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
*When the MBA gets the HD3000 and Thunderbolt. We need an edit feature, lol.KoolAidMan1 - Friday, May 27, 2011 - link
The MBA should work once it gets a Thunderbolt port in the next revision. Current ones do not since they lack it. Also, the only MBPs that can drive the 2011 iMac are 2011 MBPs, nothing sooner without the Thunderbolt port.I am very curious to see if someone makes an adapter. I can't imagine that it would be cheap, but there would be at least some market for it.
damianrobertjones - Friday, May 27, 2011 - link
The hard drive cable/fan issue ALONE ensure that I'll never buy a machine like this. No. Freedom of choice and options is what I'd like and I'd prefer not to have to short any cables.TEAMSWITCHER - Friday, May 27, 2011 - link
Why does everyone want an iMac computer, just to crack it open and put a faster/larger/different hard drive in it. Why not just buy it and use it the way it is. That's what having a Mac is all about, buy it, use it, abuse it if you want to, but just enjoy it. I think that Freedom of choice work both ways.tipoo - Friday, May 27, 2011 - link
Well, what do you do when your out of warranty and the drive fails? Or you need a bigger one?TEAMSWITCHER - Friday, May 27, 2011 - link
I understand the concern, but a hard drive failure is actually a pretty rare event. I have had several Apple computers over the years, most of them notebooks, and never has a hard disk failed on me.That said, if your still worried about it you should buy the Apple care extended warranty for $169.00. That'll give you three years of warranty service.
mschira - Friday, May 27, 2011 - link
lovely machine I am almost ready to buy one, but:"you have to buy a pair of suction cups, pull off the magnetic glass cover, remove the LCD, remove the motherboard"
I don't know. I don't think I can swallow that....
so again no Mac for me...
M.
GeorgeH - Friday, May 27, 2011 - link
If the 27" model was upgradeable it would be my next computer - and the first Mac that I bought personally. Unfortunately the chances of Apple ever making upgradeable hardware are just about zero. If that SATA cable is any indication, their engineers are instead actively working to add BS complexity for no reason other than to keep Mac hardware "special".So instead of a Mac I'll just put together another ITX box and hope for the day that someone pairs a nice display with good design and upgradeable hardware.
alent1234 - Friday, May 27, 2011 - link
the resale values are so good that it doesn't make sense to upgrade them. and most people don't upgrade CPU and RAM that works on the same motherboard chipsets. they wait for a new generation of everything to buy something new.i did this years ago and got tired since the motherboards changed every few years anyway making me buy a new motherboard, CPU and RAM. might as well just buy a pre-built computer since it's about the same amount of money
GeorgeH - Friday, May 27, 2011 - link
I'd guess the best GPU in the 27" has about 6 months before I'd want to be upgrading it. I definitely would want a faster SSD than it comes with, and would probably want to upgrade that again in a year or so. The CPU could last me, but Ivy Bridge might be enough of a jump to make me throw some money away just because.Also, I actually enjoy tearing computers apart and messing with them as a hobby. Spending an afternoon every year or so ripping apart my hypothetical iMac would be fun for me - selling and buying a new one on the same schedule would be tedious.