Apple's new 2011 iMac range retains the form factor of the 2010 models, but enjoys a very significant component upgrade. Second-generation quad core Intel Core i5 processors are used throughout the 2011 iMac lineup - which includes two 21.5-inch models and two 27-inch models - where previously all but the most expensive model had dual Core i3s.
New graphics give up to three times the power of the mid-2010 iMacs, and the Thunderbolt port could revolutionise I/O technology.
The 2011 21.5-inch iMac reviewed here is the new range's entry-level model, costing �999. It offers a quad core Intel 2.5GHz Core i5 processor, a great leap forward from the dual core 3.06GHz Core i3 used in the cheapest 2010 release.
Its discrete graphics chip is a powerful AMD Radeon HD 6750M, with 512MB of GDDR5 memory, up from an ATI Radeon HD 4670 with 256MB of GDDR3 RAM.
The Mini DisplayPort has been replaced by a Thunderbolt port, Intel's exciting new I/O technology that can support up to six daisy-chained peripherals and data transfer speeds of up to 10Gbps in both directions. It's over 20 times faster than USB 2.0 and 12 times quicker than FireWire 800.
Thunderbolt also supports video, and can be used to connect an external monitor. It can even function as a video-in port, allowing you to use the iMac's gorgeous 1920x1080 pixel 21.5-inch LED-backlit glossy widescreen display as a screen for another device. The SD card reader is retained, but it now accepts SDXC cards for a theoretical maximum capacity of 2TB, with cards of up to 64GB already available.
For those who like video chat, the built-in webcam has been upgraded to a FaceTime HD camera, giving 720p resolution, a 16:9 aspect ratio and a much-improved low-light performance. Yet despite these improvements, the entire range is now cheaper than before. Not hugely so, but this particular model is �21 cheaper than its predecessor.
The 2011 refresh sees the entire Apple iMac range, including this 21.5-inch model, move over to Sandy Bridge processors, Intel's second generation of Core-i chips.
Based on Intel's 32-nanometer process technology, Sandy Bridge chips combine the processor, cache, memory controller and graphics engine on a single chip. This means data doesn't have to travel as far, making for increased performance and efficiency.
Sandy Bridge takes a new look at the Core-i chips' Turbo Boost technology. Turbo Boost 2.0 shifts core frequency in smaller increments than before, allowing the processor to better manage its performance without sacrificing efficiency.
Turbo Boost automatically shifts or reallocates CPU cores and processor graphics resources, tailoring a workload to the task in hand and giving immediate short-term performance acceleration when needed, by allowing the CPU to operate above its stated speed.
Unfortunately the Sandy Bridge processor used in the off-the-shelf iMac range lacks a Hyper Threading feature, which would've let each of the processor's cores run two threads at once.
All four standard 2011 iMac models use quad core Intel Core i5 processors, with a Core i7 (which does Hyper Thread) available as an Apple online store custom option for the more expensive release in each of the two sizes. The entry-level 21.5-inch 2011 iMac reviewed here has no processor upgrade option.
The new iMacs use AMD Radeon discrete GPUs throughout, for up to three times the performance offered by the previous generation. This entry-level 2011 iMac uses an AMD Radeon HD 6750M graphics processor, with 512MB of on-board GDDR5 memory.
All the new 2011 iMacs have Thunderbolt ports, with the two 21.5-inch models (including this one) supporting a single port, and the 27-inch iMacs having two.
Unlike the previous generation, where only the larger all-in-ones could be used as a display for another video-out device, all iMacs in the 2011 range offer a Target Screen Mode, allowing you to connect a compatible product to the Thunderbolt port and use the iMac as a display.
At the moment, this feature requires a Thunderbolt-to-Thunderbolt connection, so it can only be used with one of the new 2011 MacBook Pros (at least until the next generation of Mac minis are released). However, we're assured that third-party manufacturers will be able to make adapters for other video-out protocols such as Mini DisplayPort and HDMI.
Maybe one day we'll be able to use our iMacs as screens for our PS3s, Xbox 360s and Blu-ray players.
The new FaceTime HD camera on the 21.5-inch 2011 iMac gives 720p resolution and a 16:9 aspect ratio. You can only use FaceTime in HD when you're chatting with another device that has an HD camera. You can still call people using older FaceTime cameras, such as those with older iMacs, but only at standard 640x480 definition.
The new camera has a much better low-light performance than the one it replaces on the 2010 iMacs, and because it uses the Sandy Bridge-integrated video encoder, it doesn't tax the CPU.
The 2011 21.5-inch iMac put in a stellar performance in our benchmarking tests, proving way ahead of the cheapest 2010 iMac, and even outperforming the last generation's top-of-the-range model in several key areas.
In our Xbench test, where we look at the CPU, memory and hard drive performance, it scored a comfortable, if unremarkable, 15.7% increase over its predecessor.
But its quad core processor really paid dividends in our Cinebench 3D rendering test.
Restricting the processor to only a single core, it was 18.8% behind the older model, as its 2.5GHz CPU was outpaced by the 2010 iMac's 3.06GHz chip. But with all cores in play, its quad core Intel Core i5 soundly beat the last-generation iMac's dual core Intel Core i3, recording an increase of over 56%.
Interestingly, in this multiple-core Cinebench test, this entry-level 2011 iMac also beat the most expensive off-the-shelf model in the 2010 iMac range ? the �2,249 27-inch SSD performing just under 7% faster.
It's a similar story with our movie encoding test, where we time how long it takes QuickTime 7 Pro to encode a five minute, 720x480 sample video. The 2011 21.5-inch iMac did it in just 128 seconds ? more than a minute faster than its predecessor.
The top-of-the-range mid-2010 iMac 27-inch SSD we tested last year, a 2.8GHz quad Core i5 with a solid-state drive added as a custom option, only managed 131 seconds.
In our gaming test, the 2011 21.5-inch iMac handled Doom 3 at 169.7 fps ? 28.4% faster than the equivalent 2010 model, but not as fast as the previous generation top iMac's 178 fps.
We won't see the best of the Thunderbolt port until a significant quantity of peripherals are released, although a Mini DisplayPort display can be plugged directly into the Thunderbolt port. DisplayPort, DVI, HDMI or VGA displays are also compatible, using existing Mini DisplayPort adapters.
And remember, although capable of 10Gbps, the Thunderbolt port might not be the limiting factor for data transfer speeds. To get the most from Thunderbolt, it's best to use a RAID drive, streaming data from more than one HDD. But even a single external hard drive that can only manage maximum speeds of 3Gbps will prove almost four times as fast as a FireWire 800 connection.
Our iTunes encoding test produced disappointing, if entirely predictable, results. This 21.5-inch iMac encoded our test CD in six minutes and 13 seconds, an almost identical speed to all recent Macs other than the Mac Pro.
This is because the optical drive is proving the limiting factor. It really is time Apple gave us something faster than the current 8x SuperDrive. We're never going to get a Blu-ray drive due to Steve Jobs' much-publicised dislike of the format's licensing terms, but a faster DVD drive is long overdue.
Our only other complaint is the lack of custom options for those who order through the Apple online store. There's no way of improving the processor, the 21.5-inch is the only iMac in the current range that doesn't give you a solid state drive option and you can't even pick a higher-capacity hard drive.
Unlike the MacBook Pros, there's no matte screen option for those who dislike glossy displays.
Memory can only be boosted to 8GB, despite this iMac being quite capable of supporting 16GB as offered with the rest of the range. However, it's best not to buy extra memory from Apple anyway. It's easy to fit it yourself, and buying from third-party vendors is much cheaper.
On a positive note, all iMacs in the current range now let you dispense with the Magic Mouse in favour of a Magic Trackpad, if you wish.
The 2011 refresh represents a great leap forwards for the iMac range. Although the enclosure is unchanged (apart from the ports at the rear), the switch to new second-generation Sandy Bridge processors and powerful AMD graphics give the new 21.5-inch iMac a massive performance boost over the previous generation.
We liked
The entry-level 21.5-inch 2011 iMac's quad core 2.5GHz Intel Core i5 processor's Sandy Bridge architecture combines the processor, cache, memory controller and graphics engine on a single chip for improved efficiency.
Its Turbo Boost 2.0 function is also an improvement over that offered by the first generation of Core-i processors. When more processing power is needed, Turbo Boost takes the processor over its quoted clock speed for short periods. Turbo Boost 2.0 activates more often and keeps the processor working at higher speeds for longer.
In our benchmarking tests, the 21.5-inch 2011 iMac performed extremely well, belying its position as the entry-level model. In fact, in several significant tests, it outperformed the high-end model from the 2010 range ? an incredible achievement considering less than a year has passed between updates.
The screen is gorgeous, with bright, vivid colours and excellent viewing angles, and the new Thunderbolt port will prove very useful over time, as compatible peripherals and adapters are released.
The SD card reader now supports higher-capacity SDXC cards, and the built-in camera has been improved, giving HD resolution, a 16:9 aspect ratio and better low-light performance.
We disliked
There's little to complain about here. The configuration options available to those who order from the Apple online store are disappointing.
There's no SSD option, no means of increasing your hard drive capacity and memory upgrades are limited to 8GB, even though this 21.5-inch iMac is quite capable of supporting 16GB.
The optical drive is slow too, and for all its strengths, the processor lacks the Hyper Threading feature offered by many Sandy Bridge processors.
Verdict
Even at just under �1,000, this 2011 entry-level 21.5-inch iMac is excellent value for money (and �21 cheaper than the previous generation's cheapest model).
A massive performance boost means it actually rivals the power offered by the high-end 2010 iMac 27-inch SSD from the previous generation, and its new Thunderbolt port will prove its worth over time.
It could use more configuration options, and the whole of the new iMac range would benefit from a faster optical drive and a matte screen option, but overall, it's a superb update to an already-popular machine.
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