Well, it’s happened again – Apple’s online store went down briefly this morning, meaning that the secretive company was stocking its virtual shelves with new product. As expected, when the curtain was pulled back, we all had new iMacs staring us right in the face, and they brought with them the customary slew of incremental upgrades over last year’s models. If you were paying attention when Apple refreshed the MacBook Pro earlier this year, a lot of this is going to be familiar to you.

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There were two major improvements in the MacBook Pros that made most of the headlines: an upgrade to Intel’s new Sandy Bridge processors, and the introduction of the new Thunderbolt port in place of the former Mini DisplayPort. Formerly code-named Light Peak, this Intel-developed port enables two-way 10Gbps transfer speeds between a variety of devices while also maintaining compatibility with existing Mini DisplayPort dongles and cables.

To see more about the particulars of Thunderbolt, you’ll definitely want to read the extensive write-up we did about the technology when it launched in the 2011 MacBook Pros – everything written there is true of the port in the new iMacs. You’ll definitely see Thunderbolt crop up in other Macs as the year goes on, and after Apple’s exclusivity agreement with Intel is up in 2012, you may start to see it pop up in PCs as well. Until then, use of the port in peripherals is and will probably continue to be rare, so the more immediate concern for us is the hardware upgrades in the new Macs.

2011 iMac Lineup
21.5-inch (low-end) 21.5-inch (high-end) 27-inch (low-end) 27-inch (high-end)
Dimensions (inches) 17.75 H x 20.8 W x 7.42 D 17.75 H x 20.8 W x 7.42 D 20.4 H x 25.6 W x 8.15 D 20.4 H x 25.6 W x 8.15 D
Weight 20.5 lbs (9.3 kg) 20.5 lbs (9.3 kg) 30.5 lbs (13.8 kg) 30.5 lbs (13.8 kg)
CPU 2.5 GHz quad-core Core i5 2.7 GHz quad-core Core i5 2.7 GHz quad-core Core i5 3.1 GHz quad-core Core i5
GPU AMD Radeon HD 6750M (512MB) AMD Radeon HD 6770M (512MB) AMD Radeon HD 6770M (512MB) AMD Radeon HD 6970M (1GB)
RAM 4GB 1333MHz DDR3 (16GB max) 4GB 1333MHz DDR3 (16GB max) 4GB 1333MHz DDR3 (16GB max) 4GB 1333MHz DDR3 (16GB max)
HDD 500GB 7200 RPM 1TB 7200 RPM 1TB 7200 RPM 1TB 7200 RPM
Display Resolution 1920×1080 1920×1080 2560×1440 2560×1440
Ports Gigabit LAN, Firewire 800, Thunderbolt, 4x USB 2.0, SDHC slot, separate audio in/out jacks Gigabit LAN, Firewire 800, Thunderbolt, 4x USB 2.0, SDHC slot, separate audio in/out jacks Gigabit LAN, Firewire 800, 2x Thunderbolt, 4x USB 2.0, SDHC slot, separate audio in/out jacks Gigabit LAN, Firewire 800, 2x Thunderbolt, 4x USB 2.0, SDHC slot, separate audio in/out jacks
Price $1,199 $1,499 $1,699 $1,999

All iMacs now come packing quad-core Sandy Bridge processors, dedicated graphics with 512MB or 1GB of memory (the high-end 27” model can also be configured with a 2GB 6970M), Thunderbolt (one port in the 21.5” model, two in the 27” model), and an HD Facetime camera (which supplants the previous generation’s iSight camera, making the white MacBook Apple’s last product to carry the iSight branding).

It’s too bad to see that all iMac models across the board still come with 4GB RAM installed by default, and Apple’s upgrade prices for memory remain ridiculous (bumping it up to 8GB across two 4GB DIMMS costs $200; market value for 8GB DDR3 kits is about $80). At least these iMacs continue to offer four RAM slots, versus the two slots on older iMacs – if 4GB is not a suitable amount for you, adding another 4-8 GB is easy and relatively inexpensive if you don’t pay Apple’s prices.

All of these internals are packed into a case that’s virtually identical to the aluminum unibody iMac design introduced in 2009, which itself was a gentle retooling of the aluminum iMac introduced in August of 2007. The point being, this refresh is all about the hardware inside: you’re not getting anything drastically thinner or lighter, and if you’ve seen an iMac in the last three or four years, you should have a pretty good idea of what you’re buying.

CPUs: The iMac Gets Sandy Bridged

Prior to the MacBook Pro refresh (and excluding the Mac Pro), the iMac was Apple’s only product line to transition completely away from Core 2 Duo processors to newer Nehalem-based Core i3, i5, and i7 processors – the white MacBook, the Mac Mini, and the MacBook Air lines continue to use the Core 2 Duo along with nVidia chipsets to save space and energy, and to get around using Intel’s previous-generation integrated graphics processor.

So the iMac wasn’t as far behind in CPU architecture as some of Apple’s other products, but the switch to quad-core processors across all models and price levels should give new customers a healthy speed bump over the previous generation. As we saw in our review of the Sandy Bridge MacBook Pros, Apple makes use of Intel’s Turbo Boost feature to make up for the quad core parts’ lower clock speeds relative to dual core parts in single-threaded applications.

The Sandy Bridge and Thunderbolt upgrades are more or less known quantities at this point – what impressed me most about the new iMacs was the GPU upgrade, especially in the entry-level iMac and the high-end iMac.

Graphics: A substantial bump

There are three new GPUs in the new iMacs: the AMD Radeon 6750M, 6770M, and 6970M. Unlike their desktop counterparts, the 6750M and 6770M are true 6000-series GPUs, and not just rebadges of the 5750 and 5770 (though, as always, making direct comparisons between desktop and mobile parts remains difficult).

On the entry-level iMac, the 256MB Mobility Radeon HD 4670 has been replaced by a 512MB Radeon HD 6750M – you get double the graphics memory, a switch from GDDR3 to GDDR5, DirectX 11, OpenGL 4.1, and OpenCL 1.1, as well as Eyefinity+ and UVD3 and the other Radeon 6000-series niceties. For gamers, this should substantially improve performance, especially if you’re interested in trying to game at the 21.5” iMac’s native 1920×1080 resolution.

Moving up the chain to higher-end models, the 512MB 6770M isn’t as big a step up from the previous generation’s 512MB Mobility Radeon 5670 – like the desktop cards, the 6770M is essentially a higher-clocked and gently tweaked revision of its previous-generation counterpart, and higher clocks are likewise all that separate it from the 6750M. You pick up UVD3, but a lot of the on-paper specs are the same. It’s still an improvement over the previous generation, but compared to the low end and (as we’ll see) the high end, it’s not as substantial.

And, finally, we’ve arrived at the high end 27” iMac, which gets a 1GB 6970M to replace last year’s 1GB Mobility Radeon 5750. The 5750 is more or less a midrange graphics part – the mobility 5600 and 5700 series GPUs all share the same core, codenamed Madison – but the 6970M is a true high-end part, complete with a 256-bit memory bus (compared to a 128-bit bus for the 5750) and more than double the shaders (960 in the 6970 versus 400 in the 5750). This, again, will drastically improve the new iMac’s utility as a gaming machine – the 6970M is much more capable of driving the 27” iMac’s 2560×1440 pixel display.

For the 27” models with two Thunderbolt ports, the 6000-series GPUs will also enable the use of three displays simultaneously, which will be handy for the Final Cut and Photoshop junkies who often invest in the higher-end iMacs.

Lion-Ready

The last thing I want to talk about is the subtle factor looming over these refreshed computers: Lion.

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OS X 10.7 is supposed to bring a lot of iOS features “back to the Mac” when it releases this summer, and since these Sandy Bridge Macs are going to be the first computers the new OS ships on, we’re seeing some preparation for it on the hardware end.

To drive the iOS inspired touch enabled features, each new iMac can come bundled with either the touch-enabled Magic Mouse or the Magic Trackpad at no extra cost (it’s your choice – the Magic Mouse is the default option). The vanilla Apple Mouse is still a selectable option, but will save you no money compared to its touch-enabled counterparts, which are more expensive at retail.

Apple is also beginning to push SSDs in its laptops to replicate the quick boot and shutdown times of iOS, and we’re beginning to see that in the new iMacs – while none of the computers include an SSD by default, you can configure all but the entry level to include a 256GB SSD as either the primary hard drive or a secondary drive. Characteristically, Apple hasn’t posted anything about the manufacturer of this drive or its controller – Apple uses Toshiba SSDs in the Sandy Bridge MacBook Pros, and recently switched to Samsung SSDs for the MacBook Airs, but there’s really no telling exactly what these iMacs are packing until it’s in your hands.

To replace the mechanical hard drive with a 256GB SSD costs a whopping $500 ($600 to get the SSD and keep the mechanical hard drive as well), though that’s not too far above the market price for an SSD at this capacity. Also note that, at this point, TRIM only seems to be enabled in OS X for SSDs direct from Apple – even if you can put in an SSD as an aftermarket upgrade, you may not be as satisfied with its performance. This may change in Lion, but we have no solid evidence to that effect.

Conclusions

With this refresh, Apple has done what Apple typically does: offer faster hardware in a similar physical package while maintaining price points across the board. Quad core processors and beefier dedicated GPUs make these better buys, relatively speaking, than last year’s models, but the iMac is still the iMac: a midrange-to-high-performance all-in-one with a high-quality display. Today’s upgrades do nothing to change the iMac lineup on a fundamental level.

That is to say, if you were in the market for an iMac already, congratulations! Today’s iMac is faster and more capable than yesterday’s iMac on all fronts. If an iMac isn’t what would best suit your purposes, though, today’s update won’t do much to change your mind unless you were looking for better gaming performance on the low and high ends.