Turbo and the 15-inch MacBook Pro

The 15 and 13 are different enough that I'll address the two separately. Both are huge steps forward compared to their predecessors, but for completely different reasons. Let's start with the 15.

Starting with Sandy Bridge, all 15 and 17-inch MacBook Pros now feature quad-core CPUs. This is a huge deal. Unlike other notebook OEMs, Apple tends to be a one-size-fits-all sort of company. Sure you get choice of screen size, but the options dwindle significantly once you've decided how big of a notebook you want. For the 15 and 17-inch MBPs, all you get are quad-core CPUs. Don't need four cores? Doesn't matter, you're getting them anyway

Evolution of the 15-inch MacBook Pro Early 2011 Mid 2010 Late 2009
CPU Intel Core i7 2.0GHz (QC) Intel Core i5 2.40GHz (DC) Intel Core 2 Duo 2.53GHz (DC)
Memory 4GB DDR3-1333 4GB DDR3-1066 4GB DDR3-1066
HDD 500GB 5400RPM 320GB 5400RPM 250GB 5400RPM
Video Intel HD 3000 + AMD Radeon HD 6490M (256MB) Intel HD Graphics +
NVIDIA GeForce GT 330M (256MB)
NVIDIA GeForce 9400M (integrated)
Optical Drive 8X Slot Load DL DVD +/-R 8X Slot Load DL DVD +/-R 8X Slot Load DL DVD +/-R
Screen Resolution 1440 x 900 1440 x 900 1440 x 900
USB 2 2 2
SD Card Reader Yes Yes Yes
FireWire 800 1 1 1
ExpressCard/34 No No No
Battery 77.5Wh 77.5Wh 73Wh
Dimensions (W x D x H) 14.35" x 9.82" x 0.95" 14.35" x 9.82" x 0.95" 14.35" x 9.82" x 0.95"
Weight 5.6 lbs 5.6 lbs 5.5 lbs
Price $1799 $1799 $1699

Apple was able to rationalize this decision because of one feature: Intel Turbo Boost.

In the ramp to 90nm Intel realized that it was expending a great deal of power in the form of leakage current. You may have heard transistors referred to as digital switches. Turn them on and current flows, turn them off and current stops flowing. The reality is that even when transistors are off, some current may still flow. This is known as leakage current and it becomes a bigger problem the smaller your transistors become.

With Nehalem Intel introduced a new type of transistor into its architecture: the power gate transistor. Put one of these babies in front of the source voltage to a large group of transistors and at the flip of a, err, switch you can completely shut off power to those transistors. No current going to the transistors means effectively no leakage current.

Prior to Intel's use of power gating, we had the next best thing: clock gating. Instead of cutting power to a group of transistors, you'd cut the clock signal. With no clock signal, any clocked transistors would effectively be idle. Any blocks that are clock gated consume no active power, however it doesn't address the issue of leakage power. So while clock gating got you some thermal headroom, it became less efficient as we moved to smaller and smaller transistors.


All four cores in this case have the same source voltage, but can be turned off individually thanks to the power gate above the core

Power gating gave Intel one very important feature: the ability to truly shut off a core when not in use. Prior to power gating Intel, like any other microprocessor company, had to make tradeoffs in choosing core count vs. clock speed. The maximum power consumption/thermal output is effectively a fixed value, physics has something to do with that. If you want four cores in the same thermal envelope as two cores, you have to clock them lower. In the pre-Nehalem days you had to choose between two faster cores or four slower cores, there was no option for people who needed both.

Now, with the ability to mostly turn off idle cores, you can get around that problem. A fully loaded four core CPU will still run at a lower clock than a dual core version, however with power gating if you are only using two cores then you have the thermal headroom to ramp up the clock speed of the two active cores (since the idle ones are effectively off).

Get a little more clever and you can do this power gate and clock up dance for more configurations. Only using one core? Power gate three and run the single active core at a really really high speed. All of this is done by a very complex piece of circuitry on the microprocessor die. Intel introduced it in Nehalem and called it the Power Control Unit (this is why engineers aren't good marketers but great truth tellers). The PCU in Nehalem was about a million transistors, around the complexity of the old Intel 486, and all it did was look at processor load, temperature, power consumption, active cores and clock speed. Based on all of these inputs it would determine what to turn off and what clock speed to run the entire chip at.

Another interesting side effect of the PCU is that if you're using all cores but they're not using the most power hungry parts of their circuitry (e.g. not running a bunch of floating point workloads) the PCU could keep all four active but run them at a slightly higher frequency.

Single Core Dual Core Quad Core
TDP
Tradeoff

The PCU actually works very quickly. Let's say you're running an application that only for a very brief period is only using a single core. That's more than enough time for the PMU to turn off all unused cores, turbo up the single core and complete the task quicker.

Intel calls this dynamic frequency scaling Turbo Boost (ah this is where the marketing folks took over). The reason I went through this lengthy explanation of Turbo is because it allowed Apple to equip the 15-inch Macbook Pro with only quad-core options and not worry about it being slower than the dual-core 13-inch offering, despite having a lower base clock speed (2.0GHz for the 15 vs. 2.3GHz for the 13).


13-inch MacBook Pro (left), 15-inch MacBook Pro with optional high res/anti-glare display (right)

Apple offers three CPU options in the 15-inch MacBook Pro: a 2.0GHz, 2.2GHz or 2.3GHz quad-core Core i7. These actually correspond to the Core i7-2635QM, 2720QM and 2820QM. The main differences are in the table below:

Apple 15-inch 2011 MacBook Pro CPU Comparison
2.0GHz quad-core 2.2GHz quad-core 2.3GHz quad-core
Intel Model Core i7-2635QM Intel Core i7-2720QM Intel Core i7-2820QM
Base Clock Speed 2.0GHz 2.2GHz 2.3GHz
Max SC Turbo 2.9GHz 3.3GHz 3.4GHz
Max DC Turbo 2.8GHz 3.2GHz 3.3GHz
Max QC Turbo 2.6GHz 3.0GHz 3.1GHz
L3 Cache 6MB 6MB 8MB
AES-NI No Yes Yes
VT-x Yes Yes Yes
VT-d No Yes Yes
TDP 45W 45W 45W

The most annoying part of all of this is that the base 2635 doesn't support Intel's AES-NI. Apple still doesn't use AES-NI anywhere in its OS it seems so until Lion rolls around I guess this won't be an issue. Shame on Apple for not supporting AES-NI and shame on Intel for using it as a differentiating feature between parts. The AES instructions, introduced in Westmere, are particularly useful in accelerating full disk encryption as we've seen under Windows 7.

Note that all of these chips carry a 45W TDP, that's up from 35W in the 13-inch and last year's 15-inch model. We're talking about nearly a billion transistors fabbed on Intel's 32nm process—that's almost double the transistor count of the Arrandale chips found in last year's MacBook Pro. These things are going to consume more power.

Despite the fairly low base clock speeds, these CPUs can turbo up to pretty high values depending on how many cores are active. The base 2.0GHz quad-core is only good for up to 2.9GHz on paper, while the 2720QM and 2820QM can hit 3.3GHz and 3.4GHz, respectively.

Given Apple's history of throttling CPUs and not telling anyone I was extra paranoid in finding out if any funny business was going on with the new MacBook Pros. Unfortunately there are very few ways of measuring turbo frequency under OS X. Ryan Smith pointed me in the direction of MSR Tools which, although not perfect, does give you an indication of what clock speed your CPU is running at.


Max single core turbo on the 2.3GHz quad-core

With only a single thread active the 2.3GHz quad-core seemed to peak at ~3.1—3.3GHz. This is slightly lower than what I saw under Windows (3.3—3.4GHz pretty consistently running Cinebench R10 1CPU test). Apple does do power management differently under OS X, however I'm not entirely sure that the MSR Tools application is reporting frequency as quickly as Intel's utilities under Windows 7.


Max QC turbo on the 2.3GHz quad-core

With all cores active (once again, Cinebench R10 XCPU) the max I saw on the 2.3 was 2.8GHz. Under Windows running the same test I saw similar results at 2.9GHz.


Max QC turbo on the 2.3GHz quad-core under Windows 7

I'm pretty confident that Apple isn't doing anything dramatic with clock speeds on these new MacBook Pros. Mac OS X may be more aggressive with power management than Windows, but max clock speed remains untouched.

Mac OS X 10.6.6 vs. Windows 7 Performance
15-inch 2011 MBP, 2.0GHz quad-core Single-Threaded Multi-Threaded
Mac OS X 10.6.6 4060 15249
Windows 7 x64 4530 16931

Note that even though the operating frequencies are similar under OS X and Windows 7, Cinebench performance is still higher under Windows 7. It looks like there's still some software optimization that needs to be done under OS X.

Introduction What About The 13?
POST A COMMENT

198 Comments

View All Comments

  • Brian Klug - Friday, March 11, 2011 - link

    So I roll with my optical drive replaced with a Vertex 2 SSD inside an OptiBay daily. It's an awesome combination if you can do it.

    One problem I noticed however is that Apple's EFI won't boot optical drives other than their own $79 external drive. That means if you want to use boot camp, you have to install Windows with the optical drive (internal SATA) connected, then do the swap to OptiBay SSD + HDD.

    -Brian
    Reply
  • AmdInside - Thursday, March 10, 2011 - link

    I'm just not that interested in this years lineup. The better CPU performance is nice but given how much more features Windows notebooks provide today, I feel I can rely on Windows notebooks as a desktop replacement much more than I can a Macbook Pro. I will still use my MBP 13 2010 for home use but for business, I rely on my Windows laptop. Reply
  • Braddik - Thursday, March 10, 2011 - link

    Amazing article! I love how thorough and detailed you are. Mad props! I work in a medium-large size organization and the Dell vs. Apple debate is hot right now. Our Mac user base is growing, but the majority of the organization is Dell. I would love an article that compares the performance/value/support of MacBook Pros vs. Dell Latitudes in the Enterprise environment. Which is better? Can/should organizations feasible make the move to a full Mac environment? I would love your input! Thanks! Reply
  • Anand Lal Shimpi - Friday, March 11, 2011 - link

    Thanks for the kind words. I'm not sure I can offer much advice in terms of how the MBPs fare in an enterprise environment. While I know of many corporations that now issue OS X systems as an option, those systems typically have some form of Windows on them (either via Boot Camp or as a VM).

    Perhaps someone else may be able to offer more input?

    Take care,
    Anand
    Reply
  • Chloiber - Thursday, March 10, 2011 - link

    I still think it's too early to completely throw away desktops.
    With my T410, I also made the change to use it as my main "working" computer. At home, I can dock it and use my big, comfortable screen. It's very fast in "normal" usage like simple programming, texting, surfing, some "medium" load graphical stuff, some MATLAB etc. etc. - it's just perfect.

    But as soon as I want to do really heavy stuff like hours of video encoding, I still switch to my desktop with 4 or more cores and a fast dedicated GPU. It's just not the same and I really don't like to stress my laptop that much (allthough it is a Thinkpad). I don't know - I'm even less comfortable with a quad in my notebook. I don't know, but it's just not the same as a Desktop for really heavy stuff.

    I do like the new MacBooks - I don't like the resolution of the 13" model though...it's awful...
    Reply
  • Ushio01 - Thursday, March 10, 2011 - link

    While i expect a Mac Pro refresh late 2011 early 2012 I wonder if it could be the last. With the discontinuation of xserve and as this review demonstrates a mobile CPU matching less than year old server level parts in performance and thunderbolt allowing highspeed access to a NAS box I can see Apple discontinuing there last product targeting solely the professional market and truly becoming a CE company. Reply
  • rural_oregon - Friday, March 11, 2011 - link

    Yes, I have to agree with you. With macs only 20% of Apple's total revenue, and the mac pro only perhaps 5% of the mac revenue, at some point soon it just won't be worth the effort. I think it's even possible that there may not even be a sandy bridge mac pro. Reply
  • tipoo - Friday, March 11, 2011 - link

    It certainly seems like a possibility. Apples focus really has shifted to mobile devices, and its Mac revenues are only about a fifth of what the company makes. I can't imagine the Pro is any substantial percentage of their revenue, 1-5% perhaps. Might not be worth the effort for them. On the other hand, it would irk mac developers and creative pro's. Reply
  • wast3gat3 - Thursday, March 10, 2011 - link

    Just a short thanks for such an in-depth review.
    I have a mid-2010 15" MBP and am upgrading this week to the 2011 15" MBP as the performance gain is just too good to pass up. Interesting though that Apple locks the TRIM support in to their own SSD. I'm still going with the 7200rpm 500GB option and will move that disk to an opti-bay and the 3GB controller now knowing that they are using B3 stepping and fit a 6gb sata SSD. Hopefully LION will fix that TRIM support or some clever cookie works out how to enable it.
    Once again thanks!
    Reply
  • Kuril - Thursday, March 10, 2011 - link

    I always wait for AnandTech reviews because they are almost aways the most comprehensive. I love how the technology behind the reviewed product is summarized, and that there is some footwork to better describe the exact hardware being used (e.g., CPUs for MacBook Pros).

    Thanks for the informative reviews. No one comes close.
    Reply

Log in

Don't have an account? Sign up now