Thunderbolt iMac: The perfect compromise

Apple's blazing-fast, elegant, and economical everything-in-one goes where ordinary desktops can't

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Pundits have predicted the death of the desktop for years. I wish it could be so. No technology is more deserving of retirement than the sheet-metal black box and tangle of cables that is the standard PC.

Notebooks and tablets have undeniable appeal: There's only one item to buy, no pieces to plug together. They're silent and power-efficient. They emerge from the box ready to work. But portable devices have limitations that can make them inconvenient if portability isn't your primary consideration. Their displays are too small. The need to run on batteries, and the cramped confines of a compact chassis put a tight limit on memory, storage, and performance. When you reposition the display, the keyboard and pointing device (real or virtual) move, too. Making computers portable also makes them expensive. As long as portables have these strikes against them, the desktop will live on.

[ Also on InfoWorld: "Thunderbolt MacBook Pro: The last notebook you'll ever need" | Subscribe to InfoWorld's Technology: Apple newsletter. ]

Apple thinks it's possible to have it both ways, to cross the convenience and efficiency of a portable with the performance and ergonomics of a desktop. Like other manufacturers, Apple has long toyed with this formula with varying degrees of success. The latest generation of iMac, Apple's all-in-one desktop computer, gets it completely right.

Occupying the equivalent desk space of an LCD monitor and requiring only one cable (power), iMac is a fast, capable desktop with a very un-Mac-like price tag. Apple's redesign equips all iMac models with second-generation Intel Core i5 quad-core desktop CPUs, faster RAM, gamer-grade AMD Radeon HD 6000M-series discrete graphics, Thunderbolt I/O, a Bluetooth keyboard and pointing device, a FaceTime HD camera, and marvelous speakers. A 21.5-inch (visible), LED-backlit HD display graces Apple's two value-priced models, while buyers of the 27-inch iMac are treated to a much higher-resolution display (2,560 by 1,440), a faster CPU, an upgraded GPU, room for up to 16GB of RAM, and a pair of Thunderbolt ports.

Traditionally, Apple has aimed iMac at consumers, steering commercial and professional buyers toward the much faster, more expandable Mac Pro. The iMac is still priced like a home computer, but for the first time, iMac's performance is as prominent as its design, in league with top-shelf single-processor desktops. If Apple's best stock configuration still isn't fast enough for you, you can upgrade to a Core i7 CPU and an AMD Radeon HD 6970M GPU with 2GB of GDDR5 video memory, enough to satisfy a power user.

The 27-inch iMac can actually accommodate two external dual-link DVI displays, each with a resolution of up to 2,560 by 1,600, creating a three-headed dream machine that still has room to connect to the next generation of ultrafast Thunderbolt peripherals. This isn't just new territory for the iMac, but for all desktop PCs outside the workstation class.

Thunderbolt iMac: Surprising performance The new iMac lineup features quad-core Intel second-generation Core i5 ("Sandy Bridge") desktop CPUs and AMD Radeon HD 6000M-series discrete GPUs across the board. The fact that all models share 6MB of L3 cache, 1,333MHz DDR3 RAM, and 7,200-rpm hard drives narrows the performance gap between iMac models enough that most buyers can simply shop for the display size that suits them.

iMac upgraders, as well as users of PCs with first-generation Core CPUs, will definitely feel the kick. Sandy Bridge's on-chip memory controller, roomy cache, and faster RAM contribute to Apple's claimed 1.7X performance boost over prior-generation iMacs, and that technology is common to all configurations. Even the bargain hunters get a ride on the bullet train.

Apple realizes that for some, fast isn't fast enough. A Core i7 CPU upgrade is available as an affordable configure-to-order option for both 21.5- and 27-inch models, bumping top clock speeds to 2.8GHz and 3.4GHz, respectively. Developers, creative pros, sci-tech workers, people who run Windows in virtualization, and others who routinely max out their multicore CPUs but lack the budget for a Mac Pro finally have a machine of their own. The iMac's Core i7 upgrades not only kick up the clock speed, but also expand L3 cache and add Hyper-Threading, likely adding a 20 to 30% speed bonus over Core i5. That's a meaty upgrade for $200.

The AMD Radeon HD 6000M-series GPUs that Apple chose for iMac are uncommonly powerful for mainstream desktops, rendering iMac's lack of internal expansion slots into a non-issue for most buyers. The 21.5-inch iMac incorporates either the AMD Radeon HD 6750M or 6770M with 512MB of dedicated GDDR5 video memory. The entry-level 27-inch iMac also has a Radeon HD 6770M with 512MB of VRAM, while the top-end 27-inch model (the model I reviewed) has a Radeon HD 6970M with 1GB of VRAM (upgradable to 2GB).

These GPUs don't transform iMac into a workstation (to keep a lid on cost, space, power, and heat, iMac uses mobile GPUs) but Apple has selected the market's best. These AMD mobile GPUs compare favorably with AMD Radeon HD 5000-series desktop graphics cards, which continue to be sought after by PC gamers. If you're currently an iMac user, Apple says you should expect as much as a threefold hike in graphics performance. If you're coming to iMac from Mac Mini, MacBook, or a mainstream PC that uses integrated graphics, iMac's GPU will take your breath away.

Mac OS X's frameworks and popular Mac apps deftly distribute the compute workload across CPU cores, threading engines (in the case of Core i7), and GPU shaders. Users will find that Apple's combination of leading-edge technologies from Intel and AMD add up to a smooth, exquisitely responsive driving experience. As nice as it is under Snow Leopard, it's almost sinful under OS X Lion.

Thunderbolt iMac: Benchmark results If you're considering pressing a notebook into desktop service, iMac's superior performance should factor into your decision. Benchmarks comparing a 3.1GHz 27-inch Core i5 iMac to a 2.2GHz Core i7 17-inch MacBook Pro show iMac to be the clear performance champ, and the thread-intensive SPECjbb2005 benchmark doesn't even highlight the benefits of iMac's desktop-speed hard drive. Although it's possible to configure high-end portables like MacBook Pro with a 7,200-rpm hard drive and an upgraded CPU, you'll spend a lot to construct a notebook that's in iMac's league.

I don't have a current Mac Pro for testing, but benchmarks run against an older eight-core Nehalem Mac Pro reveal iMac's generational advantage. The iMac scales remarkably well to SPECjbb2005's multithreaded workloads, even when pushed to run eight threads without the benefit of Hyper-Threading. The iMac has the headroom to handle a demanding mix of foreground and background tasks without bogging down the user interface. (See the table of SPECjbb2005 results.)

Notes: Thunderbolt iMac configured with 3.1GHz quad-core Core i5 CPU, 6MB L3 cache, 4GB of 1,333MHz DDR3 RAM; Thunderbolt MacBook Pro configured with 2.2GHz quad-core Core i7 CPU, 6MB L3 cache, 4GB of 1,333MHz DDR3 RAM; Core 2 Duo MacBook Pro configured with 2.8GHz dual-core Core 2 Duo CPU, 6MB L3 cache, 4GB of 1,067MHz DDR3 RAM; Nehalem Mac Pro configured with two 2.93GHz quad-core Intel Xeon CPUs, 8MB L3 cache, 12GB of 1,066MHz DDR3 RAM.

The iMac's CPU is capable of some impressive feats on its own, but it's Apple's ingenious pairing of top-shelf tech from rivals Intel and AMD that makes iMac tick. Mac OS X's OpenGL-based GUI suits any Mac, but it's clearly designed to run on a modern discrete GPU. AMD's Radeon HD 6000M-series GPUs are a Goldilocks fit for iMac: They have enough juice to smooth OS X's scrolling and transitional animations and deliver satisfying frame rates on 3D games, while avoiding the overkill in heat, power, noise, and cost that a Radeon HD 6000-series desktop GPU would bring to the design. Apple's decision to go with mobile GPUs may elicit a lukewarm response from hard-core gamers, but that's not iMac's niche. The iMac's architecture is optimized for Mac OS X, and vice versa.

Notes: Thunderbolt iMac configured with AMD Radeon HD 6970M discrete GPU; Thunderbolt MacBook Pro configured with AMD Radeon HD 6750M discrete GPU, Intel HD 3000 integrated GPU; Core 2 Duo MacBook Pro configured with Nvidia GeForce 9600M GT discrete GPU, Nvidia GeForce 9400M integrated GPU; Nehalem Mac Pro configured with AMD Radeon HD 4870 discrete GPU. Core 2 Duo MacBook Pro results are not directly comparable to Intel and AMD GPUs because a different shape is used, but do reflect relative performance.

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