The Late 2009 iMac comes in 21.5" and 27" sizes, and the displays have the same 16:9 aspect ratio as HDTV. The smaller iMac has the same 1920 x 1080 pixel size as high-def television, and the 27" beastie provides an incredible 2560 x 1440 pixels. Both sizes are LED backlit, and the 27" iMac also has Mini DisplayPort input, allowing another computer or video device (DVD or Blu-ray player) that supports DisplayPort to use the iMac's screen (it's not compatible with HDMI, DVI, or VGA). One feature new to Apple's desktop line is a built-in SD Card slot, which is on the right side below the SuperDrive.

Visually, the screen looks even bigger, as the glass now goes all the way to the edge of the computer - no more aluminum border around the display. And the back is now aluminum instead of black plastic.

Apple has simplified things by starting the iMac at 3.06 GHz and offering a 2.66 GHz quad-core i5 option for power users. Build-to-order options include a 3.33 GHz Core 2 Duo CPU and a 2.8 GHz quad-core i7 the i7 supports HyperThreading, which allows each core to appear to the OS as two cores; the i5 does not). 4 GB of RAM is now standard across the line, and maximum RAM doubles to 16 GB (vs. 8 GB for the previous model) using four 4 GB modules.

The base 21.5" model uses the same nVidia GeForce 9400 GPU found in most current Macs, and the step-up model has ATI Radeon HD 4670 graphics with 256 MB of dedicated memory. This GPU is also used in the base 27" model, and the top-end iMac has ATI Radeon HD 4850 graphics with 512 MB of video memory.

The Late 2009 iMacs have 4 USB 2.0 ports (one more than before), FireWire 800 (but not 400), gigabit ethernet, 802.11n WiFi, Bluetooth 2.1+EDR, an SD Card slot, and an 8x SuperDrive - as well as a slim keyboard with two USB 2.0 ports. This is the first Mac to ship with Apple's new Magic Mouse.

The entry-level iMac has 4 GB of RAM, a 500 GB hard drive, an 8x SuperDrive, nVidia GeForce 9400M graphics, and Apple's aluminum keyboard and Magic Mouse. 256 MB of system RAM is dedicated to video. All the other models have GPUs with dedicated video memory.

The more powerful iMacs include a 1 TB hard drive.

Intel-based Macs use a partitioning scheme known as GPT. Only Macintel models can boot from GPT hard drives. Both PowerPC and Intel Macs can boot from APM (Apple's old partitioning scheme) hard drives, which is the format you must use to create a universal boot drive in Leopard. PowerPC Macs running any version of the Mac OS prior to 10.4.2 cannot mount GPT volumes. PowerPC Macs won't let you install OS X to a USB drive or choose it as your startup volume, although there is a work around for that.

 iMac screen

The most obvious change in Apple's new all-in-one computer range is to the iMac screen. Both the 21.5- and 27-inch screens are made with high definition video in mind.

And the 27-inch model is, in a word, stunning.

Don't take my word for it. That's based on the cluster of techie-types and graphic designers who popped into my office last week to get a gander at the newest all-in-one Mac from Apple.

Part of it might have been the novelty: Apple unveiled these larger, widescreen iMacs on October 20 and sent one over for review purposes two days later.

It's the biggest change for the iMac since it went aluminium-and-black in late 2007.

Like on many HDTVs, the black border around the new iMac's screen reaches out to the very edge; the aluminium border that surrounded the screen in the previous iMac is gone.

Processor and memory

▪     21.5-inch and 27-inch models, one of the following:

◦                             3.06GHz Intel Core 2 Duo processor with 3MB shared L2 cache

◦                             3.33GHz Intel Core 2 Duo processor with 6MB shared L2 cache

▪     27-inch models only, one of the following:

◦                             2.66GHz quad-core Intel Core i5 processor with 8MB shared L3 cache; Turbo Boost dynamic performance up to 3.2GHz

◦                             2.8GHz quad-core Intel Core i7 processor with 8MB shared L3 cache; Turbo Boost dynamic performance up to 3.46GHz; Hyper Threading for up to eight virtual cores

Faster processors.

Quad-core power.

The available quad-core Intel Core i5 or Core i7 “Nehalem” processor in the 27-inch iMac puts four processing cores on one die, so data doesn’t have to travel far to get from core to core. This boosts application performance up to 2x over the previous-generation iMac.1 And unlike systems that connect memory to the processor through a separate controller, these quad-core processors connect memory directly to the processor, improving memory bandwidth up to 2.5x.2

Turbo Boost.

A quad-core iMac also benefits from Turbo Boost. If you’re using an application that doesn’t need every core, Turbo Boost shuts off the idle cores while simultaneously increasing the speed of the active ones.

Built for more cores.

Mac OS X Snow Leopard is designed to take advantage of this advanced processor architecture, so every Intel processor reaches its full potential on iMac.

Faster graphics.

Options for everyone.

iMac offers graphics options designed to make the most of every pixel. Whether you’re an amateur filmmaker or an avid gamer, iMac gives you faster, smoother, clearer graphics across the board.

Start with advanced graphics.

The 21.5-inch iMac offers great graphics performance with the integrated NVIDIA GeForce 9400M graphics processor or the ATI Radeon HD 4670. The 27-inch iMac comes with dedicated high-performance ATI graphics across the line.

Upgrade to top-of-the-line graphics.

The ATI Radeon HD 4670 graphics processor delivers up to 4x faster performance than the NVIDIA GeForce 9400M — ideal for 3D games and graphics-intensive applications. For the ultimate in graphics performance, choose a 27-inch iMac with the ATI Radeon HD 4850 graphics processor.