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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Spazweasel - Friday, May 27, 2011 - link
Thanks for the clarification.Spazweasel - Friday, May 27, 2011 - link
So here's a question. While the display is in Targeted Display Mode, can the computer itself be active? It would be nice to be able to have the computer available for computation tasks, acting as a server, etc. on its own while the display was being used by an external device. I wouldn't expect it to be so, but perhaps you as someone with first-hand knowledge would know if it's possible.Thanks!
KoolAidMan1 - Friday, May 27, 2011 - link
Yes, the computer portion of the iMac can still be cranking away when the video signal is switched to another source. I've had it encoding video as I play Starcraft 2 or whatever on my PC, using the iMac as its display.It is pretty nice.
archer75 - Friday, May 27, 2011 - link
So I bought one of these imacs right at launch. Upgraded the processor to the 3.4ghz i7 and got the 6970m 2gb. Later got 16gb of ram on sale at newegg.In terms of gaming I only play at native resolution 2560x1440 and must say this imac does slightly better than my i7 920, 460GTX 768mb PC does at 1920x1200.
Crysis 2 on medium settings gives me frame rates in the 30-50 range which is perfectly fine for me. Medium doesn't look any different than high to me so i'm happy with that. Very smooth gameplay with Bad Company 2 and Portal 2. WoW on ultra settings is flawless. Civ5 plays well. Age of Conan at max is pretty smooth, not perfect but certainly better than my gaming PC. EQ2 runs very well at one step down from their super high ultra setting or whatever they call it. Running max settings with Dragon Age.
I have 7 other PC's in the house, 4 running Win7, 1 running WHS 2011 and the 2 others running XP. I built most of them. And I had debated building another gaming system or getting the imac and decided to mix things up a bit and must say I really do like the imac.
Bob Forsberg - Friday, May 27, 2011 - link
Just about ready to purchase a new 27" iMac to replace my white 24" 2.16GHz iMac from 4 years ago.You made choices easy on processor types as well as providing answers to many of my questions. Thanks for the thorough analysis of this great machine.
CharonPDX - Friday, May 27, 2011 - link
"I've always kept displays through several upgrades, but you can't really do that with an iMac."One thing Apple has implemented on their 27" iMacs since they added Mini DisplayPort is that you can use the iMac as a DisplayPort monitor.
So when this iMac gets replaced, you can continue to use it as a 27" display on another computer with DisplayPort video. Be that another iMac (and have two displays), a Mac Pro, a Mac mini, or even a PC with DisplayPort (as most Dells have now.)
I know a customer that has two last-gen iMacs side-by-side: One as his workstation and one as a secondary display and VM host. He interacts with the VMs remotely from the 'workstation' machine, and has two 27" high-res displays on his primary system. If he ever really needs to interact locally with the VM machine, he just plugs a keyboard and mouse directly (although he generally VNCs over.)
tipoo - Friday, May 27, 2011 - link
Actually these new ones will only work with Thunderbolt, not DP unfortunately. So for now, just the Macbook Pro's can use it. The last gen could work with any displayport connection so its a step back IMO.tipoo - Friday, May 27, 2011 - link
I'd really like a decibel reading for a few computers in future reviews. ie, you say the MBP is loud, but how loud? I'd like to see it compared to other popular laptops at idle and under load.Hubb1e - Friday, May 27, 2011 - link
To understand an iMac usage model, you have to get over your idea that you upgrade your PC components. When you outgrow the GPU, you simply upgrade the whole Mac and sell the old one on the used market. The used market for these things is huge so you really aren't dropping much cash by ditching the old model for a new one. You aren't really ditching the monitor, you're simply making an upgrade for the GPU and a new screen comes with the upgrade. It's typically a sideways move in screen quality and you aren't losing any real value there by replacing it. You might drop $600 (accounting for taxes) when you drop the iMac after 1.5 years, but you get $400 worth of GPU and CPU upgrades. So, you do pay a bit for the Mac experience, but I think you can still keep the upgrade path going with a Mac.Keep the box and it's super simple to unload a used Mac.
dingetje - Saturday, May 28, 2011 - link
is there any chance of a review of some 16:10 screens? for instance ASUS PA246Q