The 27-inch Apple iMac Review (2011)
by Anand Lal Shimpi on May 27, 2011 2:30 AM ESTIntel'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.
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KoolAidMan1 - Sunday, May 29, 2011 - link
iMacs don't use mobile CPUs. My gaming PC and my 2009 iMac have the exact same CPU, a Core i7-860boop - Saturday, May 28, 2011 - link
anand, i used to have the same dilemma you face regarding the syncing of files across multiple machines. i even did the same thing as you and tried to use an macbook pro as a desktop replacement. it didn't work out so well. a notebook that's powerful enough to be a desktop replacement isn't portable enough -- and a notebook that's particularly portable just isn't powerful enough to be a desktop replacement.The solution I found was to use google docs and other related online services to store all my work files. as you know you can access the files on any machine, and even be logged in on multiple machines simultaneously; documents can be shared with others for collaborative work; and it also solves the problem of data back ups and laptop theft since nothing is locally stored. my current Mac setup is a 13" macbook pro and the 2011 21.5" base model imac and with all my work stored in the cloud i've finally found an optimal solution to my workflow woes. hope this helps!
ananduser - Saturday, May 28, 2011 - link
Apple packages tech real well. Good display, reasonable PC, all'n'all a good looking AIO that especially does not compromise on the display side of things. Glad I am not in need for the OS or the hardware flexibility of the laptop combined with the mobility of the desktop.Even if Apple gets so much marketing coverage everywhere I am still glad that I see my own kind keeping criticism alive.
Hrel - Saturday, May 28, 2011 - link
That display is worth 400 bucks tops; it's insane to me that anyone would pay a grand for a display barely above 1080p. I can get a good ISP 27" 1080p display for 300, so that thing is worth 400 tops; which makes that whole system 300 dollars too expensive to even consider. Then there's all the laptop parts and non-upgradeability and Appleness to ruin the experience.Kristian Vättö - Saturday, May 28, 2011 - link
Find a similar display for 400$ then. It's ridiculous to argue that the display can't be worth more than 400$ when similar displays cost 1000$. If you don't think it is worth it, then that is your thing. It doesn't change the fact that the display is worth ~1000$.I also doubt that you can find a good 27" IPS display for less than 300$. Most of the good ones are either ~22" at that price range or you have to pay more.
donnyg - Saturday, May 28, 2011 - link
You can get a Hazro, which is literally the same panel as the current Apple CInema Displays minus the aluminum casing, for around $500 USD.Shipping will make it cost considerably more however.
KoolAidMan1 - Sunday, May 29, 2011 - link
There is a massive different in pixel density between a 27" display at 2560x1440 and 1920x1080, HUGE. Then there's the fact that your display is using a crap TN panel instead of an IPS, isn't LED backlit, etc etc.A good 24" IPS display from HP or Dell is going to cost $400-$500, and a 27" with the same panel from Dell or NEC is going to cost $1100-$1400.
For a site with a "techie" readership, it is amazing how little some people know about tech, or how much they are willing to excuse purely based on price. Yeah you can save money on a cheaper display, but it is going to be totally inferior in every way except for price. You get what you pay for.
MadMacMan - Saturday, May 28, 2011 - link
That's exactly right. DO YOUR RESEARCH, people. There is NO equivalent in the 27" category of HIGH-END displays and by that I mean not part but ALL of the following:LED back lighting (No CCFL bulb, thank you), in-plane switching (IPS); not your average (READ: average, as in mid-range, as in lame, as in cheap, as in what a lot of you might buy and post BS about how you're not getting ripped off by Apple because you're so much smarter; you know who you are). Finally, and perhaps even more problematic to find is its high RESOLUTION! 2560x1440. That's 78% more real estate than you get on a standard 1920x1080 display.
I dare anybody to Google me up a 26"-29" monitor with the aforementioned specs, but ALL of them, not one or two. Now go to Best Buy and buy yourself a cheap HP or order up an Acer and make sure you don't forget to rub it in. ;-)
donnyg - Saturday, May 28, 2011 - link
http://www.hazro.co.uk/HZ27WA.phphttp://www.hazro.co.uk/HZ27WC.php
IPS monitor: Check
2560x1440 resolution: Check
LED backlighting: Check
Price: 569 AUD for the the one with extra inputs/scalar,
Kristian Vättö - Sunday, May 29, 2011 - link
I don't know where you got your 500$ as 443£ is equal to 731$. That seems to be without shipping. Cheaper? Sure, but not that much.You can always save a few bucks if you do some shopping and build it yourself. The iMac, or any Apple product, has never tried to be the cheapest option or best bang per performance on the market. I would still say the new iMac is great value. I already mentioned why an OEM PC and a homebuilt one are not always comparable, especially when we get into an Average Joe level. Hardcore gamers will never be satisfied with Apple's offerings but to be honest, I don't get it why they complain then. Nobody is trying to sell them an iMac.