The 27-inch Apple iMac Review (2011)
by Anand Lal Shimpi on May 27, 2011 2:30 AM ESTThe 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.
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tipoo - Friday, May 27, 2011 - link
Nevermind me, it was answered in the article.tipoo - Friday, May 27, 2011 - link
I heard that unlike previous iMacs, the new ones can only use another mac with Thunderbolt to use the iMac as a targeted display. Is that true? I wouldn't feel so bad about discarding such a system when the GPU and CPU feel too old in two or three years like Anand mentioned if I could use it as an external display, but I think the new ones are limited to only being used by other Macs. And that's also assuming Mac's in 3 years will use compatible Thunderbolt ports.TegiriNenashi - Friday, May 27, 2011 - link
What is wrong with this display? Just one number: 16:9.QuietOC - Friday, May 27, 2011 - link
I have used a 20" white iMac and 24" aluminum iMac. The later has a big persistent image problem. Evidently IPS pixels don't work well in a hot environment. The low noise level of the iMac is nice to mostly not hear, but the visual noise might be worse.Also the cheap 320GB WD Caviar failed by randomly disappearing which may have be heat related, and the USB ports have also started randomly disconnecting. The mouse and keyboard just stop working during the day and I have to unplug them and plug them back in. So, no, I would not recommend getting a $1000 monitor with a computer mounted inside it.
KoolAidMan1 - Friday, May 27, 2011 - link
I've owned both the 24" iMac you talk about and a 27" from late 2009. Image persistence became a problem with the 24" models, as well as the CCFL losing some of its brightness by the two year mark.The new 27" models do not have either issue. Image persistence has been fixed, and I don't expect there to be any fading since LED backlights don't suffer from the same degredation issues that CCFL backlit displays do over time. On a related note, I have a NEC 2490WUXi as my secondary display. That monitor uses the same 24" H-IPS panel that the old 24" iMac did. It has minor image retention issues, but not to the same degree as the iMac had. Whatever LG did with their new 27" panels seems to have addressed that problem.
zhill - Friday, May 27, 2011 - link
First off, nice article Anand. Well presented and I think your perspective is a common one in this case. I agree that the lack of upgrade options and rather mediocre gpu performance are certainly off-putting for a machine in this price range, but I also think that your observation that if you are willing to spend $1800 for a laptop with a reasonably short lifecycle then the iMac is not much different. I think you've really hit the point there--the iMac's target customer.I would argue that most iMac users are not highly technical, power users. They are people that want a big screen and don't need the portability of a laptop. These people, like my parents, value the simplicity and ease of use of the iMac and the fact that their workspace is often small and would rather it not be covered in cords and cables. In that case not only does the iMac make sense but it's lifespan is substantially longer and all the GPU they need is enough to drive the system and maybe do some video editing. Gaming prowess has never been an apple concern and I doubt it will be until Steve Jobs decides to buy Activision or EA. I do like the iMac from a compute appliance perspective, just plug it in and compute--no fuss. Also, trying to make a reasonable gaming rig with a 2560x1440 display is a fairly daunting task even with today's cards. You would have to be near the top-end and that's a whole lot of power and heat to dissipate in a reasonably small enclosure (considering the size of a 6970 or 580 card by itself).
I also have to say that Intel's recent willingness to keep switching chip sockets has made upgrades far more painful than they should be (yes, I have a core i7-920 with socket 1366 that is now essentially orphaned).
Alberts - Friday, May 27, 2011 - link
Securedoc for Mac from a company called Winmagic supports SSD's with encryption hardware as long they adhire to the opal specification from the trusted computing groupJimmiG - Friday, May 27, 2011 - link
You can't upgrade the hardware and you can't separate the computer from the display so you can keep using the display long after the hardware has become obsolete.That's pretty much the oposite of "green".
Spazweasel - Friday, May 27, 2011 - link
This may be old news (I'm not going to wade through 6 pages of Apple-hating trolls to see), but you CAN use your 27" iMac as a monitor:http://support.apple.com/kb/HT3924
It's called "Target Display Mode".
KoolAidMan1 - Friday, May 27, 2011 - link
Note that it is only talking about the 2009 and 2010 models with mini-DP ports. Those can take an external source so you can use the 27" iMac as a monitor. I use it every day as the primary monitor for my gaming PC.The new 2011 iMacs have different requirements since they switched to Thunderbolt ports. Until an adapter or something comes out, the only sources that can output a video signal to the 2011 iMacs are Thunderbolt equipped computers. For the time being this only limits them to 2011 Macbook Pros and other iMacs (which would be a weird application).
I love the iMacs, but as someone who uses Target Display Mode every day, the new requirements bother me. It won't be a problem in a year or so when Thunderbolt becomes more common, but for the time being it is pretty limiting.