Prelude: Two Months with a MacBook Pro

A year ago I tried the notebook as a desktop experiment. The first Arrandale MacBook Pros hit the market and I thought, why not give two cores and four threads a try. I gave it a try for less than a day before having to switch back to the Mac Pro.

Try number two came earlier this year, with the Sandy Bridge MacBook Pro. Twice as many cores and much faster ones at that seemed to be a better recipe for success. Indeed they were. I switched from an 8-core Mac Pro to a 4-core Sandy Bridge MacBook Pro and have stuck with it for two months now.

By the end of this month alone I will have been in the air for 90 hours. Normally I'd have to frantically copy articles, benchmarks, notes and other important documents between machines before I left home for my next flight. Being able to pull an all-nighter testing, grab my notebook and head to the airport without worrying whether or not I forgot to copy something over is pretty sweet.

Regrets? I do have a few.

First, this thing isn't quiet. While my Mac Pro had beefy heatsinks and fans that spun so slowly you could count their fins, the MacBook Pro is a thermally constrained platform. Correction, it's a thermally constrained platform that's always running way too hot. It doesn't matter if the display lid is open or closed, my fans are always annoyingly audible. A lot of this has to do with my workload, I just always have things open that keep the CPU just busy enough that the fans need to work harder. It's frustrating.

Next is GPU performance. I was an early adopter of a multi-monitor setup, but ever since 30-inch displays hit the market I went back to a single display. I never really used the second display enough to justify its existence, it just made me less productive given my workload (I'm more efficient if everything I need is on a single physical screen vs. darting my eyes between two displays). The only complaints I had about 30-inch displays were unimpressive pixel density and a large desktop footprint. The new 27-inch panels started to address those concerns for me so I made the switch last year.

Despite having the upgraded AMD Radeon HD 6750M with 1GB of dedicated GDDR5, the 15-inch MacBook Pro just isn't fast enough to drive the 2560 x 1440 external display when playing most modern games. Even Portal 2 slows down a bit if I'm looking through a portal. Not to mention that the discrete GPU running full tilt causes temperatures to hit their highest and the fans to really spin. I have other machines for gaming and my work computer is mostly for work so this isn't a deal breaker, but it's definitely annoying.

Third, and this is more an issue with Apple's software and not the MacBook Pro hardware, there's still no Quick Sync support in iMovie. As a result all of my video encoding is done on four Sandy Bridge cores instead of eight Nehalem cores in my old Mac Pro. Hmph.

I have other complaints like the sad state of full disk encryption under OS X today since I'm more paranoid about physically losing my data with a notebook. Apple still doesn't offer any support for SSDs with real time hardware encryption so I'm left physically segmenting my data and waiting for Lion. Oh and there aren't enough USB ports. Despite my issues and other than gaming/video encoding, performance isn't an issue. Sandy Bridge is quick and my overall experience is generally quicker than the Mac Pro. Other than video encoding I don't run any heavily threaded applications so a quad-core CPU is the sweet spot for my workload.

Does the added portability make up for the downsides? When I'm traveling a lot - absolutely. It's just so much more convenient. In between trips? Well, that's when it's a lot easier to tempt me back to a desktop.

A couple of weeks ago, this arrived:

It's the new 2011 upgraded 27-inch iMac. More or less it's the 2011 MacBook Pro mated to a 27-inch LED backlit Cinema Display. It's basically my setup but in an all-in-one desktop.

I never liked the iMac. I understood the appeal, but it wasn't for me. The CPUs and GPUs weren't fast enough, there weren't enough drive bays and the display was always worse than what I already had on my desk. However the same series of events that allowed me to dump the Mac Pro and use a Sandy Bridge MacBook Pro have made the iMac that much more interesting.

Moore's Law (or more specifically, hundreds of super smart process and chip engineers) have more or less solved the performance problem in these integrated machines. We've been on the longest run I can remember of software being outpaced by hardware and as a result machines like the iMac look a whole lot more powerful than they did just a few years ago.

SSDs and very high capacity mechanical drives fixed the storage problem, while the advent of 27-inch high resolution LCD panels fixed the display problem. The new iMac can easily be a real workstation for users today, when in the past it was more of a machine you'd give to your parents. To be honest, after using it for a while, I actually like the new iMac.

Two Models

Apple offers two iMacs: a 21.5-inch and a 27-inch model. Just like Apple's notebook strategy, the iMacs are fairly similar in terms of components but primarily differ in screen size/resolution. Of course the larger the screen the higher the likelihood that you'll be doing more with your iMac and thus Apple offers some faster component options in the 27-inch models.

At each screen size Apple has two pre-configured versions: a base and an upgraded model. The upgraded models typically have more upgrades available to them (faster CPUs, faster GPUs, etc...) while the base models are more fixed in their configuration (memory and storage are mostly configurable regardless of system).

Apple sent us the high end 27-inch iMac, which other than its larger display looks like a 21.5-inch iMac with one extra Thunderbolt port. Both systems have four USB 2.0 ports (no USB 3.0 until the Ivy Bridge iMac next summer), audio line in/out, one FireWire 800 port and a Gigabit Ethernet port. There's also integrated WiFi (802.11n) and Bluetooth.

As always, Apple's PC competitors typically win the spec game - particularly when it comes to memory and storage:

All-in-One Comparison
	Apple iMac 21.5-inch	Dell Inspiron 2305	HP TouchSmart 610xt	Apple iMac 27-inch
CPU	Intel Core i5-2400S (2.5GHz quad-core)	AMD Athlon II X4 610e (2.3GHz quad-core)	Intel Core i5-2400 (3.1GHz, quad-core)	Intel Core i5-2500S (2.7GHz quad-core)
GPU	AMD Radeon HD 6750M (512MB)	ATI Radeon HD 5470 (1GB)	AMD Radeon HD 5570 (1GB)	AMD Radeon HD 6770M (512MB)
RAM	4GB DDR3-1333	8GB DDR3-1333	6GB DDR3-1066	4GB DDR3-1333
Storage	500GB 7200RPM HDD	1TB 7200RPM HDD	1TB 7200RPM HDD	1TB 7200RPM HDD
Optical Drive	8x SuperDrive (DVD±R DL/DVD±RW/CD-RW)	Blu-ray Combo Drive (BD-R, DVD±RW)	Blu-ray player & SuperMulti DVD burner	8x SuperDrive (DVD±R DL/DVD±RW/CD-RW)
Display	21.5-inch 1920 x 1080	23-inch 1920 x 1080	23-inch touch enabled 1920 x 1080	27-inch 2560 x 1440
Price	$1199	$1149	$1219	$1699

With the exception of the entry level 21.5-inch iMac, Apple always gives you 4GB of RAM (2 x 2GB DDR3-1333) SO-DIMMs and a 1TB HDD. The entry level iMac keeps the 4GB of memory but drops you down to a 500GB HDD.

Dell is significantly slower on the CPU and GPU side, while HP gives you a faster CPU and somewhat slower GPU. Both Dell and HP give you 50 - 100% more memory and twice the HDD capacity for roughly the same cost as Apple's 21.5-inch iMac. The big advantage however is that HP offers even cheaper machines, the TouchSmart line starts at $629.99.

Apple has never been a value player and the fact that the entry level iMac is at least within the same range as a comparable HP or Dell is pretty impressive. The 27-inch iMac is tempting as the display alone is worth $999. For the base 27-inch iMac that means you get a Sandy Bridge Mac integrated for only an additional $699. That's downright Dell pricing.

The big issue with all-in-ones of course is the lack of upgradability. It's arguably even more of an issue when your all-in-one has a pretty sweet 27-inch 2560 x 1440 panel. I've always kept displays through several upgrades, but you can't really do that with an iMac. I'm not really sure how to come to terms with that aspect of what Apple is offering here.

The smartphone and tablet revolution has finally kicked the display makers into high gear. I'm hoping it's a trend and not a fad and that we will see aggressive roadmaps for larger panels as well. So if replacing your 27-inch panel in a couple of years isn't a big deal then the iMac upgrade path isn't quite as painful. Either way, whoever gets your hand-me-downs will get a pretty sweet display.

The CPU Selection

Like the 2011 MacBook Pro upgrade, the iMac gets the Sandy Bridge treatment. Given the heat-dissipating volume of the iMac's all-in-one form factor, Apple only offers a quad-core CPU throughout the lineup. Just a couple of years ago quad-core CPUs weren't mainstream but I believe today it's safe to say that four cores are going to be the standard going forward. We'll see two cores stick around for small form factors and budget systems but everything else is moving to four. Intel is still toying with the idea of 6-cores for the high end but I'd say there's likely even less traction for 6-cores today than there was for 4-cores a few years ago. While high end desktop users could easily make the argument for 4 cores, it's much more difficult to do the same for 6 unless you're building more of a workstation.

I've described Sandy Bridge several times in the past so I won't belabor the advantages here, but the advent of aggressive turbo modes basically rids the OEM of any reason to make a trade off between more cores and higher clock speeds. Sandy Bridge offers you the best of all worlds - high clock speeds in lightly threaded applications or more cores when you need them.

The iMac is less TDP constrained than the MacBook Pro so we get higher base clock speeds to begin with. In fact, Apple opts for lower priced desktop CPUs than the mobile chips. They are clocked higher and put out more heat but they do help Apple maintain that healthy profit margin. Take a look at Intel's price list:

2011 iMac Comparison
Mobile CPU	Price	Desktop CPU	Price
Intel Core i7-2820QM (2.3GHz quad-core)	$568	Intel Core i7-2600 (3.4GHz quad-core)	$294
Intel Core i7-2720QM (2.2GHz quad-core)	$378	Intel Core i5-2400 (3.1GHz quad-core)	$184

The $2199 15-inch MacBook Pro comes with a 2.2GHz mobile Core i7, the 2720QM to be specific - the CPU itself costs $378. The $1999 27-inch iMac comes with a 3.1GHz desktop Core i5-2400, the CPU here is priced at a much lower $184. The most expensive CPU you can buy in the 27-inch iMac is a Core i7 2600, which Intel charges $294 in 1,000 unit quantities. There's physically more hardware in the iMac, but using desktop CPUs is a no brainer for Apple here.

The CPU lineup is a bit strange:

2011 iMac Comparison
iMac Model	$1199 21.5-inch	$1499 21.5-inch	$1699 27-inch	$1999 27-inch
Base CPU	Intel Core i5-2400S (2.5GHz quad-core)	Intel Core i5 2500S (2.7GHz quad-core)	Intel Core i5 2500S (2.7GHz quad-core)	Intel Core i5 2400 (3.1GHz quad-core)
CPU Upgrade Offered	None	Intel Core i7 2600S (2.8GHz quad-core)	None	Intel Core i7-2600 (3.4GHz quad-core)

The 21.5-inch iMac comes with a Core i5-2400S or 2500S by default. You can upgrade to the Core i7-2600S but only if you buy the $1499 system. Based on iFixit's teardown you should be able to do a CPU upgrade on your own since these are just standard socketed parts. Note that the 21.5-inch iMac only uses 65W TDP CPUs, the S suffix drops base clock speed a bit in exchange for lowering the max TDP from 95W down to 65W. Remember how turbo works, with lots of cores sharing a low TDP the base clock might be low but that means that you've got more room to turbo up when you start powering cores down. Despite the 2.5GHz base clock speed, the Core i5-2400S can turbo up to 3.3GHz with a single core active. The 2500S reaches a staggering 3.7GHz at max turbo.

The 27-inch iMac starts with a Core i7-2500S, but the upgraded model moves to a 95W Core i5-2400 clocked at 3.1GHz. Believe it or not but the i5-2400 can only turbo up to 3.4GHz. Running single threaded applications, the cheaper iMacs will actually be a little faster. There's also a Core i7 upgrade offered here, but again only for the more expensive iMac: Apple will sell you a Core i7-2600 for an additional $200.

Apple 2011 iMac CPU Comparison
	2.5GHz Core i5	2.7GHz Core i5	2.8GHz Core i7	3.1GHz Core i5	3.4GHz Core i7
Intel Model	Core i5-2400S	Core i5-2500S	Core i7-2600S	Core i5-2400	Core i7-2600
Base Clock Speed	2.5GHz	2.7GHz	2.8GHz	3.1GHz	3.4GHz
Max SC Turbo	3.3GHz	3.7GHz	3.8GHz	3.4GHz	3.8GHz
Max DC Turbo	3.2GHz	3.6GHz	3.7GHz	3.3GHz	3.7GHz
Max TC Turbo	2.8GHz	3.2GHz	3.3GHz	3.3GHz	3.6GHz
Max QC Turbo	2.6GHz	2.8GHz	2.9GHz	3.2GHz	3.5GHz
L3 Cache	6MB	6MB	8MB	6MB	8MB
Cores/Threads	4 / 4	4 / 4	4 / 8	4 / 4	4 / 8
AES-NI	Yes	Yes	Yes	Yes	Yes
VT-x	Yes	Yes	Yes	Yes	Yes
VT-d	Yes	Yes	Yes	Yes	Yes
TDP	65W	65W	65W	95W	95W

Now let's talk architecture. All of the Core i5s come with a 6MB L3 cache, while the upgraded i7s come with an 8MB L3. The even bigger difference? None of the Core i5s come with Hyper Threading enabled - they are four core, four thread chips. Only the upgraded Core i7s have HT enabled, giving them a total of eight threads. By comparison, all 15-inch MacBook Pros are mobile Core i7s with 8MB of L3 cache, four cores and eight threads. In other words, given the right workload, a high end 15-inch MacBook Pro could actually outrun one of these iMacs.

Hyper Threading only really matters with heavily threaded workloads (video encoding, offline 3D rendering) so I doubt most users would notice a difference, but it's still a shame that the iMac can't claim total superiority over the MacBook Pro.

I turned to MSR Tools once again to verify turbo operation. Running a single threaded instance of Cinebench the tools reported a maximum clock frequency of 3.3GHz. Assuming MSR Tools itself is keeping a second core awake, turboing up to 3.3GHz makes sense. I have no reason to believe that Apple is artificially limiting max turbo speeds, at least on the 27-inch 3.1GHz Core i5 model. Given how much room there is inside the iMac to dissipate heat, I don't see any reason for Apple to limit clock speeds here.

The quad-core CPU idles at 1.6GHz under OS X

Quick Sync is of course one of Sandy Bridge's biggest features and once again it goes relatively unused within the iMac. FaceTime HD supports it but iMovie, which ships with the system, has yet to be updated to take advantage of Quick Sync. If you want to upgrade to Sandy Bridge in order to get better video transcoding performance courtesy of its hardware decode/encode engines, I'd recommend waiting until Apple actually updates its software before making the move to Sandy Bridge on OS X.

Intel's Z68 Chipset, Thunderbolt & Display IO

Sandy Bridge integrates a GPU occupying roughly 20% of the quad-core CPU die. While what Intel calls its processor graphics is used on the MacBook Pro, outside of Quick Sync it's never used on the iMac. In fact, the processor graphics isn't even connected to the display at all.

Intel quad-core Sandy Bridge die

On the MacBook Pro Apple connects both GPUs to the display via a multiplexer and can instantaneously switch between which one is driving the panel without any frame buffer copying. With both GPUs connected and real time switching, accessing Quick Sync isn't an issue. On the iMac however, with only the discrete GPU connected, it is a problem. Apple claims this is why it used Intel's Z68 chipset: to access Quick Sync without a display output connected to the processor graphics. The Z68 based iMac actually went on sale before Intel's NDA on the Z68 chipset lifted. On the PC side we have Lucid's Virtu but for some reason Apple needs to use Z68 to achieve a similar end result. All other Z68 specific features go unused - there's no support for SSD caching and obviously no support for overclocking.

The other major change from the MacBook Pro is that the Thunderbolt controller no longer branches off of Sandy Bridge's on-die PCIe controller. Let's look at Intel's Z68 block diagram:

With Westmere (Clarkdale/Arrandale) Intel integrated a 16-lane PCIe 2.0 controller onto the processor die. The same controller made its way into Sandy Bridge. Traditionally these lanes are used for discrete graphics, the other major bandwidth hog within your system however the lanes are open to be used by PCIe device. In the 2011 MacBook Pro Apple used four of these lanes for Intel's Thunderbolt controller, leaving the discrete AMD GPU with a x8 interface. Even high end desktop GPUs aren't limited by a x8 PCIe 2.0 interface so there was no real performance penalty.

On the 2011 iMac however, Apple gives the discrete AMD GPU all sixteen lanes from the CPU. The Thunderbolt IC (which carries a different model number) branches off the Z68 chipset, which has 8 PCIe 2.0 lanes by itself.

Only four lanes are used by Intel's Thunderbolt controller, the remaining lanes are used for things like Bluetooth and WiFi. Do the math and you'll realize that four PCIe 2.0 lanes are only good for 20Gbps of bandwidth, plus DMI between the Z68 chipset and Sandy Bridge is limited to 20Gbps itself. A single Thunderbolt port is capable of 20Gbps of bandwidth (10Gbps in each direction), so that works out well (if you don't use any of the other PCIe devices in the system at the same time). While the 21.5-inch iMac has a single Thunderbolt port, the 27-inch model has two. That's a total of up to 40Gbps of bandwidth to Thunderbolt devices, but only 20Gbps to the controller itself. Don't be fooled by the presence of two Thunderbolt ports on the 27-inch iMac, you don't get any more bandwidth than you would on the 21.5-inch model - you can just hook up more displays.

Each Thunderbolt port on the iMac is good for at least one display output depending on what GPU you have driving it. The high end 27-inch iMac has two Thunderbolt ports, each of which is capable of driving two displays. Yes, you could theoretically have a 5-display setup driven off of a single iMac (given that even the upgraded iMac only has a 1GB frame buffer I wouldn't recommend doing such a thing).

The Thunderbolt ports aren't exclusively for video output, you can use one of the ports for video input. While you can use DisplayPort cables for video output, to make video input work you need to output video from a Thunderbolt port using a Thunderbolt cable. That means, at least today, the iMac can only accept video from a 2011 MacBook Pro (or technically another iMac) using a cable that doesn't yet exist on the market. You can expect to see Thunderbolt cables appear in stores very soon though.

Video aside, you will also be able to use the Thunderbolt ports for upcoming Thunderbolt devices as well. Each port supports a daisy chain for up to six Thunderbolt devices, meaning you can hook up a total of 12 devices to a 27-inch iMac.

The GPU

There are four discrete GPUs Apple offers in the new iMac and they're all from AMD, NVIDIA is completely out of the 2011 Apple lineup at this point. The entry level 21.5-inch iMac has the same Radeon HD 6750M as the upgraded 15-inch MacBook Pro. You can get a higher clocked 6770M in the upgraded 21.5 and base 27-inch models, and finally only the upgraded 27-inch iMac comes with a Radeon HD 6970M.

GPU Options
	AMD Radeon HD 6750M	AMD Radeon HD 6770M	AMD Radeon HD 6970M
Manufacturing Process	40nm	40nm	40nm
SPs	480	480	960
Texture Units	24	24	48
ROPs	8	8	32
Core Clock	650MHz	725MHz	680MHz
Memory Bus Width	128-bit	128-bit	256-bit
Memory Clock	900MHz	900MHz	900MHz
Frame Buffer	512MB GDDR5	512MB GDDR5	1024MB GDDR5

The 6970M doubles the number of shaders to 960 and doubles the memory bus width to 256-bits. The result is a GPU that has the fillrate and memory bandwidth to actually drive the 27-inch 2560 x 1440 panel...on sufficiently light games.

It's not all about compute and bandwidth, memory size matters as well. Unfortunately other than the upgraded 27-inch system, everything else only ships with a 512MB frame buffer. That's enough to drive the integrated panel but if you're running a high resolution external display as well you may notice some slowdown.

The upgraded 27-inch iMac can also be outfitted with an optional 2GB frame buffer for an extra $100. The added GB is nice but likely only useful if you have a specific application need or are running multiple displays.

2011 iMac GPU Comparison
iMac Model	$1199 21.5-inch	$1499 21.5-inch	$1699 27-inch	$1999 27-inch
Base GPU	AMD Radeon HD 6750M (512MB)	AMD Radeon HD 6770M (512MB)	AMD Radeon HD 6770M (512MB)	AMD Radeon HD 6970M (1GB)
GPU Upgrade Offered	None	None	None	AMD Radeon HD 6970M (2GB)

Apple sent us the upgraded 27-inch model because 1) I asked for it and 2) Apple thinks I really care about performance. Both are indeed true. The question I wanted to answer was whether or not the Radeon HD 6970M was going to be sufficient for panel-resolution (2560 x 1440) gaming on the 27-inch iMac both now and in the future. I don't have any older iMacs handy so unfortunately we'll have to do our GPU comparisons to the MacBook Pro line.

We'll start with Half Life 2 Episode 2. A game that's definitely long in the tooth but still represents a good workload for a Source engine game on Steam. It doesn't make sense running at resolutions below 1680 x 1050 on a 27-inch panel and thankfully the 6970M does a good job here:

While even the Radeon HD 6750M can manage a respectable 73.9 fps in our test, the 6970M offers nearly double that at 139 fps.

Half Life 2 Episode Two High Quality Settings
	2560 x 1440 - 4X AA/16X AF
27-inch iMac (Mid 2011) - AMD Radeon HD 6970M	112.8 fps

Running at native panel resolution, the 27-inch iMac is still very playable under Half Life 2.

Moving to a more modern Source engine game: Portal 2, shows that yes you still get playable frame rates at low and high resolutions although maxed out I could only manage 60 fps on the iMac. This is far superior to the 6750M which struggles at our highest quality settings, but at 60 fps there isn't much room to grow in game complexity before the 6970M begins showing its limits.

In fact we already see those limits with Starcraft 2:

Starcraft 2 - 2560 x 1440 - Ultra Quality Settings
	AT CPU Bench	AT GPU Bench
27-inch iMac (Mid 2011) - AMD Radeon HD 6970M	37 fps	51 fps

37 - 51 fps isn't the sort of buttery smoothness we've come to expect from a high end Sandy Bridge system running this game. It is very tough to drive the number of pixels we're talking about at native panel resolution. Thankfully for a game like Starcraft 2, as long as you're above 30 fps you're in good company. Drop the resolution to 1680 x 1050 and the 6970M looks a lot better:

I threw Windows 7 on the machine to put its GPU performance in perspective. Looking at Metro 2033 performance you get a good idea for where the 6970M falls compared to the performance mainstream to high end desktop GPUs we talk about regularly:

Overall performance is comparable to that of a GeForce GTX 460, which is still a great card - just not what we'd pick for driving a panel of this resolution. This is ultimately my issue with the GPU choices Apple offers with the new iMac: they are fast enough for most gaming on the Mac today, but likely aren't enough for panel resolution gaming for anything more strenuous (without dropping image quality). You can forget about most modern titles under Windows at panel resolution.

Funky Cables and SSDs

Apple doesn't just use the extra chassis volume in the iMac for heat dissipation, the system also comes equipped with a single 3.5" hard drive rather than the smaller 2.5" drives you find in notebooks. With the exception of the entry level iMac which comes with a 500GB drive, the remaining iMacs ship with a 1TB hard drive. By today's standards 1TB isn't anything to be excited about, particularly if you're storing a lot of music, photos and videos. The drives are all 7200RPM and come from either Seagate or Western Digital.

Retail drive cost is around $65 and the cost to Apple is likely even lower than that as an OEM ordering in bulk. With less than 3% of the cost of the high end 27-inch iMac being devoted to the hard drive it's clear that Apple doesn't view storage as anything other than a commodity. This philosophy extends to Apple's take on SSDs as well. While my review system didn't come with a SSD, Apple tells me that the 2011 iMacs use the same SSDs that the 2010 iMacs offered as an option (apparently a Toshiba based SSD - confirmed it's the same Toshiba SSD used in the 2011 MacBook Pro). The SSD isn't available on the $1199 iMac.

There's only one drive offered: a 256GB Apple branded drive for $500 in lieu of your internal hard drive. If you want it in addition to the 1TB hard drive it'll be $600 or $750 if paired with a 2TB hard drive. I don't have to tell you that while I believe an SSD is worth that much money, the drive Apple will sell you isn't exactly worth its upgrade cost.

While it's possible to add an SSD on your own, doing so requires a pretty lengthy teardown process. There are great tutorials online that help show you the way as well as provide you links to all additional cables that you'd need. There's no tray for the SSD to live in by default so you either have to cleverly adhere it to the inside of the chassis or order a part specifically designed to do so.

Apple opted for high quality fairly standard SATA cables for the iMac so I don't believe we'll see the compatibility issues on the iMac that we've seen in the MacBook Pro. In typical Apple fashion there are no spare power cables just laying around inside the iMac, instead you'll have to split power off from the hard drive to power both it and your aftermarket SSD. The whole process looks doable with a bit of patience and the right tools.

Apparently Apple likes to query HDD temperature quite frequently and uses that data in determining fan speed. In order to keep those requests off the SATA bus Apple supplies a custom power cable with surprisingly low gauge wires to not only power the hard drive but also return temperature data to Apple's fan controllers. The cable looks like this:

The standard SATA power cable is five pins. There's one pin for each voltage rail (3.3V, 5V and 12V) and two pins for ground. Apple's custom cable has seven pins, the remaining two are for temperature data. If you replace the iMac's internal hard drive with a drive that doesn't provide the appropriate temperature data, Apple's fan controller will go bonkers and try to cool what it assumes is an overheating drive.

When presented with this information, our own Brian Klug had a simple suggestion: short the two temperature pins to fool them into thinking all is good. It turns out that Apple provides a similar suggestion if you have a SSD-only iMac. Awesomely-named-site Hardmac.com has the scoop.

On the iMac, HDD power is provided through a proprietary connector on the motherboard. Short pins 2 and 7 (just connect the two using a simple wire) and you'll be able to run the iMac with no HDD plugged in and avoid the uber-spinning-fans. I'm guessing if you want to run with your own 3.5" drive in there that doesn't work with Apple's sensor setup simply short those two pins on the power cable itself (you'll have to tap into and modify the cable for this to work) and you should be good to go. Given that this is a review sample from Apple, and that Apple isn't too fond of me taking their review samples apart, I haven't tried the solution. But if shorting pins 2-7 on the motherboard header works, then shorting those two pins on the cable should work as well.

Now it's a pain that we even have to have this discussion, in fact it's the lack of easy upgrades that makes me so uncertain about the iMac. It's a fast machine with a great display but what happens in a couple of years when I need a faster GPU or even sooner when I want an SSD or larger HDD. At least the latter is possible.

With PCIe it's completely feasible to bring some modularity to these components. If anyone is willing to break the mold and explore something unique it's Apple, unfortunately I'm just not seeing that here.

FaceTime HD

Like the new MacBook Pros, the new iMac ships with a 1280 x 720 video/still camera mounted in the top bezel of the display. The FaceTime experience is pretty similar to what we saw on the MacBook Pro. The 720p video is encoded in real time (using Quick Sync) and sent at up to 2Mbps to its recipient. Image quality is pretty good assuming you have a well lit room and that you have the upload bandwidth to spare:

Photo Booth ships with the system and continues to capture at 640 x 480 by default. It's clear that Apple needs to do a better job of aligning updates to its software with its hardware release schedule.

Network Performance

Like the new 2011 MacBook Pros, the new iMac has an 802.11n WiFi adapter that supports up to three spatial streams. While Broadcom is responsible for the MacBook Pro hardware, Atheros provides WiFi in the iMac (at least for the 21.5-inch model).

As Brian correctly pointed out in our MacBook Pro review, Apple's Time Capsule and Airport Extreme have supported three spatial streams for a while - they just haven't had any clients that could use all three.

Each stream is good for up to 150Mbps, which brings the max negotiated speed of the new iMac up to 450Mbps:

In practice you get far less than that of course:

802.11n Network Performance Comparison
	27-inch iMac (Mid 2011)	15-inch MacBook Pro (Early 2011)
Peak Network Transfer Speed	150Mbps	133Mbps

Not as tuned for low power consumption the new iMac actually achieves higher throughput than the MacBook Pro connected to the same Apple Time Capsule.

Range is also improved compared to the MacBook Pro's 3x3 implementation. I saw more APs available on the iMac, which isn't too surprising:

The benefits of better range and higher throughput are less important on a desktop, unless you're one of those people who carries your iMac to coffee shops (in which case, yay?).

The Display

Apple offers two display options with the iMac: a 1920 x 1080 21.5-inch panel and a 2560 x 1440 27-inch panel. I tested the latter for this review.

Right away I noticed a huge difference in the default settings for the 27-inch iMac vs. my 27-inch Cinema Display. The new iMac has a lower white point, I measured 6102K uncalibrated vs. 7133K on the 27-inch Cinema Display. Here's a quick pic showing you the difference side-by-side:

27-inch iMac (left) vs. 27-inch Cinema Display (right)

Obviously that's just a calibration issue, but it shows a little more foresight on Apple's part with the 27-inch iMac. Viewing angles seem the same between the two as well. There is a noticeable change in how Apple maps brightness levels to the software OSD on the iMac vs. the Cinema Display however. The iMac's controls are far more linear:

I'm not sure if Apple has made similar changes in currently shipping versions of the 27-inch Cinema Display but it makes a whole lot more sense now. Linear controls for non-linear curves are silly.

The change in default white point alone should be an indication that Apple is experimenting with panels or panel vendors, the rest of the data seems to back this up as well. Maximum brightness is down a bit and but so are black levels, which means overall contrast ratio remains unchanged.

The new panel seems less uniform than the old one but it's not something that's noticeable in regular use, only if you actually measure the white/black levels on the panel.

Where the 2011 iMac does a lot better than my Cinema Display is in its color reproduction. The overall delta-E of the new panel is measurably lower than what was used in the first run of 27-inch Cinema Displays (and presumably last year's iMac):

I will say that despite what you see here numerically, you'd be hard pressed to tell a difference between the two panels as long as they're both calibrated.

Color gamut is a bit worse on the new panel vs. the old one from what I can tell. Both are WLED backlit which limits the spectrum of colors they can accurately reproduce.

Overall I'm just as much a fan of the 27-inch iMac display as I was of the 27-inch Cinema Display. The iMac is obviously bulkier but overall desk footprint is similar and you get a Sandy Bridge system as a part of the deal.

The Peripherals

I've never been a fan of wireless peripherals - I didn't want more things to charge. Last year I finally broke down and bought a wireless mouse: Microsoft's Wireless Mobile Mouse 4000. I didn't buy it for mobility, I just liked the form factor.

The iMac comes with all wireless peripherals. In fact, if you stick with WiFi for network access, there's only a single cable you need going to the iMac: power. By default you get Apple's Wireless Keyboard and a Magic Mouse.

The Wireless Keyboard is a Bluetooth keyboard that runs off of two AA batteries. It pairs effortlessly with the iMac and I didn't encounter any issues with interference in using it. The keyboard seems to burn through batteries quicker than the mouse, perhaps that's because I type far too much or there's an issue with power management under OS X. After a week of use I'm down to 81% on a fresh pair of batteries (this is my second set).

The keyboard itself is a lot like Apple's standard aluminum keyboard, just wireless and more compact. Apple chopped off the dedicated home/end key island as well as the numeric keypad. Under OS X Cmd + Left/Right Arrow take the place of Home/End for me so part of the sacrifice isn't a problem, but the missing numeric keypad is. I do entirely too much data entry (ahem, benchmarks) to not have a dedicated numeric keypad, and for some reason Apple doesn't offer the Wireless Keyboard with one.

If you don't type tons of numbers every day however, the Wireless Keyboard is really nice. Apple had to stick a function key to the left of the control key, which is a bit bothersome (leave my control/option/cmd row alone) but it's nothing you can't get used to. The footprint is great. I have a giant desk, but I always seem to run out of desk space. The Wireless Keyboard makes it so that I can reclaim a small amount of high value desk area.

Typing feel and keyboard angle are both great - no complaints there. I'm a fan of Apple's keyboards.

Pointing devices designed in Cupertino are another story entirely. I've never liked Apple's mice. It was a big enough problem that when I first tried my Month with a Mac experience I ditched Apple's mouse. There was no way I was going to give the platform a fair shake if I had to use that thing. Since then Apple has at least enabled double clicking - the surface of the Magic Mouse is touch sensitive, click with your right finger and you get a right click. The Magic Mouse has no scroll wheel but drag your finger around on its surface and you get the best scrolling experience on a physical mouse.

The Magic Mouse is also a Bluetooth device that quickly pairs with the iMac. I noticed under Windows there's always a second or two of lag before it recognizes the mouse whereas it's useable as soon as you can see it under OS X.

My complaints about the Magic Mouse are three-fold. As I've mentioned before, the Magic Mouse doesn't have soft rubber feet that glide around on your desk. Instead you get two hard plastic strips that just seem to scrape against all surfaces. Tracking isn't a problem, but it's not a pleasant experience.

The other issue I have is the form factor itself. Microsoft's Wireless Mobile Mouse 4000 is small but it has a nice curve to it that seems to match my hand very well. The Magic Mouse on the other hand doesn't conform to any part of my body. I can lay my hand flat on it but either I'm not conditioned to do that or that's not a very comfortable way to use the mouse for long periods of a time.

Finally there's the clicking noise it makes. Modern mice seem to have a solid but more muted click, whereas the sharp click of the Magic Mouse reminds me of the past decade of Apple mice. I assume that's what Apple was going for, but Apple's market share has grown considerably in the past 10 years - it's ok to let go of some traditions.

Apple does offer the Magic Trackpad as a no-cost option. I have a love/hate relationship with the Magic Trackpad as a pointing device. Scrolling and gestures are great on it, but I prefer a normal mouse for most everything else.

Power, Thermals and Noise

I started this review complaining about how loud the 15-inch MacBook Pro gets, but with 32x the physical volume the 27-inch iMac is near silent. Even under load the system is very quiet, almost too quiet. Apple chose a very lax fan profile which results in some very high external temperatures. The iMac takes in cool air from the bottom of the display and exhausts it up top behind the display. Playing Half Life 2 Episode Two I measured a maximum surface temperature of 125F at the exhaust vent. Again, unless you're doing something weird with the iMac on your lap this isn't an issue. Keep in mind that the Sandy Bridge CPU in the 15-inch MacBook Pro carries a 45W TDP and what's in the iMac is either 65W or 95W. Add in a larger, hotter hard drive and potentially a beefier GPU and you have a recipe for a pretty warm machine.

2011 iMac Power Usage
27-inch iMac (Mid 2011)	Idle	Cinebench R11.5	Half Life 2 Episode Two
Minimum Brightness	54.1W	108.3W	149.0W
50% Brightness	86.6W	141.6W	180.0W
100% Brightness	144.5W	198.3W	240.0W

With a large integrated display power consumption obviously varies depending on brightness. At idle, power consumption ranges from 54W to 144W. Under load the range quickly gets ever higher. I measured max system power consumption at 240W running Half Life 2 Episode Two.

Power consumption isn't out of control but you've got a billion transistor CPU, a 1.7B transistor GPU and a high resolution 27-inch display + backlight - it's going to draw some power.

Performance

Having never previously been a fan of the iMac, I don't actually have any historical performance data to compare to. What I do have however are scores from Mac Pros and of course the MacBook/MacBook Pro lines from the past couple of years.

Adobe Photoshop CS4 Performance

The Retouch Artists Speed Test we use for our CPU testing under Windows also works under OS X. We're running the exact same benchmark here, basically performing a bunch of image manipulations and filters and timing the entire process.

The high-end 27-inch iMac is a very capable Photoshop machine. A hair faster than the new MacBook Pro, the iMac delivers the same performance as an 8-core Mac Pro from 2009 or 2010.

Aperture 2 RAW Import

For my Aperture test I simply timed how long it took to import 203 12MP RAW images into the library.

We have a new winner here! The MacBook Pros were always limited by their slower 2.5" hard drive, but the iMac with Sandy Bridge in additional to a speedier disk give us better image import performance than the '09 and '10 Mac Pros. I told you this thing was fast.

Cinebench R10 & 11.5

I’m a fan of the Cinebench tests because they lets me show off both single and multithreaded performance in the same workload. First, the single threaded performance:

Sandy Bridge quad-core CPUs make no sacrifices. You get excellent single threaded performance which means general OS usage, launching applications and even rendering most web pages happens as fast as physically possible as the other cores are power gated and asleep. Start multitasking however and you'll see the Core i5 in this machine is no slouch:

There's still no replacement for more cores when it comes to heavily threaded applications, the past three years of 8-core Mac Pros are still faster than the new 27-inch iMac here. I suspect the upgraded Core i7 would at least let the iMac beat the 2008 Mac Pro thanks to Hyper Threading, but the other two systems are simply out of reach. For those users, you're better off waiting for the Sandy Bridge-E Mac Pro update expected sometime in Q4.

You'll notice in Cinebench R10 the 15-inch MacBook Pro is nipping at the heels of the new iMac. Chalk that up to the larger L3 cache and Hyper Threading, both advantages enjoyed by the MacBook Pro. Look at what those advantages do in Cinebench R11.5's multithreaded test:

Here the MacBook Pro actually gains on the iMac. More threads and more cache are better suited for the Cinebench workload. If you do a lot of offline 3D rendering and you want the iMac, I'd suggest upgrading to the Core i7-2600 that Apple offers. You get a not insignificant boost in clock speed but more importantly, Intel switches on Hyper Threading which gives you twice as many threads.

Quicktime H.264 Video Encoding

Our final benchmark is more consumer focused. Here I'm taking an XviD and converting it to an iPhone-supported H.264 format.

QuickTime doesn't make tremendous use of all cores all of the time, and thus the MacBook Pro loses its threading advantage. The iMac is our new champion of this test.

 

Final Words

The new 27-inch iMac repeats all of the things I liked about the new MacBook Pro. It's stylish and as always Apple was pretty smart about most of its component choices. Thanks to Intel's quad-core Sandy Bridge CPUs, the system is very fast. In fact, as many of our benchmarks have shown, if you purchased a Mac Pro in the past couple of years chances are the new 27-inch iMac is faster than it in most tasks.

It used to be that if you needed a fast desktop that ran OS X you pretty much had to shell out for a Mac Pro. With this generation I firmly believe that the 27-inch iMac is a real alternative. And unlike iMacs of the past, this new one is actually married to a display that the high end folks might actually want.

The display quality of the 27-inch iMac is excellent. Apple went with a different panel resulting in a better monitor than the standalone 27-inch Cinema Display we reviewed last year. Although this one comes with a computer attached to it, you still retain the relatively small footprint of the 27-inch display. I still believe that a 27-inch diagonal is the best overall balance of resolution and screen size available today if you need something beyond 1920 x 1200.

I'm not ridiculously pleased with the base configuration of the 27-inch iMac but I can't complain too much about 4GB of memory and a 1TB hard drive. I still would like to see an SSD standard, but even more I'd just like to see Apple make it easy to add an SSD of your own. As it stands you have to buy a pair of suction cups, pull off the magnetic glass cover, remove the LCD, remove the motherboard, add a new SATA cable and a Y-splitter for power and then find a place to stick your SSD in order to upgrade the iMac yourself. Or you could pay Apple $500 for a 256GB Toshiba based SSD.

It's really the upgradability that I'm most bothered by with the iMac, and it seems like such a solvable problem. Serial interfaces like PCI Express and SATA were designed to make routing simpler, so you could put peripherals in odd places and still get good performance. For years I'd seen manufacturers demonstrate concept designs for external GPU boxes but what I'd really like to see is a concept from Apple, I want to see the first modular all-in-one. Apple took a bold step pairing an expensive display with an all-in-one Mac, but I think it really does work. The CPU is clearly fast enough to last you a while, but it's the GPU that I'm most worried about. The upgraded Radeon HD 6970M is enough to drive the 2560 x 1440 display for games that are out on the Mac today, but what about in a year's time? Offering roughly the performance of a GeForce GTX 460 in games, the 6970M isn't enough to run even modern PC titles at panel resolution - and that's the upgraded GPU. There's clearly the room to dissipate heat on the inside of this machine, I'm not asking for more GPU power today, but just room to upgrade it down the line. Apple has done its best to provide you with a balanced system today, however I feel like the iMac may lose that balance over time as a result of its high resolution display coupled with a limiting GPU.

Putting my aluminum colored glasses on for a moment I do have to keep in mind that the iMac is still relatively cheap in the Apple world. Plus when you buy into a notebook and you need a faster GPU you just sell or give the old one away, display and all. Maybe I just feel different about it because the iMac comes with a much larger display and maybe I shouldn't. If we're ok recommending a $1799 MacBook Pro, then recommending a $1699 iMac with a similar shelf life shouldn't be any different.

I guess I still feel like there's room for innovation here and if anyone can do it, it's Apple. Apple did a great thing with the iMac - it proved that all-in-ones weren't dead and that they could be done well. History tells us that all-in-ones are dead ends because you can't upgrade them. Well, Apple built an iMac with a LGA-1155 socket and a GPU on a MXM module. Technically, if Apple wanted to support it, all the iMac would need is a firmware update to accept an Ivy Bridge next year since the CPU is both physically and electrically compatible with nearly all 6-series motherboards. Put that MXM module in a removable bay and now we're talking. I get that it's not really the Apple way to do any of this, but I feel like the potential is there. If Apple doesn't want to make a base Mac with the hardware of an iMac without the display that's fine, but perhaps give the enthusiasts a carrot to make the all-in-one experience a little more enticing?

Even taking into account my struggles with the upgrade cycle, I'd keep it and replace it with a Haswell iMac in 2013 just like I would do with a MacBook Pro. The net cost is roughly the same, I'm just not used to tossing out a display with each desktop upgrade. As I mentioned earlier, a lot of the value discussion here depends on what happens to displays over the coming years. If the roadmaps are more aggressive both for tablets and full blown computers, then upgrading to a new system with a new integrated display every couple of years isn't such a bad idea. But if the 27-inch iMac in 2013 - 2014 doesn't dramatically improve the quality of the display as it ramps up performance, it becomes a tougher upgrade to justify.

Having gone the mobile route and now using a MacBook Pro as my desktop, I'm very tempted by the iMac. It addresses all of the issues I have with the MacBook Pro, maintains most of the benefits but reintroduces the problem of portability. I started this article at my desk, but I just disconnected the MacBook Pro and moved my environment to the couch. No moving of files, no accessing network shares, I just physically moved my workspace. The appeal of mobility is tremendous, but it's not perfect. There is no replacement for tons of TDP, which is something only a desktop can provide. There's still no perfect solution, no one-size-fits all I'm afraid. As I mentioned earlier, when I'm traveling a lot and need to get work done - the MacBook Pro is a great solution. When I'm at home for an extended period of time? I'll probably miss the iMac to be honest. If you don't absolutely need the portability, then the iMac is a far better investment than a MacBook Pro in my mind. You get faster hardware and a nicer display for less money (at least comparing upgraded high-end models).

Maybe this is where tablets will eventually fit in. For the user who doesn't travel a ridiculous amount but still needs access, there's the tablet - but when he/she is at home, there's the iMac. Start traveling (or simply changing locations) more and the balance shifts towards more portable computing.

A lot of this discussion is a mind dump about trends in computing and ideas for the future, but if you're looking for a conclusion it's this: I like LG's 27-inch panel that Apple uses, I like Sandy Bridge and thus I like the 2011 iMac. If I lived a different life it'd probably be my desktop of choice, and that's something I never thought I'd say.