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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iwod - Friday, May 27, 2011 - link
My problem is with Apple's Memory upgrade. They have 2x 2GB fitted which means if you want 8GB you either have to pay sily amount to apple, or buy 4GB x2 yourself and sell your original to someone else.As soon as the hardware encoder inside Intel can be accessed through Mac OSX, i believe 4 Core 8 thread will be enough for 99.9% of my task. Next year iMac GPU upgrade should be much more important then CPU IvyBridge.
And only if Apple actually make Z68 Intel SRT to work. We need SSD, in cache or main drive.
setzer - Friday, May 27, 2011 - link
Actually these iMacs have 4 so-dimm slots, so you should be able to get 8gb's fairly easily and cheap, though if I was changing the memory I would also change the hdd in one go, opening that can is hard work..FATCamaro - Friday, May 27, 2011 - link
Yeah I bought the 27" with the SSD upgrade and bought memory separately. SSD isn't that much more than retail and the imac is a pain to open. The memory is a bit of a ripoff though.Zandros - Friday, May 27, 2011 - link
Isn't the memory accessible through removing a single screw at the bottom of the iMac, though? No need to go in through the display just for that.archer75 - Friday, May 27, 2011 - link
Actually it's 3 screws ;)But there are 4 ram slots. I just bought 16gb from newegg and plugged it in. Cost less than what apple would charge for 8gb.
KoolAidMan1 - Friday, May 27, 2011 - link
Anand - First off, great review as always.The conclusions you reached regarding the iMac's performance "finally" getting to an acceptable point is something that I came to with the release of the mid-2007 24" iMacs. Prior to that I had a PowerMac workstation for Final Cut Studio. The Core 2 Duo used in the 2007 iMac convinced me that an all-in-one would finally be a suitable replacement instead of a Mac Pro, and it was. It cost me much less than a Mac Pro while still giving me good performance and it had a 24" IPS display built in, which at the time ran $1000 by itself from NEC or Apple.
The 27" iMac released in late 2009 was a similar deal: a powerful i7-860 machine combined with a $1000 27" IPS display. iMacs make upgrading simple too, you just pack the whole thing in the original box and ship it off. The only thing you have to mental your way past is letting go of the display, and that isn't hard for me based on the fact that the 27" display in the current iMac is spectacular. It was a more than worthwhile upgrade from my prior 24" iMac, and it didn't cost me too much given that I sold the old one for about 60% of what I paid.
The 27" iMac display also functions as the primary display for my gaming PC. Unlike the iMac, my PC has SLI video cards so it can tear through that 2560x1440 res with no problem. Unlike the iMac, my PC isn't for work, it is for play. :)
This brings about my main issue with the 2011 iMacs, and it isn't something that was addressed in this review. I'm talking about the new requirements for Target Display Mode (using the iMac as a monitor for an external source) now that the mini-DP port was replaced with a Thunderbolt port. The only sources that you can use on the new iMacs are those equipped with Thunderbolt ports. For the time being this limits you to 2011 Macs, that's it. No old Macs, and no PCs until next year at the soonest.
Coming from someone that uses an iMac as an external display every day, that is pretty disappointing. Perhaps an active adapter or something will come out, but for the time being it really limits that aspect of the new iMacs.
Thanks again!
KoolAidMan1 - Friday, May 27, 2011 - link
Sidetrack - I suggest testing Starcraft 2 with ultra textures and medium settings. My PC has plenty of juice to run with everything cranked, but unless you take a still frame and examine it, the difference in visual quality between medium and ultra settings is not noticeable. The difference in framerate is VERY noticeable though, which is why I run at medium settings with ultra textures. Nice and fast while still looking pretty.I'm very curious to see how the new iMacs would run with those settings. In my own experience you're looking at nearly a doubling in framerate, but that is also with an SLI setup that may not have the same performance delta as the single GPU in the iMac. I also saw a huge difference with my laptop, but I didn't examine the framerate as closely with it so I can't say for sure if it is "nearly double" in that case.
jonwd7 - Friday, May 27, 2011 - link
The price comparison chart on the first page is wrong. I haven't made it through your review far enough to tell, but either you did not receive the high-end iMac, and you're quoting the wrong price ($1999) for the stats you've listed, or you did receive the high-end iMac, the price is right, but the stats are wrong.The stats you have listed are for the $1699 model.
krazyderek - Friday, May 27, 2011 - link
i noticed this as well, specifically this means,the $1999 model currently features the 6970 1gb, and 3.1ghz quad core i5
the $1699 model currently features the 6770 512mb not the 5xxx
in fairness the $1499 model should really be used along with the $1199 to compare to those other price points.
The $1999 model is in a completely different class and should be compared to it's appropriate competitors
psonice - Friday, May 27, 2011 - link
I'd say this isn't really much of an issue. When most people upgrade, they sell their old box - and the mac holds its value incredibly well. So what actually happens is in a couple of years you sell the old box for a large chunk of cash, and spend a smaller-than-expected sum on the new one.Basically, macs are surprisingly cheap when you factor in the resale value. You either keep them long term (and they pay for themselves then anyway), or you sell after a few years and get half your money back. This is assuming it doesn't break down - if that happens, they're very expensive ;)
Example: My 2007 24" imac was ~£1200. Resale value for similar spec on ebay today: ~£650-700. That means it's cost me around £500-£550 over 4 years, roughly the cost of a low-end desktop with an OK screen.
Oh, and I did upgrade mine to SSD (I've ignored that when looking at the prices). Yeah, it's a "fun" upgrade, and I ditched the HDD completely so I missed out on the 'removing the motherboard' stuff. Suction cups aren't actually required - you can get by with a pair of car windscreen mounts for GPS.
An easier way to access the HDD would be very welcome - especially as the new ones come with a special SATA connector so you'd need to buy an apple-specific drive too! (Not sure if this was covered in the article, I skipped a lot of it, but it's a pretty major downside for us technical types - the average punter probably wouldn't care less).