internet, Office processing, Photo, Video playback etc.)

    On my rMBP I tried to play some heavy MKV to see the CPU usage: I played 3 30Gb+ movies at the same time and my i5 2.6 whas not even used at 20%.
    However, my main concern is when watching streaming videos in HD like on The Verge: The player is in flash and thus a simple HD video was using 60-70% of my CPU. My rMBP was super hot... In the later scenario, the Core M might want to go in Turbo boost to play this which could give a bad user experience as the computer would go a bit hot, and the chip might not be able to achieve a smooth playback experience?

    Should you get the 1.3Ghz CTO? In my opinion NO:
    The normal price for a CTO CPU is between 83€ for a small bump and 190€ for a large one (in France at least). Apple will be probably following this rule and ask for around 100$ for this option.
    When looking at the extremly few benchmark available, the gain of 100Mhz is less than 10% and this is under full CPU load! As I explained, the CPU will not be able to sustain full load for a long time (1 minute max if we are optimistic) and thus the benefits will not being seen in normal usage.
    I would rather recommend the people who want the best "bang for the buck" to stay with the high non-CTO model (1.2/512Gb). That will be my choice! :)

    I hope this post can create a constructive discussion as the CPU capabilities are my main concern and I have passed the last few hours on reading products review that are using Core M chips.

    Edited to add the third point to the list.
     
  2. danielwerner macrumors regular

    danielwerner

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  3. bibyfok, Mar 30, 2015
    Last edited: Mar 30, 2015

    bibyfok thread starter macrumors 6502

    bibyfok

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    #3
    Yes, of course, the higher the multiplier, the higher the temp will be.
    However, given the super low TDP (5W) I don't think we will see a lot of difference between the different CPU, at least nothing really feelable.

    Edit: The entry level (Core-M 5Y31) has a base frequency of 900Mh with a TDP of 4.5W, but has a max base frequency of 1.1Ghz (the base frequency of the Macbook) and thus will inherit max base TDP of 6W. Thus, the entry level CPU might produce the most heat (as all other would run on "mid-TDP" @ 5W).

    900Mhz --> 4.5W
    1.1 Ghz --> 6W
     
  4. Serban Suspended

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    #4
    so what will be the best cpu to buy to deliver the most performance/heat equilibrium ?
     
  5. bibyfok thread starter macrumors 6502

    bibyfok

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    #5
    First we are going to assume that the 5Y31 is the 1.1Ghz processor to be used (99% sure) so it will have a TDP of 6W = most heat generated.

    We also assume that both the 1.2 and 1.3 shares the same TDP (5W). And thus, even if the 1.3Ghz has a higher clock it will delivers the same amount of heat than the 1.2Ghz.

    Lets say you want to do a task that would need 1 seconds to be done on the 1.2Ghz, the 1.3Ghz will take less time to do this task (0.9 seconds?) and thus return to IDLE more quickly = LESS heat.

    My opinion is that theoretically the 1.3Ghz would generate less heat as the task would be computed quickier, however I think this will not be perceptible under normal circumstances... So I will stick with the 1.2Ghz.
     
  6. danielwerner macrumors regular

    danielwerner

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    #6
    But wouldn't a higher clocked CPU throttle down more if it has the same TDP (or in this case, lower than the base model).

    It doesn't make sense that the 1,1 ghz has 1w more TDP than the higher clocked ones. Or can someone explain?
     
  7. bibyfok thread starter macrumors 6502

    bibyfok

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    #7
    Base clock is the throttled clock speed.

    It make sense as those are not the same chip and thus work at different speed and TDP.

    The 1.1Ghz can work from 900Mhz @ 4.5W and up to 1.1Ghz @ 6W --> 1.1Ghz @ 6W
    When the 1.3 can work from 1.2Ghz @ 4.5W to 1.4Ghz @ 6W --> 1.3Ghz @ 5W
     
  8. iRun26.2 macrumors 68000

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    #8
    But if the chips have different energy efficiencies why does Intel not charge more for the more efficient one?
     
  9. Serban Suspended

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    #9
    so my son can play the most demanding game like Crysis 3 on full 1440p for 5 minutes, after that i think the macbook will shut down
     
  10. bibyfok, Mar 30, 2015
    Last edited: Mar 30, 2015

    bibyfok thread starter macrumors 6502

    bibyfok

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    #10
    I have no idea, maybe it's because they priced them to OEM based on the cost of production? But don't worry, Apple will charge you at least 100$ for the speed bump.

    ----------

    TurboBoost on those CPU is not meant to be used for a long time: When a CPU is stressed, it can go from 30°C IDLE to 90°C in a fraction of a second... So do not count on a sustained turbo boost, it will last few second before thermal throttle. Max temp on this CPU is 95°C, as this is a fanless design, I doubt that Apple would allow it to reach that temp.
     
  11. Gav2k macrumors G3

    Gav2k

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    #11
    I honestly think apple will use the higher spec'd chips and underclock to keep the vcore low.
     
  12. bibyfok thread starter macrumors 6502

    bibyfok

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    #12
    5Y71 is the highest Core M available... :(
     
  13. Gav2k macrumors G3

    Gav2k

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    #13
    Correct but it can be clocked to 1.4ghz apple chose 1.3 as the voltage required is lower resulting in better temps
     
  14. bibyfok thread starter macrumors 6502

    bibyfok

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    #14
    Oh yeah, that's what they have done for the 1.3Ghz. You cann see which CPU they have choose when looking at the designed Turbo Boost clock speed.
     
  15. Gav2k macrumors G3

    Gav2k

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    #15
    The turbo Is configurable too so they could choose a faster cpu and down clock for better tdp
     
  16. bibyfok thread starter macrumors 6502

    bibyfok

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    #16
    I highly doubt that as they would have announced the 4.5W designed tdp instead of 5W.
     
  17. Gav2k macrumors G3

    Gav2k

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    #17
    The cpu will offen consume less than this. So it's a mute point.
     
  18. bibyfok thread starter macrumors 6502

    bibyfok

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    #18
    TDP is not a electrical consumption, its Thermal... (Thermal Design Power)
     
  19. leman macrumors 604

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    #19
    Sorry, but its not how it works. The chips are identical. The only difference is that the higher-clocked chips might be of better quality, potentially producing slightly less heat/working more really under load. But that is just a might be.

    There are multiple problems with your argumentation. First of all, base clock is not trotted clock. The CPU can go down much lower than the base clock. Second, a CPU running on its base frequency does not necessarily output its TDP heat. So you can't conclude that the Core-M 5Y31 will produce the most heat. Its simply restricted by its configuration from reaching higher frequencies. Again, this is very individual of course from one CPU die to another one (impurities, fluctuations etc.), but in general, the higher clocked CPUs will run hotter.
     
  20. bibyfok, Mar 30, 2015
    Last edited: Mar 31, 2015

    bibyfok thread starter macrumors 6502

    bibyfok

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    #20
    First of all, I'm not a CPU expert so do not hesitate to correct me if I'm wrong!
    As I can agree with you about the chip design, as often center of a waffer would become high end CPU but it is not for sure how they designed the Core M lineup.

    About the throttled clock, what I wanted to say is that the CPU will never go lower of its based clock under normal usage. The manufacturer can decide to lower Core M base clock to 600Mhz but a "normal" 5Y51 will never go under 1.1Ghz under, again, normal circumstances.

    Regarding the 5Y31 as the max Freq is 1.1 and the max TDP is 6W, I think we can safely assume that his TDP @ that freq will be 6W?
     
  21. Queen6 macrumors 603

    Queen6

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    #21
    I am looking at the 1.2 as I need the 512 SSD, the performance delta is less than the CPU upgrade from the base 1.1 to 1.3, so not as beneficial. I believe the same as the OP the gains in Turbo Boost will be pretty much moot as the MacBook is unlikely to be capable at running full boost for a sustained period of time.

    I recently looked at a Lenovo Yoga Pro 3 the system is reasonably fluid, equally it`s obviously not a powerful machine. Interestingly enough Lenovo opted for a fan which I believe only runs during heavy loads, which implies that the Core M in present iteration will definitely reach temperatures that will induce significant throttling.

    It all comes down to how efficiently the MacBook can cool the CPU, this may well prove to be a double edged blade too slow and the CPU will throttle mercilessly, too efficiently and case may become warmer then one may care for. Let`s face it if the latter is the case the new Macbook wont be the first Apple portable to run uncomfortably hot to the touch ;)

    Another aspect is Skylake is upcoming, I fully expect a new revision of the MB early 2016 and will be upgrading to the new hardware

    Q-6
     
  22. danielwerner macrumors regular

    danielwerner

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    #22
    I don't get it. Why isn't a 1,2 ghz with 256 gb ssd an option?
     
  23. newellj macrumors 601

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    #23
    Probably to keep the SKUs down and possibly also because the performance difference between 1.1, 1.2 and 1.2 gHz isn't enough to be useful? Both are guesses.
     
  24. bjet767 macrumors 6502a

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    #24
    "which implies that the Core M in present iteration will definitely reach temperatures that will induce significant throttling."

    Another ignorant and unfounded statement by someone who wants to slam the new product.

    The truth is this, we don't know how the new rMB will perform under it's max use.

    The truth is the Apple engineers could have solved or reduced the heat issue by internal design thus eliminating the fan. My current 11" MBA rarely turns on the fan and my 2012 Mac Mini i7 Quad core also rarely turns on the fan (normally when using Handbrake).

    Will it get hot? Of course the CPU will get hot (they all do) and knowing this the engineering team (or person) designing the hardware around it took this into consideration. They didn't drop the fan because it was a "cool" (pun intended) idea, they did it because they could.
     
  25. Serban Suspended

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    #25
    I can't wait to get this and play the most demanding game at full resolution and make work in final cut pro at the same time
     

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