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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KoolAidMan1 - Friday, May 27, 2011 - link
"The example given by headbox is a prime example."I can't think of any Mac user who would really try this. I mean, I plug my gaming PC into my 27" iMac as a primary display through the mini-DP port, and I figure I'm in an extreme minority of users. People who plug consoles and BR players and who would need a converter box is be an even tinier number of users.
Don't get me wrong, I'm annoyed that the 2011 iMac has new Target Display Mode requirements, but the limitations of prior models in terms of using set-top boxes (consoles, Blu Ray players) isn't statistically a big enough number to get bent out of shape over, IMHO.
Tros - Friday, May 27, 2011 - link
"How are you going to upgrade the motherboard on a proprietary and overpriced all in one?"This is as much of a criticism on laptops, tablets, smartphones, as all-in-one units. And guess what: That proprietary junk has been of great value to a lot of people, especially if it has an aesthetic appeal.
Penti - Friday, May 27, 2011 - link
While certainly great for what they for probably, it's definitively not the same thing using 23" 1920x1080 120Hz TN-screens with Nvidia 3D Vision as with a good IPS or PVA screen with proper viewing angles and for mostly other uses then gaming. Of course you need your PC to your triple display gaming machine and a strong GPU too.rubaiyat - Wednesday, September 7, 2011 - link
Do you actually use your computer for much besides gaming?I'd rather have an excellent monitor than some dodgy and essentially useless 3D 'feature'.
But that separates consumers in all areas. Those who will see a movie because it has (very loud) surround sound and pseudo 3D with lots of explosions, and those who will see a movie because it actually IS a good movie.
My iMac27 has a brilliantly sharp and accurate 27" 2540x1920 display, that thankfully is not 3D nor runs generally awful Windows grade video.
nafhan - Friday, May 27, 2011 - link
I'm fine spending more on a monitor than a desktop... However, I'll usually go through two or three desktop hardware upgrades before I replace my monitor.fitten - Friday, May 27, 2011 - link
And when the monitor is the majority of the cost of the system, it makes sense to reuse it for future upgrades. Monitor technology seems to evolve slower than the rest of the system so barring some major changes, keeping it for several upgrades won't 'set you behind' any. So, reusing a monitor is an extremely cost efficient technique to keep your computer 'modern'.Spivonious - Friday, May 27, 2011 - link
Exactly. I've had the same NEC (Mitsubishi tube) CRT on my desk for 15 years. The picture is still fantastic and blows any TN-panel LCD out of the water.KoolAidMan1 - Friday, May 27, 2011 - link
Good thing they use the best IPS panels in these things. :)Guspaz - Friday, May 27, 2011 - link
Colour-reproduction wise, perhaps, although that depends on the backlight. In terms of detail and a crisp image, even a cheap TN panel will destroy an old CRT, and IPS panels will match or surpass such a CRT.I'm reminded of a friend of mine, who for years (until perhaps 2-3 years ago) insisted that his old CRT monitor was fine, despite the fact that it was so out of focus that 14 point text was unreadable. He finally relented and upgraded when we proved to him that he was in denial when we realize that the reason he didn't have trouble reading on the monitor was because he increased the text size by 200-300% when he used the monitor. Now, I'm not suggesting that your monitor is out of focus, a good CRT monitor can have excellent sharp detail. But even the best of them comes nowhere close to a half decent LCD.
KoolAidMan1 - Friday, May 27, 2011 - link
Not at all. Sell the iMac and get a better monitor that comes in the next update, it happens every 2-3 years. Resale value is also high.