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?
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  • mga318 - Tuesday, June 14, 2011 - link

    Apple just recently released an update for windows and bootcamp that said would provide a performance increase. I'm wondering whether that might of had an effect on Windows gaming since the initial review. Reply
  • macboy123 - Sunday, July 24, 2011 - link

    I have macbook pro mid 2010 with NVIDIA GT 330M and its crashes randomly & frequently (black screen of death).  NVIDIA card on MacBook pro is really CRAP & USELESS!!!!. Reply
  • gradyboy - Monday, August 15, 2011 - link

    I was checking in wikipedia about AES-NI and there was a link to intel site that now revises the info that the i7-2635QM has AES-NI support.

    I think the review should be updated to reflect that.

    link below:
    http://ark.intel.com/products/53463/Intel-Core-i7-...
    Reply
  • edgecrusherr160 - Wednesday, August 17, 2011 - link

    Not sure what the reviewer is talking about with the hinge. I've had a 13 Macbook Pro since Jun 10th 2009 that's seen HEAVY use. It opens and closes beautifully. I appreciate it even more when I use other types of laptops (even older Apples).

    I do agree on the gloss screens, and hate them. I love the fact that there's glass over the screes, really makes them feel solid and protected compared to other laptops. From my experience, no one comes close to the quality of an Apple laptop. I used to work at a computer store too. I wish they made the glass matte though. I have a matte screen protector on mine that distorts the color a little, but I've gotten used to it over the years. Still a shame I have to even use it though.
    Reply
  • abbylegg - Tuesday, August 30, 2011 - link

    Hi,
    Great review really helped out. I'm looking for a macbook pro but everywhere and shop is too expensive.. so i'm trying out freebiejeebies.co.uk which has been proven by The Gadget show, NBC News, BBC news and a couple more big channels and stations. If you would like to help me out on my task trying to get a macbook pro please sign up and fill out a offer for free on this link h t t p : / / g i f t s . f r e e b i e j e e b i e s . c o . u k / 3 8 5 0 2 9 (without spaces just incase this website banes the link) and i promise ill come back and review so you can do the same thing and receive a macbook pro!

    thankyou for your time

    Abby.
    Reply
  • Funkyfreshh8 - Tuesday, October 25, 2011 - link

    Did anyone else notice that in that first picture with the three MBP's stacked on top of each other, the caption says that the 2011 MBP is I the middle, but in the picture it's on the bottom. The one in the middle has a mini-display port, and the bottom one has a Thunderbolt logo instead. Reply
  • MiddletonBanks - Thursday, April 19, 2012 - link

    If you want to transfer big files quickly, have faster boot up and be able to open apps quickly then go for the top of the 15” macbook pro range with the 750GB drive. You can buy it here http://www.middletonbanks.com/acatalog/Apple_MacBo... for only £1,480 including VAT and delivery. Reply

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