TUAW may have had the date wrong (we guessed October 9, 2009), but the new iMacs we were looking for finally showed up today. The 20" and 24" models are gone, replaced by 21.5" and 27" iMacs with a true 16 x 9 HD aspect ratio. It's also obvious that Apple intends for the new iMacs to end up on the desktops of a lot of designers, since the line now includes the first quad-core iMac ever.

The pricing for the iMac line starts at the same US$1199, but that's where the similarities stop. The displays are now backlit by LEDs, providing better energy efficiency. The 21.5" model has a screen resolution of 1920 x 1080 pixels, which is the equivalent of a 1080p HDTV. That screen size is actually 90% of the resolution of the old 24" iMac. Resolution on the 27" model is 2560 x 1440 pixels. Both of the new iMacs use the IPS display technology for excellent color fidelity and a very wide (178°) viewing angle.

For the first time, iMacs now have an SD card slot located below the optical drive slot on the right side of the computer. The systems will ship with Apple's new wireless keyboard and Magic Mouse, or you can get wired models as a configure-to-order option at no extra cost.

All of the new iMacs can be loaded with up to 16GB of RAM and up to 2 TB of storage. The new low-end model, at US$1199, is running a blazing-fast 3.06GHz Intel Core 2 Duo Processor and comes with 4 GB of RAM, a 500 GB hard drive, and an Nvidia GeForce 9400M video card. The US$1499 model of the 21.5" iMac bumps storage up to 1TB and upgrades video to a Radeon HD 4670 card. The US$1699 27" model has the same features as the US$1499 21.5", but of course has the 27" display.

At the high end of the line will be an iMac that won't be released until next month -- a $1999 27" that is powered by a 2.66GHz Intel Core i5 quad-core processor. That model also has a Radeon HD 4850 video card built in. If you wish, you can swap out the Core i5 chip for the even more powerful Core i7 processor.

The Core i5 is based on the Linfield processor, which is part of the same Nehalem family found in the existing Mac Pro line. The Core i5 features a turbo mode, which means that the chip can shift from a slower clock speed with four cores to a faster mode with two cores active. The turbo mode speed of the Core i5 processor is 3.2 GHz, while the turbo mode speed of the i7 is a whopping 3.46 GHz.

What's really incredible is a new feature for the iMacs 27" models that allows them to act as external monitors or HDTVs. You'll be able to attach DVD players, Blu-Ray players, gaming consoles, or even other computers, and display them on the bright, clear, iMac display. Update: The 27" will handle DisplayPort-based input, with adapters to be announced. The 21.5" model will not support video input, based on the spec page.

The last iMacs were released in March of 2009, with a 20" model powered by a 2.66 GHz Core 2 Duo available at US$1199, and 24" models with 2.66, 2.93, and 3.06 GHz processors at US$1499, US$1799, and US$2199.