- 16:9 screens
They changed the aspect ratio of the screens to 16:9. Which is great if you’re working with 16:9 video. Otherwise, not too sure how it really helps/hinders the average user.
- 21.5 inch display is exactly 1920 x 1080
The previous model - the 20 incher - had a resolution of 1680 by 1050 pixels, not so good for watching/editing 1080 video.
- Core i5 and i7 quad-core processors
If you have the cash, you can get a quad-core processor. Unfortunately, not a whole lot of software makes full use of these…it will be interesting to see whether these chips make a significant improvement in compression times
- 21.5 model has 8-bit video
Previously, the lower-end iMac video was only 6-bit, so for those looking to use a low-end iMac for video or image editing, that’s good news.
- You can connect a second external display using the mini DisplayPort
- 27-inch can be used as an external monitor for MacBook using the same miniDisplayPort
It appears that you can't do this with the 21.5 model.
The bad news: No Blu-ray. Can’t say I’m really surprised, and yet I had been hopeful!